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tet Britain fbr March. 1867, Dr. J. Bell rettlgrew. £&&-» the distinguished Curator of the Museum of the Jbojml College of Surgeous ef Edinburgh, announced the startling discovery that all wing*—whether thoae of the insect, bat, or bird—were twisted upon themselves etructurally, and that they twisted anduntwlsted daring their action—that in short they formed mobile AeJicea or screws. In June of the same year (1867), Dr. PWtigrew, following np his admirable researches, rend an elaborate memoir *'0n the Mechanism of Flight," before the Linnean Society of London,* in -,vh?.?h he conclusively proves, by a large number of «ilM*cMona and experiments, in which he greatly tveete, that not only is the wing a screw structurally and physiologically, but further that it is a reciprocat\i*2 etTcw. He shows, in fact, that the wing, during it* oscillations, describes a figure of 8 track, similar in aotue respects to that described by nn oar lu sculling. Thin Holds true, of the vibrating wing of the insect, bat. and bird, when the bodies of these animals are artificially fixed.

When, however, the creatures are liberated, and Hying at a high horizontal speed, the figure of 8. as he points out, is curiously enough converted Id to a trace track, from the wing beiug carried forward by the body, and from its consequently never being perxuitted to complete more than a single curve of the 8This is an entirely new view of the structure aud functions of the wing, and one fraught with tho deepest possible interest to the aeronautical world. It promises to solve everything. Dr. I'ettigrew s remarkable discovery has received an uulooked for confirmation within the last few months at the hands of Professor Msrey, of the College of France, Paris. ThiB gentlenzan, who has acquired great celebrity for bis improvements and dexterity in the use of the t>pbymograpb, has succeeded in causing the wing ol the insect and bird to register their own movement)*, and has established by an actual er/w imcn/MM cruris. the absolute correctness of Dr. Pettigrew'a views, trofessor Marey'a mode of registering displays much ingenuity, and is briefly is follows:—A cylinder revolving at a given speed is enveloped by a sheet of thin paper smeared with lampblack, and to this the tip of the rapidly-vibrating wing of the insect is applied in such a manner as to cause it to brush out its track on the blackened puper, which it readily <loeB. A similar result is obtained in the bird by fixing a registering apparatus to the wing, and causing the bird to fly in a chamber. In thiscaso the registering apparatus is connected with the cylinder by means of delicate wires, and the registering is effected by means of electricity. In both cases the figure of 8 sijd wave movements, originally described and figured by Dr. rettlgrew, are faithfully reproduced. It is difficult to forsee what next. The way of a-ving in the air has hitherto been regarded as a physiological puzzle of great magnitude; aud well It might be, since some insects (the common fly for example) vibrate their wings at the almost luconcetvublo speed of 300 strokes per second, that is, 18,000 times in a minute 1

SCIENCE FOR THE YOUNG.

Sin,—The uncourteou* tone of Mr. O'Connor's letter, p. 257, English Mechanic, imperatively for bids my inking any notice of its contents. Nothing would induce me to help on, even ever so little, that spirit of incivility between correspondents in the English Mechanic, which has done so much mischief in 'times ' now fortunatelv passed, to the real, the best interests of the journal. "Were this obstacle not in the way, it would bet easy to show Mr. O'Connor that a better acquaintance with "Science for the Young " would probably more than reconcile him to the divisions of the subject, and would certainly convince him that there was no reason for his letter.

E. Kern An, Clongowcs.

EMIGRATION.—TO "COTTON CLEBK" AND OTITKRS.

SiR.—Divert your attention for a moment from Canada and the other British colonies, and direct your thoughts also for a moment to other States, whether as regards Republics, or under other Governments—for example, South America. Not couutries which lie within tho Tropics, but in those broad, healthy climates which lie to the south of, say, Rio de Janeiro. From this point, lying southward, you come first to Santo Paulo, a district where lately, I believe, there lias been introduced a railway, through English capital, and gas works, and a region of great beauty aud fertility. Then you come to Parauaguaand cian Francisco; then to San Catherina and Porta la gre, all offering some splendid sites for emigrants, but some, of course, preferable to others. Then you come to the Tianda Oriental, the Kntre Riob (districtlying between the two rivers Uruguay and Parana), and lastly the unsettled but magnificent district of Paraguay, which gTowt* everything almost in the world. All these countries are either Republics, enjoying their own privileges, or are under the Brazilian Government. To thfi*- regions resort, every year, hundreds of Germans, thrifty and wise, who congregate together aud make their own peaceful settlements there, become farmers, and make their little fortunes. The oxuet FettlementBwhere these honest Germans live I do not precisely know; but they have this advantage, they have the country to themselves, and live in peace. I should say to this good and industrious "Cotton Clerk," place yourself at once in correspondence with any house you may know at Liverpool who trades with the Brazils—he will give you oil information; or, secondly, with any merchant trading with Buenos Ayrew or Monte Video; or, thirdly, if you know any German at Liverpool, Manchester, or London, he could tell you what hia countrymen are doing, Recollect, when yon go to a British settlement, you must pay for the fancied security. In tli« other countries on the Southern Main you may get quantities of land all but given to you—that is, in some of the above countries. You can ascertain for yourself what population there

* This memoir, which is Illustrated by nearlv 100 original figures, la published in txtenso In the 126th volume of the Transactions of the Society.

I rather think it is somewhat scant, and ihat everyone is hiB own workman; and, of course, iu a foreign country, where there are none but Germaus, it may be somewhat dull and dreary. But the Anglo-Saxon blood abounds cveiywhere, and facts you can get for yourself. I believe the safety and security of these lands are everything you can desire. The world is growing, through the influence of science nn'l education, somewhat' tired of war, and all peoples and nil languages are finding out that riches, well-being, and comfort are to be found In the pnrsuit of the peaceful arts of manufacture and agriculture, rather than in the barbarous pastime of war.

E. W. J.

COTTON SPINNING.

Sir,—Your correspondent, "B. W. R.," page 230, seems very much disposed to carry out the old adage —viz., to "pick a fellah up before he's down"—with respect to my letter on draughts. When will ye have wisdom, and hearken to the voice of reason, O ye cotton lords! Surely " B. W. R." must have penetrated very deep into tho mysteries of t'»e fibrous art to find out that a lap will bag if there is no draught between feed and lap rollers. Let me inform him, for bis edification, that we have at the present time about 140 carding engines at work, and if he cau find tho slightest draught in nny one of them, or the least sign of a slack lap, I dare forfeit the engine he finds it in. The same may be said with respect to the lap rollers of our combing machines. It may not be out of place here to remark that I flatter myself with having peuetrated so far in the art of cotton spinning to know that if the lap rollers move at the same surface speed as the feed rollers, it is impossible for the lap to bag. The following Is the draught (!) of our engines between lap and feed rollers :—Dinm. feed rollers, l$in.; lap rollers, 6in.; a 11 wheel on end of feed roller drives a 4B on end of lap roller. The result of the above, when well reckoned, will amount to about as much as " B.W. R.'s" penetration does. I want to know what use a draught would be if the lap is delivered ju«t as the feed rollers take it? How eau it bag? You just may aa well say that the break van at the rear end of a irain will get into the station before the engine that is pulling it. "B. W. R" also refers me to a letter of E. Slater, on the same page as my own, to convince me that there Is a draught. Certainly K. Slater may have n draught in his engines-, but if K. Slater has a failing (which it certainly is), it does not follow that it must be crammed into every person's noddle, whether they agree with It or not. By-the-byc, if all K. Slater's contributions are to be judged from his distribution of "Factory Lad's" draughts, and his "penny wise and pound foolish" Ideas about draw-boxeB; If we are to infer that these are "the truth, and nothing but the truth," then I must say that "B. W. R.'s" "penetration" has not been of much use to himself, or he would never have referred me to K. Slaterto be convinced of my error (?). "B.W. R." also loses his extraordinary "penetrating" powers when he states that the draw-box of a carding-engino is between the doffer and delivery rollers. He must mean between the doffer and coiler rollers, as the draw-box and the delivery rollers are the same thing —at least they are so called in this quarter of the globe. What I said then I aay now, that there is not any draught between doffer and delivery rollers—i. c, the draw-box.

The Harmonious Cotton Spinner. [Some of our cotton correspondents are somewhat inclined to "chaff"'each other. Thisisnodoubtamusfng to them, but they should remember it occupies valuable space which might he better appropriated. They and all others would oblige by telling us what they have to say in the fewest number of words, so that we may be enabled to give the largest amount of information for the largest number of readers.—Ed. E. M.J

SlB,—CONTRIVAWCn* FOfcTWTlNG THE STRENGTH

or Yarns, &C.—X shall be very much obliged if any of tho Cotton Spinning Company will give me some information about the above. The reasou of me troubling yon is this: I have an idea of making a simple machine by which you can tell the strength of yarns in lbs. and oz. without the aid of springs, or auy complicated mechanism at all about it. What I require is this—a brief explanation (accompanied by diagrams if fouud needful) of the most complete and simple contrivances now in use, that will give the strength of yarns from SO* single, down to i'O*1 12 fold heald yarn. If I find that there are more simple and correct ones than mine (which I am not so self confident aB to doubt at all), then of course I shall not go on with mine; but if I see that mine will have any advantage over the others in use, then 1 shall get one finished, and trouble you to give a description of it with a sketch, so that 1 can submit it to the penetration of your uow numerous body of cotton spinning subscribers. I shall be glad when auybody replies to the above, if they will give the nameB of the makers, and where I can obtain one. I beg to return my thanks to Joseph B. Orossley (p. 254) for his recipe for size for cop bottoms, which I rind to act very well, especially with a bit of fish glue added to it. He Is right in saving that the difference in the make of frames will make tho results of experiments very considerably, but I cannot understand (except from that cause) how he can run his frames faster with the bobbins leading than with the flyers leading. Of course there Is not much difference when the bobbins are full, and they are leading, and you are making about a 12 hank roving, but when the frames are just starting a fresh set, and the bobbins are empty, and you are making soy $ hank stubbing, then is the time the poor tubes "get it hot." I have not very much spare time at present (aud probably you have not much spare room) or I would go Into this much-neglected subject more fully. Early information on the yarn testing subject will greatly oblige.

Tins Harmonious Cotton Spinn£r.

Sir.—Draught Of Drawing Frame—On page 136 " Factory Lad " asks: "Suppose a drawing frame to have 1 lines of rollers, with a total draught of 7,

what draught ought there to be between the 1st and 2nd, 2nd and 3rd, and 3rd and 4th rollers?"

On page lft3 E. Slater, Burnley, replies thus: ** Let 'Factory Lad,' page 130, divide his 7 by 3, and make the draughts of each liuo of rollers hi the drawing boxes equal, as 2| + 2$ + 2£ = 7, or 2\ + 2\ + 2\ - 7.

On page 231 Mr. Slater corrects himself lu the following words: "My meaning was (from front to back), between front and 2nd roller. 2'5; between 2nd and 3rd, 100; betweon 3rd and 4th, 1 C7. Or, reversing their order, 167 x 109 x 2 5 = T'O.'iWS. or something as near this order as he should find convenient. I was once rarely puzzled by a similar answer, given to me by a very intclligentold man: however, I learnt something from It, and if you think yon will do the name."

Now. I submit that if Mr. Slater will think, he must think that it would tend more to the improvement of our contributors if he would kindly write what ho means at once; for 1 dare be bound he is the only person who reads his two replies who will find the least possible resemblance between them. Ho says hia object in writing is to set us thinking. It certainly will; but it leads me to think he ought to be a little more consistent, " especially when, as In this case, the subject is a very important one."

Mutual Improvement,

Sin.—Edward Habcrgham, p. 204, says he Is wishful to understand the backing off motion, and the operation of the cam shaft. The term "backing off" is applied to the reversed motion of mule spiudlcs at the finish of a " spinning stretch," by which the coil of yarn that the spinning action has thrown upon the bare portion of them is unwound down to the point of the cop, so that the action of winding may commence on the body of the cop. Now, observe, this backing off action must tako place at tho same time, and correspond in its speed to the downward motion of the fuller; for if the spindles buck off quicker than the taller goes down, the yarn will be thrown off iuto "snarles;" or, if slower, it will be over&trctched,and the bottom coils pushed down in a slovunly manner to the cop shoulder. And, moreover, as the cop is continually increasing in length, the backing off must be diminished in the same proportion. From this, then, it is clear that the two distinct operations, the locking of tho faller and the backing off of the yarn, must by some means be made to depend upon each other. This has been ingeniously accomplished by many different arrangements of levers and cams, &c.; so I will now try to explain their action and principle. See the Bketch, which, I may observe, is not intended to be a correct representation of auy working mule, but to illustrate the actions, and help to convey some Idea of the cam shaft and backing off mntiou. 1 is the backing off disc or cup, to which a retarded motion is given from the pulley 3 by the wheels i. o, 0, 7, and 8, and this iu an opposite direction to that of the pulley 2 and rim. The pulley 3 is loose upon the rim shaft, and connected to the wheel 4 by a long boss. 10 is the ordinary loose pulley. Fast u^ou tho rim shaft is the friction cone 11. The surface of this corresponds to the inside of the cup 1. Let us now suppose that a stretch has been spuu, and that there is some kind of a bracket fixed to the carriage, which comes in contact with the long lever, and causes it to fall a certain distance at the front end. This action of the lever will cause a corresponding rise of the connecting rod a, which in its turn will lift up an escape lever, b, that has been holding against one of the pallets, c, on the end of tho cam shaft, A. As soon as tuiB takes place, the cam shaft having power given to it either by a friction bowl, a strap, or other means, turns round until another of the pallets comes in contact with the escape lever. But suppose this first movement of it ha*, by means of cams that are attached to it, caused the strap to be thrown on to the pulley 3, and the disc 1 to be pressed against the cone 11 by the lever />, it is evident tbat the disc will not only act as a brake to the rim shaft and spiudles, but when it has stopped their motion in one direction it will then turn them in its own, or reverse their first direction, aud that this action will go on as long us the cam E> presses the disc against the cone, or eo long as the cam shaft keeps this condition. However, as soon as the rim begins to move In a backward direction, tte catch x conies in contact with the teeth of the ratchet wheel y, which is fixed upon the same shaft as the pulley 12, or spindle shaft. Tho ratchet then cau.seH the ring z to turn round along with the shaft and spindles; and as the chain 13 is attached to this ring, the motion is corumnnicated by this means to the "faller sector ** 14, which is pulled down at a speed corresponding to that at which the yarn is beiug unwound, until the latch 15 falls at the end of tho sccror, and locks the faller. The falling of the latch 15 allows the lever 10 to fall also, and this, through tho rod 17, allows the long lever to fall another distance, which in its turn again liberates the cam shaft from the contact of escape lever and pallet. The cam shaft now turus a distance further, and throws back tho disc to its loose position upon rim shaft, and, at the same time, by other cams and levers, throws tho putting up wheels luto gear, and the carriage runs up until the long lever Is pressed down again at the back end, aud the cam a^.iin is allowed to complete its revolution, throwing spindles, rollers, aud carriage into gear all at once for auother stretch.

1 may observe that the first motion of the cam shaft at the finish of the out stretch of the carriage is often made to throw the rollers and carriage out of gear, whilst the strap is still allowed to drive ou the rim pulley for the purpose of putting extra twist iu tho yarn. "When this is the case, the cam shaft will be held stationary by some such arrangement as a worm and bell wheel would give. It is well to observeatso, that the less the cops are, the higher is tho builder, which causes the latch 15 to be thrown farther back on the surface of the sector U; and the farther back this is thrown, the longer will the spindles back off before the cam shalt is liberated by the falling of the latch. The arrangement of wheels, cams, levers, &c, that have beee contrived to produce these various conditions and motions to such a degree of perfection as we now find them, has required a great amount of ingenuity; and to understand their working thoroughly will be well worth the trouble Edward Babergbani may devote to the purpose. In fact, the self-acting mule is a wonder in itself, and a credit to English ingenuity. I liave perhaps said enough now to put him on tbe proper track when be watches the mule in operation; if not, I shall be glad to render further help. 1 beg to thank him for his kind words; :iud if I have been of Bervice to him, 1 am by that fact repaid for my trouble.

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I see in this week's Mechanic that my answer to "Factory Lad " has brought a "curt-load of bricks'* on the top of me, " I beg to tinder my grate thankfulness for lhat same intirely," However, I had no idea whatever that he would receive so many answers in return ; but I have an idea that some mischief might be done by him or others acting from Insufficient Information, and wab quite willing and prepared to give both further explanation and "reasons" fur what I have said. Look at the circumstance of C. Haltnshaw, of Corners*], having begun to alter some jack-frames —roving or elubbing frames—before he had looked properly through the job, and this, too, frum an ii/?a that he had gathered from a communication by "B. It. W.," which I am positive that gentleman never intended to couvey; and I think your conclusions will be like my own, that no one ought to act upon the information contained in a short, isolated answer from anyone. An Important machine like a drawing box, one single bad roller in which will spoil the work of 1000 mule or throstle spindles, should not be altered without a thorough knowledge of the *' why *' and " wherefore." It is said of Arkwright, the inventor of the frame, that when anything was wrong with his yarns he told his men to see to the drawing boxes. "The fault," he would say, "is sure to be there." I do not say so myself; but thla showed thai he fully understood the importance of them. As I stated in my last, an answer similar to the one I gave him caused me to think, and marfr me learn. J asked an old manager how he would distribute a total draught of six in four lines of drawing rollers. His answer was, " Have a last draught of two, and add the other four by the first and the intermediate ones." However, I will return to these same drawing boxes again, and I think 1 shall he able to lift a few of the bricks on to some other of the answers that have so far been given to " Fuctory Lad." But as my object would not be served by " banging them about," I will try not to get in a temper, and " duft" both myself and those who differ from me, like some of the millers have done.

I Bhould like to call the attention of ".Mutual Improvement" to thene two extracts from his letters: —" I quite agree with ' B. \V. R.' the rule I quoted does notgive the draught sufficiently accurate. The draught should be the difference between the surface speeds of the first or feed rollersand the last or delivery rollers." "Harmonious Cotton Spinner" seems to understand his business. He in perfectly right: "Let the rollers take up properly, and there will uot be any material draught between dollar and rollers." Did he not ask if the rule quoted was " strictly correct .'" And now. when he has got answers to what was, as 1 at once supposed, an ambiguous question, he makes it appear that both sides are perfectly right, though one says ** yes " and the other " no." I have uo doubt whatever but that "B. W. R." and "H. C. S."are both of one mind about the subject of a draught between lap roller and feed rollers—Me l*us that can be >nade to do ami the better, just enough to keep the sheet of cotton straight. Is all-sufficient. Bow would "Mutual Improvement" manage to get the gossamer-like web from the deffer to the calenders without some slight, gaining motion of the latter, when even a breath of wind will stretch it out and make it slack? I will give my reasons for condemning draw-boxes shortly, but I may here say that thougn "some of our most successful spinner* work them," it doeB not at all follow that their success is due to the draw-boxes; possibly it may be in Bplte of them. With respect to the question raised about bobbins or flies leading. I am in favour of the bobbins leading, because It make» a more equally pressed bobbin with less waste. And, bear in mind, the waste that flies off tbe broken end, when the fly leads. Is not only waste, but very mischievous waste, as It gets entangled with the other ends that are running upon tbe bobbins, and causes thick, slovenly places in the yarn, that aie a perfect—if I may use the word—eyesore when the printed cloth Is examined. "H. C. S." says, page 204, " Let any one try to start a frame with the bobbins leading and the spindles running 900 per minute." My answer is, that ours run. with no inconvenience, at about 1280, or between that and 130' per minute, making about n six hanks roving. But, by the way, what Mill "B. C. S." think when I tell him, as I do now, that be must by some means or other put his cart before his herse if he intends it to go?

K. Slaixs, Burnley.

HEATING GKKKN HOUSES.

Sir,—There have been many ideas and plans discussed in your columns for the heating ol greenhouses, but not one, *»s far us I see, suitable for a window conservatory. Now, I, in common with mauy others, have erected one of these miniature affairs against the window ot my sitting-room, aud there, during the whole of last summer and autumn, even up to Christmas Pay, my geraniums and fuschiai grew and blossomed in abundance; but the first sharp frost converted my little fairv scene into one of woe-be^one desolation. Then, and not, till then, did I set about discovering some cheap and simple means for excluding that merciless fellow. Jack Frost; and having studied the pa^es of the English Meciiamc for some time past without getting any suitable hints, I have in veined a simple apparatus, which I think would do what f require, though 1 should like the opinion of your practical readers as to the feasibility of the plan before going to the expense and trouble ol making. 1 therefore beg to enclose you a rough sketch, and should be glad if you think it of sufficient general interest to engrave. The apparatus 1 will describe thus:—A rather lirge glazed earthenware pipe (.1), with a collar, is suspended from tbe floor of the conservatory C, iu which a hole is cut the same size as the inside measure of collar of pipe. Within this pipe is a second D. of about half the length, and a little smaller, made of Iron, say sheet iron, into the top of which is fi'ted a ltd like a saucepan lid M. on which rests a shallow iron pan containing sand A. upon which to stand pots for striking cuttings. The heat is got from a gas coll H, above which, resting on three stud? or pins fixed in the sides, is an iron ring with iron or copper gauze stretched over it, so as to fir the iron pipe or drum, and above tliis still is another iron ring K, with copper wire stretched across at inter*

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vals, so as to form a kind of net work. Upon this net, work are placed very small pieces of pumice stone K to the depth of about -in., or less. The gas then ascends through the gauze and pumice stone, aud is lit on the surface of the latter, which 1 believe would get red hot, and so hold the heat. A pipe B Is inserted In the iron drum, near to the top, to carry olf the fumes; and this pipe cau be carried round the greenhouse, Bo that the heat it contained could be used. The end of it must, of course, be carried outside the house. V Is the gas supply pipe for supporting the iron drum within the glazed pipe. Pieces of Iron could be rivetted on to the sides, and bent out so as to rest on the collar of the pipe, or the bottom of the pipe could be stopped up all but a little hole for draught, aud Btones or bricks placed inside, upon which the drum could stand. To light the gas, tbe tray and saucepan li« would have to be lifted off, a match put to the pumice stone, and the lid and tray replaced, or, whtn not striking cuttings, the tray could be put away altogether. I think very little gas would suffice to keep up sufficient heat, aud any smith or Unman could make the apparatus. I should like to know if the pumice stone would last long, or if there is anything better that could be substituted. Would asbestos be better?

HOKTUS.

A CLIP FOB HOLDING PAPERS. Sir,—I beg to send a drawing of a simple contrivance for holding blotting paper, or letters,

flaps, which have little points to insure n Ann hold, and a pin passed through the interlocking loops it their edges. If necessary, the end of the pin may tv shaped as a hook or ring, so that the clip, aud 11k papers held by it, may be hung up on a nail. The els? is so simple and so clearly shown in the engravuv that it requires no further description.

J. C

SPECULUM GRINDING. Sib,—For more than two years I have read with deep Interest our Mechanic, especially those letters on speculum grinding, polishing, figuring. Ac, and telescope construction in general. I now wish to add my mite to thegteat mass of information already given- Soon after " Arcturus*' gave instructions for grinding aud polishing a V2\u. mirror, I set to work a 7 ■'> lain, mirror, using an iron tool proportionately larger, and succeeded M far as to be able to get some pleasing views of the moon, likewise of. Jupiter ami his moons, with very slight traces of Wb belts; but with high powers my mirror was useless. Yet, uot liking the idea of being beaten, I did as 1 waa once taught by a music msster-viz.,"Try,try, try again." but still with no better success. I now abandoned this, process to try that of the Iter. Mr. Cooper Key. I accordingly reduced my iron tool to the size of my mirror, aud again set to work, when in Bteps Mr. Parkiss with his valuable instructions. These, combined with my past practical experience, helped me neatly. I have now ground and polished two mirrors, the first being but a poor specimen. Nevertheless, I silvered it and kept it for use, intending to go over k again when I had made a better one, which I believe I have now accomplished. I have not as yet tried it on tbe heavenly bodies, but have tried it on a piece of paper cut from the English Mechanic, containing an engraving of Cameron's steam punch and IU or K* lines of letter press, the smallest but one to be found therein This piece of paper is pasted to a tree UD yards distant. I have examined it with three different powers—viz., 100. 213, and 309. With the two first powers 1 can read distinctly the contents of iho paper and see the finest lines in the engraving; hut the last-named power is almost too high for want of light, as my mirror is yet unsilvcred; hut still, wlia sustained attention I can read it. In the case of the two first powers the lines in the engraving, with the large and small letters, are well defined, clear aud black, without any appearance of mist. I Invite the opinion of Mr. Purkiss aud our kind "F.RA.8.." as iny own experience is rather limited in these matter*. The eyepieces 1 used were only double convex lenses. aud no sun shining during the test.

Optical Bricklayer.

INDUCTION COIL INSULATION.

Sir,—Perhaps it might be interesting to some of our amateur electricians of the Mechanic to inform them of a mode of Insulation that I have tried, and which I think Is very successfnl. 1 think it is equally as good as gutta percha tissue, or Bhellac varuish, and very much cheaper. It is made in the following way— Viz., 2oz. resin, add $oz. raw linseed oil, and melt them in au old earthenware pot. near the fire, frequently stirring. When the resin is thoroughly dissolved, add 2oz. spirits of turpentine, it is then ready (while warm), for painting on newspaper, or other thin

Caper, with a camel-hair brush (or an ordinary paiut rush will do); when gone over (evenly) hang up to dry, which will take three or four days, in a cool place. When dry, cut Into narrow shreds the full width of the reel or bobbin inside. When I got the primary on, I filled each lateral layer with warm paraffin wax, so an to make an even surface. I then wrapped two thicknesses of the above paper ou, before beginning the secondary, which I built in tho following manner—viz., one layer of wire, rubbed with paraffin, then one thickness of the above paper, and so throughout the whole of the secondary.

D. F. Abhton.

SIMULTANEOUS EQUATIONS.

Sin,—I venture to hope I did not in tbe lea-1 wayhurt the feelings of my dear brother correspoudeut **C H. W. B." I bee to assure him thta was not at ■II my intention. Ol course, if Mr. Todhuuter give* these problems »nly aa exercise of the 2nd decree two t...In limn are sufficient. I believe that several author

?\ve the problems of the form x*" + px" + o = "■ n which the expoaeut of x in the first term is double of that Hi the second, and which can be solved by the *nd decree only to exorcise the pupils in algebraical practice. The valuable German treatise of E. Heis, (tint lyine before me, gives also a collection of them. Several problems of Mr. E. H. have been translated rnto English in the " ICOO Algebraical Teste," by Mr. T. H. Cayzer, London, 1861.

Bernardix.

REPLIES TO QUERIES.

HOLTZAPFFEL'S CUTTER BAR.—"C. W. A" asks for n nkdch of above, which 1 send copied from Vol.11. I don't quite agree with him about toft wood turning, at

EXTRACTS FROM CORRESPONDENCE.

AN ENGLISH MECHANICS SOCIETY FOR LONDON.—"G. O. B." writes:—" How is It that the metropolis is behind the provinces la the establishment of a mechanical association? Certainly there mast be numbers ol suitable men In and about London to lorm aflrst-claas society. Will a few favourablydisposed gentlemeu, with scientific and mochaulcal inclination and ability, send me their names and ml■dresses, with a view to holding a preliminary meeting? I should like to invite, :by their noma de plume, many of your able correspondent**, but it would be Invidious to do so; besides, unless the <lesire I* mutual ami spontaneous, the affair would be weak and insipid. I shall be happy to receive any response to this, either through our Mechanic or by post, addressed to G. G. B,, Klpon Lodge, Grove Park, Camber well."

VELOCIPEDES.—"Isle of Ely"says:—"I think my brother readers are rather hard on Mr. H. W. Keveley. The 30 miles per hour I cannot believe in. but attfl he has bit the right nail on the head, for a alow motion of the legs, and a quick motion of the wheels, are just the things required in a veloce. We have another tempting bait in 'Leo's' veloce, now this has been tried, and he states it will run at the rate of 15 miles perhour. If this be true (but I am inclined to doubt it), no crank velocipede can come up to it. He would greatly oblige us by giving a clearer description, if as any ether reader seen this jnachine? I have tried many different kinds of velocipedes, but never one of a swinging motion. It seems tome you cannot get tho power with them you can with others. What Is the width between the swinging bars of the back wheel bicycle? I cannot see how the steering wheel la kept from coming against them in turning a corner."

CLAIRVOYA.NCE—"Solicitor" says :—"Perhaps the following case may interest our friends ' Sigma' »nd 'Harmonious Blacksmith.' Some years ago a relative of mine arrived at home unexpectedly one evening from Buenos Ay res, the door was opened to him by oue of his brothers, and almost one of the first questions asked by the absentee was, 'Is your wife living-?' The reply was in the negative, calliBg forth the exclamation, 'Ah, I feared as much, I saw

heron board our ship on the evening of (1 forget

the exact date), f may say the date was the day of the lady's denth.'"

DISTANCE OF TH E SUN. Ac.—'* Hugo " writes :-'Allow me to tell 'Veritas' that angles are not proportlnaal to their tangents, as he seems to think; and.therefore, it is not true that'the mean distance of the sun is to the mean distance of Venus from tbe earth as the mean horizontal parallax of Venus la to the mean horizontal para'lux of the sun.'"

"AB INITIO" CORKECTED.-'J.Dyer" says:— •« I am at a loss to understand ' Ab Initio.' He soys, 'Philadelphia, for instance, has its time 5 hours earlier than London, it being only 7 am. there when it Is noon here.' If tbe rotation ot the earth was from east to west this would be the case, but as It turns In the opposite dlrvction, looking south, any place west of London, as Philadelphia, must have Its time later, or after Loudon time. How noon can be after 7 in the morning < f the same day, or how the time of *a place with the sun on its meridian can be later than another 75 Uee,, or 6 hours to the west of it, J know not. If the time of Philadelphia in 5 hours < arJier than London time, then the time at London is 2 hours earlier than the time at St. Petersburg, and so. When Wednesday of the ssmn week la, in point of time, earlier than Tuesday, then will this he, but uot before."

[graphic]

TOTATO KEFORM — In allttlotract called "Potato Culture," Mr. F. W. Wllkins points out to us a method of generally increasing our potato yield, which U worthy of the most careful trial -, for, it his experiment* are correct, he has put us in tho way of quadrupling the -rop of this most useful vegetable. At present, potatoes are planted in rows, about 2ft. apart, and 10 or 12ta. from each other, the average produce being 2W bushels to the acre, or 6 tons, worth (say, at 3a, per bushel) about £30 per acre. By the new method, large whole potatoes are selected, and the eyes, all but one or two, scooped out They are then planted 4in. deep, in rows 4ft.. or, if very large, 5ft. apart. The result is, that each plant produces from baft a bushel to one bushel, the potatoes thomselves weighing 21bs., 3Ib»„ 4lbs,, oroveu 61bs. The yield of the acre therefore Is 13BO bushels, instead of 240, and the acre will bring In to the fortunate owner £204 instead of £3(». The rahona e of the proceedings seems to be, that we dwarf aud stunt our potatoes by overcrowding, like wo do our children in towns, and that the proper mode of treatment is to give to each po'ato aulhcfrnt room to expand, regarding It. in fact, like a young tree. The plants, iudeed, grow to such a size that they are obliged to be supported by pea-sticks, to which they must be tied 1-kehopa to poles. We moat strongly recommend a trial of this new form of potato culture to our gardening readers.

least I never could drive too fast for a good remit. Fig. 1 is a front view; Fig. S perspective view; Fig. 3 shows elevation of a cutter for threads ot high pitch ground nway to clesr under the cutting edge. Also plaa view of a thin and a thick cutter for S different pitches. This tool is more expensive, sad not so good as mine.—J. K. P.

[2538.]-INCRUSTATION IN POROUS CELLS.—The querist asks a means for preventing the incrustation of the cells of his hnttery; the following arrangement may, I believe, suit him. I imagined this battery some weeks ago, and one is working now since 18 days with the greatest regularity, serving several clocks, and having nearly no incrustation at all. I put in the jar ordinary water and a zinc plate, and in the cell a mixture of water and l-25th part of sulphuric acid and a small ptste of copper; and am, Hi far as yet, quite satisfied with the results.—D. N. Omiar, Belgium.

[2558.]—Sl'X DIAL —I w«s much struck hy the very simple method described by your correspondent "Auon," in your impression of May G, 1870, of obtaining a true meridian fine—viz.. hy the " ordnance maps " and " railway time," and began to doubt the old-fashioned method, which I have always adopted when I desired to ascertain mv meridian, as determined by equal altitudts on a horizontal plane by a perpendicular style in the eeutre of concentric circles, which requires neither ordnance maps, railway time, nor settiug a watch hy a dial, involving equation of time, &c, but only a clear, sunshiny day, or intervals of sunshine, at periods of equal altitudes. This method is so simple, so often quoted, and is found in so large a number of wnrl-s r*»t 1 «hon!'l imagine that every reader of the English Mechanic >..,«.. be acquainted with it. When once a true meridian line is obtained, and permanently marked, it is very useful tor a variety of purposes, setting a sun dial included. I have one in my garden consisting of » stretched wire about 10ft. long, which is nttHched to a tall stake truly upright, and which passes to the centre of the south pier of my telescope. When the shadow of the west edge of the stake coincides with the shadow of the wire, both being received upon a stone povemenf, the sun trHiisits the meridian. 1 find this exceedingly useful for obtaining apparent time at noon.—W. R. Birt, Cynthia Villa Observatory, Wnlthamstow.

[S675.]-NAVAL ARCHITECTURE—In answer to some correspondent who asked a question on this subject about two weeks ago, 1 am able to state that there are not, and never have been, any evening classes at South Kensington, for the purpose of teaching the above. There is in the South Kensington Museum the " Royal School of Naval Architecture und Marine Engineering," in which both these subjects (are taught. Very full information concerning it may be obtained'by writing to the Secretary, Science and Art Department, South Kensingtou Museum.—K. W. G.

[3707.]—TWISTING POWER OK METAL.—Molesworth's "Pocket Book" gives the following table of the "relative powers of metals to resist torsion ":—Wrought iron, 1*00; cast do., '90; cast steel, 1 93 —Stkkrsman.

[3746.}—TESTING BOILER-Having opened the flues so that a thorough inspection of the outside of the boiler may be easily made, run the boiler full of water, and get an ordinary boiler maker's furce-puiny, which may geuerally be obtained on hire from any bo'ler maker or dealer in machinery. Having connected the pump to the boiler by means of the feed-pipe or otherwise, close alt other orifices except the one leading to the pressure gauge. When the finger (if a Bourdon) or mercury points to the required pressure, let your man make a careful examination of the whole boiler. It were best that a boiler-maker or engineer should perform this duty, as he would be able to remedy any defect; and if there be no sign of leakage you might work safely under steam to one-fourth the indicated cold pressure. Thus, supposing the boiler so found to be in good condition, and you prove it to 1201b., you might work up to 301b. under steam, but do not trust to your own idea ot its state, as there might be some defect which would escape your attention, but catch the eye of an experienced man at once.—T. S. Conisbee.

[37fi5.]-TURBlNE WHEEL.—" A. B," will hy this reply see the rationale] of my request to be supplied with some data. A 1-horse power turbine with a 20ft. head of water would require 35 cubic feet per minute. His (in. pipe would supply onlv 0304 cubic feet, the loss in friction with such a small feed being enormous and quite useless fur any practical purpose. There is no special line ol demarcation between that which is a high or low pressure turbine. 1 should call any turbine with a head of water of from 7 to Hft. low pressure. The writer knows of a very powerful tnrhiue working with only 9iu. of head, and he has erected several up to Hit., and one with a head of 2C0rt.p with a supply of only 200 cubic feet per minute, which gave an indicated power of over 60 u. p.—Sknkx.

[3780.]- AREA OF SAFETY VALVES AND PISTONS'I note a remark by "Mutual Improvement," p. 260, as to corrugated pistons. Perhaps he is not aware that not only has that very thing been done, but it is patented. I once had a hot argument with a somewhat eminent engineer who believed in the notion, while 1 contended, of course, that though the surface was increased, and with it the pressure, still, us the increased pressure was not in the direction of the motion, there was no gain, and the effective work is only due

to the plane -*rea or section of the moving surface—f <*., the piston or valve. As to the latter, the figure given by "Q. Q. R." is the best, as giving the least resistance to the escape of the steam.—Sh.ma.

[3835.]-CLEANING COINS.—The best way to clean silver coins is to Immerse them in spirits of ammonia, which will thoroughly clean them without injuring them. For copper coins a \ceak solution of nitric arid—J. H. D.

:3839]-COLOURING TRACING PAPER.—A little oxgall mixed with the pigments will make them flow readily on the cloth or paper, and "Tracing" should paint on the tinder side of his drawings so as to show through the cloth.— Solicitor.

[3*43.]— FLY ROD.-In reply to "Regular Subscriber,' the joints of my rods are all tongue and socket joints, being in my opinion the best. The ferrate is fitted upon the joint far } of its length, let in the thickness of the brass. The socket is bored with a slight taper first with a spoon hit, and finished with a taper round file. The tongue is made to fit tight J of its length, allowing | for slackness, occasioned by wear. The ferrule should not be made fast until the boring nud fitting are satisfsctorilydone, as it has to be taken off now and then to see if the hole is straight and smooth; always keep it on, however, when boring or fitting the tongue in, else the wood will split. Next, paint the joint with whitelead, drive the ferrule well home, and fasten with two brass pins at right angles to each other, one t from the base of brass, and one an inch from the same. The ash I get on my own property—it is better to be cut from a tree, aud not more than 9* diameter. The outside is the best, and it must be reedy, and free from Jgnsrls or cross grains, and very well seasoned before using. The hickory, or lancewood, I pick up where I can, generally getting what I want in a coach factory or scantling yard. I stain my rods with logwood and alum

which gives n dark plum colour; never stain with an acid, as it generally destroys the wood, burning all the juices of the timber rignt out, and rendering it what is technically called "frush." The lapping is done with strong saddlers'twist silk, well waxed, and the whole varnished with coach makers' varnish. The butt end of rod may have either a Bpike attached, or finished off with a piece of horn or brass ferrule. Auy further information will be given cheerfully, free, gratis, for, nothing. I send a sketch of joint—Vivis Spkhanui'm.

[3851] -TO CLEAN SADDLES.—Wash with yellow soap, and dress with the smallest possible quantity of ueatsfbot oil. When the oil is dried in, use beeswax dissolved in turpentine, apply witli a brush, and polish with a soft cloth.—A Nkw Subscriber.

[38d2.1- BRASS INSTRUMENTS —The bends in brass musical instruments are made by filling the straight tube with lead or pitch, and after the correct curve is obtained the substance is melted out.—Solicitor.

[3856.]—TRICYCLE.—" W. B." will find 4ft. 6in. wheels worse than useless for any kind of velocipede whatever. Velocipede wheels should never exceed 3ft for ordinary roads. Never forget smalt wheels and long cranks for ease. The following, I think, would be the best tricycle for two on a long journey; although bad to turn round, it will easily turn out of the way. The front wheel just the same as a bicycle front wheel; the two hind wheels, of course, with a two-erauk axle; all the cranks one size —say Sin.; all the cranks connected by two ash treadles. Both men would step alike; the treadles would have long eyes on the front cranks, to allow for a little turning out of the way. The foot is not required to press fiat on the treadles, hut tbe same as if in a stirrup, so that the foot is always in a straight and easy position. The hind man would require a hand hold on each side, so that he could press well with his feet. Hand levers would not be required. A better velocipede for two on a long journey cannot be made; two hind wheels 2flin. apart—not more.— Andrew Johnson.

[38G4.]-EXTRACT OF DANDELION—"Sable " sends a "Poor Blacksmith " what he asks for from the Pharmacopoeia, it is the article of commerce :—Take of fresh dandelion root (bruised) 2ilb., boiling distilled water 2 galls.; macerate for 24 hours, then boil down to 1 gal..strain white hot, and evaporate to a proper consistence.—Sable.

[3868 ]—WATERPROOFING CLOTH.—" A. S. A." asks for a recipe for waterproofing cloth. Though my answer is probably not quite what he wants, yet it may help others. 1 tried it as an experiment, and found it to be a waterproof, though that was not my design in doing it. I wanted to fasten two thicknesses of black calico together for a photographic tent, so I laid a sheet of thin gutta percha, procurable at any chemist's, between the two pieces of calico, and theu ironed it with a flat-iron as hot as I dare use. The cohesion was perfect; it was a waterproof and light-proof too, and very easily made.— Countrt Parson.

[386<*.]-WATERPRO0FING CLOTH.—lib. of sugar of lead, lib. of alum, pound separately, and mix in a basin, and then pour 2qts. of boiling water on the mixture; let it stand 6 hours, and then bottle off for use. Apply to the cloth with a sponge or soft brush on a table till well saturated, and then iron it over and hang up to dry.—(From the Field.)—A New Subscriber.

63884.]—STEAM AND WATER.—The two motive powers of steam and water can be applied to the same shah. As water is the cheapest mode of driving, of course it is used to its fullest extent first, and what is wanted to be gained in speed or power is added by the engine, a competent engineer being always able to tell whether the wheel is driving the engine, or vice versa. In all cases where a wheel and engine are in connection, they should both be started at one time, the wheel driving and the engine gradually brought up to the required speed hy the engineer at the valve.—Vivis Sperandum.*

[3883]—MANUFACTURE OF OXYGEN.—See G. E. Davis's letter.

[3386.]—WA1ER ANALYSIS —See G. E. Davis's letter.

[389*.] —IRISH RING MONEY. — I beg to refer "Daukoien" to a papor read before the Royal Academy by Sir William Betham, M.R.I A., Ulster, King of Arms, printed at Dublin, in 1836. I would give the quotations, but they an; too long. He attributes the date of them to be several centuries before the Christian Era, and used by the Phojuicians in barter, to whom he assigns tbe invention. He says , u Cresar * ills us that the Gsuls use for money gold and iran rings, 5y ctrtala toAatd." The Utter liavc perianal by oxidation, but the two former nre found in great abundance in th e 6eldi and bogs in every part of Ireland." There artma nv varieties engraved illustrating the paper above alluded to, but none like the one in the Exolisii Mechanic. Perhups the usual fiat or cup terminations may be seen broken off.— D. T. Batty, 9, Fennell-strect, Manchester.

[3SD1.}—SLIDE VALVE.—I should not Uiink that "Slide Valve " would succeed with an engine having a cylinder leas than 3in. stroke, or l^in bore. The uywtuiel would require to be about 10in. diameter. I shall be happy to give him any further particulars.—Ixion.

[33940—IRI*II KIXG MOXEY.—In answer to "Dankoaen," I beg to inform him that it was used by the ancient Celtic inhabitants of Ireland. They are usually in the shape of a crescent, sometimes with and sometimes without pointed ends. The weights of some arc 53gr., ldwt. Sgr., and 4dwt. One, in the shape of a horse-shoe, weighed as much as 15dwt. "Dauboscn " is mistakes in supposing that they mav have formed links of gold chains; they are always alone, and complete in themselves. They must have been current monev, and not ornaments, because they exhibit no signs of attrition in places where they could have been worn. They arc, I believe, alwnvs made of the purest gold. Very little is known of these curious articles, but there is a short paper on them, with three illustrations, in the Numismatic Chronicle, old series, vol. vii. It is bv Edward Hoare, Esq., of Cork. From it I quote the following:—" A friend has suggested to me, and I think with great probability of truth, that it is possible that the crescentic form has been given to these Celtic rings with a religious protective view. The worship of the moon is an idolatry of the most ancient date, and the crescent form may have been adopted to preserve by its snered character, the circulating medium from spoliation or debasement, in like manner as the ancient Greeks impressed the images of their gods upon their coins, as it is believed by many, ia order to vouch for their purity and weight, and to vcure them from damage.—Henry W. Iienfrky, M.N. S-, &c.

[38500-TriERMOMETift.—If •' Thermometer "will take nil instrument by the end furthest from the bulb, and give it a good shake by swinging his arm, he will probably find all the mercury unite.—Ixion.

[3895.]—PARASITES ON CANARIES.—To cleanse the bird, tic a piece of unslaked lime about twice the size of a walnut.in a piece of coarse calico exactly aB a woman makes a blue-bag, leaving ends to it; dip it in water, and put it on the bottom of the cage. As the birds fly about, the fumes from the lime as it slakes penetrates betweeu the feathers, and cause the lice to drop from the bird. Keep the bag in about a week; it will not hnrt the birds. To clear the cages, Stc, make a strong solution of alum and water, wash the whole with it; this will kill the lice dead as stones, and is far better than lime-washing. The breeding-boxes can be dropped inte a pail containing alum solution for a few minutes, and then hung np wet as they are; it will not hurt the birds. Special attention should be paid to the moss, seed, and egg pans, as it is under these that the insects breed in the greatest numbers. This process can be repeated as often as hecrssary, and it is better to hare a spare cage to put the birds in while cleaning their own, if they are breeding. By paying attention to this the birds can be kept free from the pest.—A New Subscriber.

[3895.]—CANARIES.—The disease with which your canary is afflicted is a troublesome one, and if the cage is infested with vermin it is best not to use it again. Those parts of the bird where the vermin arc most likely to lurk should first be syringed with water in which a little quicksilver has been allowed to remain for some hours, or with a weak infusion of tobacco. Some recommend fumigation with this herb, but the inhalation of it by the bird, which can hardly be prevented, must prove prejudicial. Frequent bathing, great attention to cleanliness both as regards the cage and its inmate, and a daily supply of fresh sand, are also necessary to effect the ejectment of these troublesome visitors. A cage of which they have once taken possession is, however, never entirely freed from them; and it is best to get rid of it If you cannot do this, wash it often, sprinkle the joints and crevices with turpentine or a weak solution of white precipitate powder, taking care not to put the birds into it for some hours after the operation is done. With this solution als), should the vermin prove obstinate, the body of the bird may be washed at those parts which it cannot reach with its beak. —A Lovrb or Birds.

[3895.]—PARASITES ON CANARIES.—Some years ago I found that my birds were infested with those pests, and wasting flesh as though they had some disease. I tried several washes and powders, bat found none so good as the following:—Well soak the cages in water to loosen the dirt, then carefully scrub them inside and out, dry them, and drop a little paraffin oil into all the cracks and crevices. It there are any in the bird, hang a white cloth over the cage at night, and they will soon leave the cage for the cloth, when they may be shaken off in the morning.—J. H. P.

[3S96.]—LADDER PROBLEM.—I note that "Ignoramus " has not given the height of the man who has to go up the ladder for liis head to be level with spout; for a mau 5ft. 6in high, it would take a ladder 32ft. long; height where resting against wall, 21ft. from ground. For a man Oft. high, it would take a ladder 31ft. -fin.; height from ground where resting against wall, 20ft. tin.—J. Parke a, Swindon.

[39090-COPf'ER COIN.—No. 1 is a third brass, of Constantino the Great The full legend onobv. is VRBS ROMA. The rev. represents the tradition of Romulus and Remus, founders of Rome, suckled by a wolf, the letters T. R. P. in the exergue signifying, I think, Treveris Pecunia. No. 2 is not denned sufficiently for me to make out.—D. T. Batty, 9, Kenuell-street, Manchester. ^—*^911.]-GALVANTC CELL.-"Hermit*a" galvanic cell is the same as Bunsen's, and he should therefore use strong nitric acid for the porous cell, and a mixture of about 12 parts by measure of sulphuric acid to 100 parts water for the outer compartment. As the mixture last mentioned gives out great heat on mingling, it should not be prepared in a glass vessel. The cell will give good intensity but moderate constancy.— T. S. Conisbee.

[39110-GALVANIC CELL—In answer to "Hermit," two exciting fluids are required—one for the carbon and the other for the zinc. That for the carbon is undiluted nitric acid (aqua fortis), and for the zinc diluted sulphuric acid (1 part bv measure of the acid to 7 parts of water.) This battery (Bunsen's carbon) is very effective in use, and involves a current of considerable intcusity.—Electric.

[392H.] — MEASURING LIVE STOCK. — TO "A COUNTRYMAN."—Measure round the animal close behind the shoulder, then along the back from the fore part of the

shouUer blade to the bone ntthe tail. Multiply the square o'the girth by 5 times the length, both expressed in feet; divide the result bv 21, and von have the weight of the -1 quarters in stones of 141b. Thus, if the girth be fijt't., multiply bv G\, rhat gives 42 J ft.; then if the length be 5Jft„ multiply by '), making 26Jft.; next multiply the result 4ei J by 26J, and you

have 1109—ft.; this divided by 21 gives Mst. 111b. as nearly

IS as possible.—M. P. C. S.

[3020J—MEASURING LIVE STOCK—Among a host of memoranda I had the following rule, which may be of service to "A Countryman." Measure the girt close behind the shoulder, and the length from the fore-purt of the shoulderblade along the buck to the bone at the tail, which is in a vertical line with the buttock, both in feet. Multiply the aqunre of the girt, expressed in feet, by 5 times the length, and divide the product by 21; the quotient is the weight nearly of the 4 quarters in imperial stones of 141b. avoirdupoise. For example, if the girt be fllft. and the length 5Jft., we shall have 6J x &k = 421, a»d 5J x 5 = 26i; then 1 *

42$ x 261 = 1109—, and this divided by 21 gives 5216 S

stones nearly. It is to be observed, however, that in very fat cattle the 4 quarters will be about l-30th mare, while in those io a very lean state they will be I-20th less than the weight observed by the rule. The 4 quarters are little more than one-half the weight of the living anun.il; the skin weighing about the 18th part, and the tallow about a 12th part of the whule.—Harry G. Nkwton.

["Patience and Perseverance " has sent a similar reply.]

[3922.)—REMOVING PAINT.— " House Painter" can obtain at uhuoat any oilman's caustic paste, which is sold for the above purpose, but in my opinion burning off the old paint is the only safe method. If any solution be applied to destroy it, the wood will absorb sufficient to materially affect any coating afterwards laid on, and so render the result anything but satisfactory.—Harry O. Newton.

[39270— WINDOW-PAINTING.— Let "Sable" take of flux, which is formed thus — Glassof lead lib., of pearl-ashes 6oz., of common salt 2oz. Theglassof leai being reduced to a fine powder, and intimately combined with the other ingredients, the whole must be put into a crucible capable of returning vitrified bodies, and fused. The lower the heat by which the fusion can be accomplished the better; the operation should not, therefore, be hurried. When the mixture has beeome transparent and free from air-bubbles, it may be poured out upon a clean iron plate. If the composition, when cold, is observed to be very foul, it should be reduced to powder, and re-melted, but if only a few foul specks are observed, they may be picked out. The good part may then be reduced to powder and kept for use. This flux is moderately soft, and has a slight tinge of yellow. The glass of lead is prepared by fusing 2 parts of red lead with 1 part of Hints calcined, and finely levigated, or instead of Hints the finest white siliceous sand. Tiike of the above flux G parts of gold precipitated by tin 1 part; when these ingredients are thoroughly mixed they are ready for use. 'The colour thus prepared produces a fine crimson, inclining to purple; its strength may be increased by adding more of the oxide of gold. For the yellow, take of the above flax 6 parts, of calcined silver 2 parts, atd of antimony \ part. Vitrify them, and then levigate them for use. The colour is a deep bright yellow proper for shades; where great transparency is wanted the antimony may be omitted. The silver is prepared by covering thin plates of silver with sulphur, and exposing them to a red heat. If sulphate of iron be dissolved ic water and precipitated by pearl-ash, this precipitate, used instead of antimony, will produce a very cool and true yellow, proper forming greens with blue.—D. F. Ashton.

,[3931.]—INDIA RUBBER SOLUTION.—It may be made with vurinus solvents—turpentine, chloroform, benzole, 8tc.; but the best is, I believe, a mixture of 6 parts alcohol (absolute, not mere spirits of wine; with 100 of sulphate of carbon; the latter is the real solvent, the alcohol has an indirect action. The quantity of solvent required depends on the consistency of solution required ; if heat (moderate} is used, and the mixture shaken, the whole dissolves, bat a better solution is obtained for adhesive properties by using a large quantity of solvent, not shaking, but drawing off only the clear glazy liquid.—Sigma.

[3931.]—SILK SOLVENTS.—Several substances dissolve silk, such as the amraoniacal solution of oxide of nickel; that of copper also dissolves silk as well as cotton: the silk is precipitated by acids. Chloride of zinc saturated with zinc oxide also dissolves Bilk, but in no case can silk thread be dissolved without the "thread being decomposed," for solution of course involves the destruction of the mechanical constitution.—Sigma.

[3937.J—CHEMICAL QUERY.—See "Urban's " letter.

[3937]—CHEMICAL QUERY.—As liquid nitrous oxide raised to a gas at 0°C. and 700mm. ia just at the normal condition for calculating gases, it ia only necessary to divide the 200grms. by thf* weightof a litre of the gas, which mav be calculated off h\drogen as follows:—As a litre of H = 089Ggrms.; therefore a litre of ONa (density 22) = -0S9G x ■& 200grms.

Consequently = 101*46 litres, the answer

•0666 x 22 required.—Night Schoolboy.

[39410-MARKING INK.—If" Daisy "put the ink on a piece of velvet, and then rubbed it over the types (or to glue it round a roller would be better), I think he would succeed. I have used the ordinary writing-ink that way, and found it succeed.— PaiKTF.o,

[3943.]—BEES.— For simplicity there is nothing like "Payne's Bee Hook." He was a really practical apiarian at Bury St. Edmunds, and loved the old straw hive, but never destroyed a bee, nor allowed them to swarm unless he pleased. —Anom.

[3950.]—GOMUTU FIBRE—The Gomutu palm ii the sugar palm, Arrnga sacckarifera, La bill, occurring in great abundance in a wild state throughout the islands of the Indian Archipelago, and cultivated generally by the various people who inhabit this region. The Malays call the tree "anou;" the liquor (toddy; obtained from it "tonak," or "nem ;" the horsehair-like material covering the base of the petioles "EdjH," or "Gomutu;" the Portuguese call the tree "Saguero," "sago tree," or "Sagwire," The fibrous substance of the base of the petioles—superior in quality and cheapness to coir or cocoa-nut fibre, is used by the natives for every purpose ol cordage. The coarsest parts are used aB pens by all the natives who write, and also as arrows tor their blowpipes. 1 do not find any mention of these fibres being employed for brooms or brashes. Cabo negro is, according to

th- SpHiiish Catalogue of the Paris ExtubiUoo, i*e u**given to the tree by the Spaniards of Manilla. Mora pm/teat»rs, riJe "Sec man's Popular History of the I'iijsat," ^&i many other works. Tus coarse obocolate-oduured fibm used for making the brooms for sweeping the sired*. t±r decks of ships, ike, and also employed for Withworthswt-e^Ha?machincs, come from the Piacaba pnlnu At taUa fvnifmi, <&j arc imported in England from Bahia; a finer sort enssr^ from Pari is produced by another palm tree. ^£^9«cv Piacaba, which I find in an horticultural catala-gtic skM "Lropolditta Piacaba vera," the Attalea funif'era fteissj ssa known by gardeners as Ltopohli*a piacaba. The iutrt^m-tt of Para piacoha into industry was an example monof^* application of a simple observation, a bundle har^j^, made up at Para for a vessel, to let down of the bal-nAs u "fender," to prevent collision, &c. The ship arrr^ c Liverpool the bundle was thrown upon the quay; t ^raftmaker took it and made a few braahee from it■ they v*r> found to answer well; a small quantity more vaj ituportH. and the trade began. It was formerly imported as •"Manage," but orders having increased, piaenb* ia now impart-j from Bahia and Para on freight. A price current I h-,-» before me quotes Bahia fibre 12s., and Para do. 65s. per e**.. The nuts of the AtUden font/era, or "Coquilla ones'* u? used for turner's work.—Bekhardtiv.

[3954]— SCRKWING LATHE. — If P. N. Haalari tires near London be had better get my address from Ut Editor, and come and see my lathe, from which he may fia, hint or two worth haviug. 1. The length and Ureadti Lr mentions will do. 2. A screw such as I have juat maxL? k* my 5* lathe—viz. f diam.. double V thread, fc pitch, will ssA.

1 have in now a screw of 10 to an inch, and this is to take iu place. 1: should not bo inside, as it is sure to get din* wherever it ia, and is much easier to clean if outside, **4 hence likelier to get kept clean. 3. A j nose of Wbitworta » thread will do very welL 4. Geared lathes are generalir made 2 pair of wheels or pi nions of 3 to 1, giving a re d action of speed to l-9th; this I think much too great for a sffia ;1 lathe, and I have made, or hid m ide, sever il, and am Ojt making a 5* for my own use, with wheels of S to 1 Uj front of pulley, and 2 to 1 behind the pulley, giving * reduction to l-6th of speed. I have by me a set for t 44Jn. lathe of 3 to 1, and 2 to 1, or a reduction of J. Ttj numbers suitable are 72 and 21 for the front and 4* and Si behind, both of the same size ef teeth which in nn case is to be nearly No. 9 on the Manchester guage, gtrin» the Ti wheelfl* diam. by f thick, and the other pair only } thick as the strain on them is less. The teeth are t<> be cot in gun-metal. If you have cart wheels 60 and 20 on the So. 8 gnage give distance of centres of mandrels 5m., and a puller* of 7J, which you will hardly get into a H head, and the 10 guuge gives a 6}in. pulley, which in too small. Perhaps Lloyd may have gear wheels specially for 4J Jathe bv him. Mine are 66 and 33on the 10 guage, and are in Lloyd's handa, with liberty to cast from them. S. I should not advise self-" acting surfacing, which 1 do with a band from overhead. I should make the bottom slide project over the rear side of bed

2 or Mn. in addition to the ordinary length The last I made was a 44one, and the bottom slide measured 10$, and I was sorry I had not made it 12'before I had done it. The tap one may run 4in. more or teas. The best tool holder swivels round on a centre bolt, and is of square shape supported under two of the corners by a couple of pillars, and has sot screws attached tapped down through the other two corners, which are provided with bosses for the purpose. 6. You cannot wish for a better wheel cutter than mine figured in So. 215 of the English Mechanic. If you use a diviujug-piate with holes, it should be 4 times the diam. of the wheel to be cut, or more if possible. (See p. 4t of present vol. for some remarks on dividing pegs.)—J. K. P.

[3955.]^SC.\LE PARAFFIN.—I should think the quantity of scale paraflln produced last year lin Scotland) would be about 1500 tons— RzrisiEB. [3956.J-WEIGHT Or GAS.—See G. E. Davis's letter. [3957]-POWERS OF NUMBERS.—I believe the easiest way is to make use of the formula log. (an) — n log. a; for

3 example, if we have to calculate x = —, I put log. x =

5 3 3

I03. 10- = — log. 10 = 0-60000, and I find that 0*00000

5 6

is very nearly the logarithms of 0 30-32; thus X = 0 3953.

—BfcB.NAB.nilf,

[396-1]—CAST IRON.—Chipping is as much an art, and to be done really well requires practice as much as filing does. Any smith any where will draw you out a chisel and show you how to use it. The steel generally used is either octagon rolled for the purpose, or round, flattened on the sides. I keep an earthenware pan in the garden, and put a casting into the acid water left from last time, and then pour in strong sulphuric acid, till I see the hydrogen come away freely, and leave it for 12 hours. This will bring most of the sand away. I think the best stuff to nuike casts of for electrotyping is white wax with a lot of rottenstone molted up will*, it. The powder makes the cast hard, prevents it shrinking so much, and makes it heavy enough to sink in water; it blackleads very well too.—J. K. P.

[3967.]—MAGNETIC NEEDLE.—In a vertical galvanometer the strong needle would give the greatest deflection; in a horizontal galvanometer there would be a slight difference, as botu the forces would diminish alike by the weakened mugnetism; the difference really found would be due not to the magnetic difference, but to the relation of the actual deflecting force to the weight of the needle—*. e., its inertia, and to the friction on its support. In my own experiments I have found that with everything thesame in other respects. different needles give different deflections, but the same needle weakly or strongly magnetised gives tho same- — Sigma.

PAINTING WOODEN PAILS—The practice of painting the inside of wooden palls, to prevent leakage, Is only to be recommended when tho paint contains 119 white lead or baryta, both of which wo found In the paint of some pails examined lately. All over the country these pails are used in tne kitchen, and nlthou-jh either lead or baryta are noi very noluble In water, yet frequently the paint peels off In Hakes, and may have serlcus consequences when getting into the teakettle, and thus into the food. Tho paint for such purposes should be either whiting or gypsum, If required white, but the most preferable Is ochre, against which the sanitary objection cannot be raised.

BOTES AND QUERIES.

[3971]-IKON STAINS.—Could some brother reader tell me what will reraore iron stains from linen or calico? The question has been asked before^but never answered.^. H. P.

[S973]—A WATER VELOCIPEDE.—Noticing that you have taken ereat interest in vottr journal in the velocipede movement, Fnmke free to ask if you can tell me where I can ■»pt a water velocipede. I have recently lost my nt;tit arm so am debarred from taking part in most outdoor amusements.—J. D.

t397t.]-BOBHM FLUTE.—Would H. T. Leftwieh kuidlv give a detailed working account of the "equiionant 4at<; " also where it can be obtained, and if it is much more «pvnsi»e t)un the old flute? Can lie or any other reader say where I could obtain kevs and 9ttins;s for the same and other description of flutes cheap.—AttornKlidtist.

£3975.]— VALUE Or" COIN.—Can any reader tell me the value of a coin in nry possession, of which I send a sketch?

[graphic]

The characters are roughly formed and raised. It is, I believe. silver — IlAKaT G. Newton.

[397O0-BRITTLE IND1ARUBBER.—I observe that ■heets of vulcanised indiarubber become brittle after sime time ; what mar be the cause of this? Is there any means of preventing it?—Caoutchouc.

[S9770—BRAZILIAN RAILWAYS.—To what extent are the different railways diverging from Bahia in activity? Are the constructions advancing?—H. Z- Y.

[S9780—ROUND ZINC WIRE — Is round zinc wire manuactured so small as No. 2i, B W. G.? I have tried several wire mills, but cunnot get it.—Thkohiim.

[3079-3—BRICX9 AND POTTERY.—Will any reader tell me of a good practical work on pottery from which I could gai n a knowledge of the different operations curried on in the potter's art; or a good book on brickmaking? I have Mr. Dobson's work, published by Virtue, Bros., which is a a capital rudimentary treatise, but I should like something larger, with more detail, if possible.—Old Subscriber.

[3980.]—CLINTON'S FLUTE.— I hope Mr. LeRwieh wtl be so kind as to accept our Editor's offer. I sec he recom-1 mends Clinton's flute. Has he ever tried Carte's improved Boehm flute.—J. H. M.

[3931.]— BOOKS.— Will any reader iuform me in your next publication of the English Mechanic if he knows whether there is a book published that gives the weight of different sizes and lengths of iron, viz., rounds, squares, fluts, Use., nl(owing for heating, rolling, and crooping, the name of it, and where it can be bought? Or can yon recommend a book to assist a mill manager iu his work, oue with tables giving the weight of the pile to produce finished bars? An answer through your valuable journal will oblige.—L. M.

[394*2.]— WORKS ON SOAP MAKING,—Cunld any of our readers give me the names of the authors and publishers of any good practical books on the above subject? Also, if they could refer me to any periodical or journal where good papers or articles hare appeared on the subject?—M. G. Morgan.

[3983.]—ENGINE INDICATING.—If some one of our excellent correspondents could kindly give me a little instruction on engine indicating I should feel greatly obliged. I have heard of one young man in this neighbourhood who is giving as much as 5a a lesson for instruction on the subject, 1 believe it would be interesting to many of our readers. What I want to know is, how to take a diagram, then how to measure it up so as to get the power; and how 1 must get the pressure per square inch? The diagram before me is divided into 40 lines, and every tifth liue is extended to the margin and marked " Atmospheric 5, 10, 16, 24"upwards, and the same downwards, but tbe fifteenth line downwards is marked " Vacuum." I should be glad of an explanation, and also wish to hear of a good book ou the subject.—Vacuum.

[3984.]—ALUMINIUM BRONZE—I shall feel obliged if any of your readers can inform *ne of the proportions used in the mixture of aluminium bronxe.—Aluminium.

[3985.]—FLEXIBLE PIPE- Would any reader inform mc if there is any flexible pipe that will stand boiling water, or if indinrubber canvas hose pipe would answer the purpose? —

[39&8/J-CYANIDES.—TO "SIGMA."—Would "Sigma" aay where I can get the latest information about the manufacture of cyanides from the combustion or heating of char, coal with nitrogen and potash; also if soda-barytea, &c. have as good effect as the potash ?—J. W.

[S987.3-OIL TESTING MACHINE.-I use a great deal of oil for lubricating purposes, and 1 have observed in your journal some time since an advertisement of an oil testing machine Can any of yonr readers inform me the machines that are now generally approved for that purpose?—Vfu. 3 onus.

[3988.]-STUFFED BIRDS.—I have 37 Australian birds which I want set up in case with glass front. The case is 4ft by 3£ft. and 13* deep. The birds vary in size from magpie to humming bird. I should like to construct an artificial tree, but don't know how to proceed. If any kind friend would give me sketch of tree and instructions how to make it through yonr valuable paper, he would extremely oblige— One In A Fix.

[39890-SCREW ENGINE FOR CANOE—How large a strew engine with double cvliuders ought one to have to drive a c^noe 15ft. long and about 2jft. wide; also size and •nape of boiler; alto about what price i/I buy them?—A

YoUNfl Sl'BSCMBstB.

t.W90.)-YELLOW DYE.—Will any reader fell mc how to make a deep yellow dye that will stand the uir ?—A Counts! lias.

[39910-DARK LINES IN SOLAR SPECTRA.-Will "T. A." say how, according to his atmospheric hypothesis, he accounts Tor the dark lines in the spectra of the fixed stars; they being totally different from the solar spectrum and from each other? If the amount of iron, for instance, necessary to produce the iron lines in the solar spectrum is, as he says, contained in our atmosphere, and continually falling to the earth, is it more than probable that the Bunaen burner would give some indication of it in the same way as it doesof sodium?—Stkkksman.

[3992]-SIZES OF ROPES.—Having road with pleasure the article on "Strength of Materials," bearing as it does on my own trade, I should feel obliged if anv one could inform me if there is anv published tables of the number of threads and strands for given sizes of circumference and diameter of ropes from the smallest to the largest sixes ?—Anxious To

[3993 ]-PASSAGE TO NATAL,—Will anyone inform mc through the Mbcuamc the best and cheapest way to get to Natal, South Africa.—A Cobnish Max.

[3994.] —ELECTRIC MOTOR FOR SEWING MACHINE— I see from n back number of" All the Year Round" that a Frenchman, Mons. H. Cayal has invented an electric motor for working a sewing machine. I should be much obliged to any one who will give me some particulars about it?—J. H. Mrrivalb, Ealing.

[3995]—BOOKWORMS.—Can some reader inform me what will effectually destroy bookworms without injuring the books?—Bookworm.

[39901— BOOKBINDING.—Will any of our numerous subscribers tell me whether brass type or handle letters will be best for me (an amateur bookbinder) for gildjng letters on the covers of books, also the price of leather per skin, and cloth for bookbinding per yard ?—Q- Yorkshire.

[39970—ARTIFICIAL FOUNTAIN.—I wish to make an artificial fountain, the same as seen in watchmakers windows occasionally, where a glass rod is made to revolve. I have the movement of an old watch, and 3 small cog-wheels, hut I cannot manage to fix it iu any way. Would some kind friend give me a few hints?—T. P.

[3998.]—ORGAN MOVEMENT TO HARMON IUM.-I have made a harmonium with two rows of reeds. Will "Lever" or any other tell me howl can put thoorgnn movements on. I see on my catalogue that I can get the full organ movements for 3s. 6d. Could any one tell me what they are, and how they are fitted on?—Young Amateur.

[39990-CYLINDER.—Will any reader be kind enough to give me the dimensions of cylinders for small steam carnage? — Ixinw.

[4000.]—SODA WATER.—Will any brother reader be so kind as to inform mc how to test a very small quantity of tartaric acid in a tumbler of water from citric or vice verso One In A Fix.

r400t]-ATMOSPHERICINFLUENCE ON ELECTRIC CLOCKS—Has the atmosphere any influence on electric elocks?—Elbctbic.

[4002.]—MUSLIN DRESS.—I have a muslin dress, originally a bright violet, hut now very much faded. Will any of your numerous correspondents kindly inform me either how to extract the colour entirely, or to rostore it'r—Bkta.

[4003]—WATERING GARDEN.—Will anyone kindly inform me of the easiest and cheapest plan for raising water and watering a garden, aay 20yd. lon<? The river runs close to the garden, hut is ahout 8ft. lower than the level of the ground." Something of the force-pump style, but less expensive ?—F. H. Joxks.

[4O04]-SFECTROSCOPE.— Will "F.R.A.S."kindly give us another paper describing " some rude and makeshift apparatus by means of which rudimentary spectroscopic observations might be made," as it would be very acceptable to many of his renders. Also will be Bay whether solutionsof sodium, salts, Sec, will give absorbtion bands if placed between the lamp and slit of the spectroscope; if so, will he tell us which solutions will give us the most striking results as experiments? I hope he will do what he intended in relation to Sirius, as I am sure the Editor will nut deny him as much space as- he likes for what is interesting to so many of his readers.—U. W. Bishop.

[40050-GUN BARRELS.—I should feel much obliged if anyone will tell me how to clean the inside of gun barrels in the lathe, so as to make them look like the gunsmiths do ?— A New Subscriber.

[4006.]—DRESSING STONE.—Can any reader inform mc whether there is in operation anv machinery for working or dressing the hard grit Btone such as is used in the buildings of Lancashire and Yorkshire.—Stonemason.

[4007.]— CURING HERRINGS.—Will you kindly allow me to ask if any of your readers will tell me the way to cure herrings, or name any book giving such information.—J. Baskkkvillk.

[4008]—GRAINING STUFF.—What is the colour made of that grainers use for oak grain, not the ground colour, but that over it.—J. Baskeryillk.

[4000.]-HEATING BOILERS WITH GAS.—Will some brother reader give some information respecting heating steam boilers with gas. I Relieve they require very little attention, and can be kept in readiness for work l>v turning on sufficient gas to keep the water boiling. I think also that insupance companies do not charge extra premium where these boilers are erected. These are certainly very great recommendations if there are no corresponding drawbacks. I had thought an ordinary vertical boiler would answer if the furnace bars were removed, and gas pipes put in. I should think the flues ought to be smaller. Possibly one tube bent into a spiral form running from bottom to top would give good heating surface, and be sufficient to carry off the products of combustion. I should like to know also whether there is any objection to feeding a boiler with boiling water; it seems to me it must require a deal less tire iu the furnace to raise the same amount ot steam.—Cobn Factok.

[4"100—MELTING AND CASTING METAL.—Would some experienced reader be kind enough to assist me in the melting iind easting of a metal si- ilar to printers type metal, but much harder when cast, I want to get a nice clean sharp cast of designs 1 have, the moulds of which are of iron and brass, and will make a cast about '.'in. square and about gin. thick. I have tried zinc, tin, and other metals, hut without success. 1 should like to know the exact proportions of metals to mix to get what I want, and whether it should be melted in a ladle or crucible, and how to tell when hot enough, and if anything should be put on the mould to assist tbe sharpness of the cast; in fact anything that would be necessury lor anyone ignorant of the process to know would be most thankfully received.—A Bristol Amateur.

[tOllO—PRICKING BARRELS OF BARREL ORGANS. —Would "Adept" or any other subscriber kindly describe in detail the process of pricking the tunes on the barrels of mechanical organs? I should be very greatly obliged forauch instructions as would enable me to set out tnncs and overtures on tbe barrels of an orgnn having a complete scale, and working its own stops.—Pupil.

[4012.]—WORM-EATEN ORGAN BARRELS.—Can any one inform me what would prevent dry wood from being worm-eaten (weevils I think they are called)? Some of my organ barrels are becoming completely honeycombed by these troublesome creatures, and I should be glad to know if there is any solution which will kill, or prevent them from doing further mischief.—Pupil.

14013.]—TO N. S. HEINEKKN.—Would N. S. Heineken kindly state the price of" Le Manuel du Facteur d'Orgues," and where in London or Paris it could be obtained? Also state if it gives practical instruction in organ building?— Pupil.

[4014.]—MEDICAL ELECTRICITY—Will one of our knowing friends kindly answer one or two questions:—I. I have seen it stated that a current from a secondary is of no use for medical purposes; but onlv that from the primary wire—Is it so? S. Will an induced current induce a current in a coil laid on the second? I have Been a beautiful little apparatus made by " Rosenbloom " (I think that is the name) the current of which might be modified in a most simple and beautiful manner. On the baseboard there were a number of brass studs, numbered from 0 to 16, placed in the form of two arcs. These communicated under the board with fine wires from the coil. Attached to bindiug screws were two brass movable arms which, on being placed on corresponding studs, would vary the power of the current. When placed ou studs No. 0, it was so gentle that a child could bear it with pleasure; but when moved to the highest number, it would be sufficient for several adulta. A friend of mine who has one has been very successful in relieving many obstinate coses of contraction of limbs, rheumatics, &c. Now I think if an affirmative can he given to both my questions, then an apparatus with various shades of power can be easily made by coils of various lengths laid on each other, their ends communicating with the corresponding studs. I may just aay the coil was. worked with a single pair of plates C and Z, the C about lin. by 3, the Z in the form of u U. »o that each aide of the C was used—O'Bac.

[4C15.J- ARTS EXAMINATION, ROYAL COLLEGE OF SURGEONS.—Will some brother reader who has passed the above kindly inform me what is the minimum nuniucr of marks, and how soon one is informed if he has passed?— Gaddiia.

[4016.]—ARMY COMMISSIONS.-Will anyone informme through the Mechanic what is the limit of age for purchasing commissions in tire line regiments? On referring to the Array Regulations I find 17 to be the earliest age at which a commission cau be held, hut it gives no other limit. For men it is 18 to 45, what is it for officers?—Linesman.

[4017.]—CRICKET BATS.—Would some ol my brother readers versed in the manufacture of cricket bats kindly give some information as to what kinds of wood are used for the purpose; also how made -, tbo respective merits peculiar to each kind of wood; in short, any information that will guide a lover of cricket in making his own bate?—Stump.

[4018]—ISOMETRICAL DRAWING.—The eense of my query (31*23) waa loBt last week by the substitution of the word " geometrical " for " isometrical." Readers who intend to favour me with a reply will kindly notice this correction.— C. J. II. Cotthesow.

[4019.}—SAFETY VALVE.— I want to have 201b. pressure on the square inch of a boiler, tbe length of which is 1 lin. long by Oin. nroad, and 4in. high. Would "Jonalli " kiudly give me the rule for hading the size of safety valve, length of lever, &c?~0. G.

[4020.]—WOULFFE'S BOTTLE.—I have a 3-necked WoulflVs bottle, but in two of the necks the glass has not been taken out in the inside so it is of no use. How can I take the glass out without injuring the other part of the bottle? Would a common diamond do to scratch it, and could the glass be then kuocked out ? - M P.C.S.

[4021.]—COINS.— Will some brother reader inform mo what the following coins are, and their relative value? A coin (silver) slightlv larger than a sixpence. Obv: female bust—Anno. Dei. Gratia. Rev: 1777 Mug, Bn. Fret. Hid. Reg. with large cross. Another the same in circumference, but thinner than a shill-ng. Obv: (1 take it) CAROLV3. VI. D.G. ROM. IMF. SEMP. AV3. with double-headed griffin with mace and asword, I.h.l. in small capitals. Kev.^Castle

with wreath around, and below a circle with gcHlLL

inside. Around margin, Hamburger. Current 1725.— Yblock.

[4032.]-TUNING BELLOWS FOR HARMONIUM REEDS, &c—If our talented correspondent "Elcve" will answer the following questions I should feel grateful:—1st. Which way must I set about to make a pair of tuning bellows that will answer for tuning any size reeds, or where could I purchase one similar to those used in large establishments? 2nd, What sort of "holders" to hold the reeds (any sire) during vibration? 3rd. What construction of belluws to keep a continual vibration at pleasure without breaking off the wicd? Would a couple of bellows answer, one to go up while the other is going down? Details with diagrams would oblige. —reed Tuner.

[4033.J—ORGAN STOPS.—Will the "Harmonious Blacksmith" or " Adept" please give an opinion on the following? I am about to build myselfa small organ with about 4 stops, which stops would suit best? I have thought of open diapason, slopped, principal, aud fifteenth, or would a flute iu place of fifteenth answer better —Jos. B. Crosslky.

[40240-GALVANISING CAST IRON—Would any of your readers kiudly explain the process of galvanising cast iron. Mr, Meredith in oue of your "replies" says the process is the same as for wrought iron; but not- knowing tho process 1 am compelled to trouble you again ?—B. Wkbb.

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