SEPT. 9, 1870.] ENGLISH MECHANIC AND MIRROR OF SCIENCE. through the first separator, passing through the scourer, Science" implies (p. 548), I call it a most balls, or other light substances, the other, after cleaning balance.-SERGIUS.) B Sub [4484.]-BUNSEN'S BATTERY.-" An Old [4409.]-FOUL AIR.-It is a most mischievous error to suppose that wherever a light will burn a man can live. A candle would burn to its end in plenty of giseous mixtures that would be instant death to any Warm-blooded animal entering them. No man should be allowed to descend into a well, a liquor-vat, or any pace left for many hours without downward outlet, till a bird in a cage has been lowered for some minutes and drawn up alive. The only reason why ascending into an [4495.]-GOLD SHELLS.-These may be made by rubbing up gold leaf with thin gum water and spreading upon shells. The gum used for this and colour grinding should be the finest white gum arabic dissolved in distilled water. The palate knife should touch this and all the mineral colours, especially the vermillion, as little as possible. Beware of dust in all such operations.-SABLE. 595 was doubtless occasioned by a current of hot air rising from the roof.-UNIT. [4519.] PHOTOGRAPHY.- Ordinary shellac dissolved in spirits of wine makes a good and cheap negative varnish, to be poured on to the warmed plate the same as collodion. Or the hard spirit varnish, made for carriage painters, diluted with twice its quantity of spirits of wine, is good.-UNIT. [4521.]-EXTRACTING HONEY FROM THE COMB. -The method I adopt is to stretch a coarse strainer over the top of an earthen pan, open the cells of the comb with a knife, and cut the comb into pieces. Then place it on the strainer, when it will drain into the pan beneath perfectly clear. This is the most simple and the most perfect plan I know of.-WINNER. [4585.]-HORTICULTURAL.-"G. H." in pruning gooseberry and currant bushes must be guided by the strength of the soil. At any rate, all main branches that crowd one another should be thinned out, and only as many left as the root can supply. After reducing the shoots down to spurs about an inch long, of course remain stems, take each one separately and cut the side moving all weak and spindling shoots.-SAUL RYMEA. [4539.]-CHIMNEYS.-In reply to the inquiry of Mr. Moody in your journal of the 19th inst. (query 4539), I beg to give him below the principal dimensions of a very elegant and efficient chimney-shaft erected for four (eventually for six) boilers of about the same size each as those described by him. The chimney is built of brick; foundation and plinth four =, and equal-sided; shaft octagon, in horizontal section. The foundation is 264ft. deep, forming an equal four equal-sided prism of 14ft. 8in. side. The plinth is 19ft. 8in. high by 114ft. side. The shaft is 92ft. high from top of plinth, so that the total height from ground-level is 111ft. 8in. The width of flue at base is 59in., and at top 89 in. The thickness of masonry in plinth is 39 in. and in the shaft at lower end 29 in. and at top 10. Plinth and shaft is cagped with hewn freestone. The canal from boilers leading into base of chimney is immediately under ground-level, and is 5ft. 6in. high by 4ft. lin. wide.-E. W. A., Cologne. [4501.]-SEWING MACHINES.-As "J. G.'s" reply [4541.]-EMBROIDERING MACHINE.-There is a machine special for this, but very dear. There are attachments for the same purpose to some makes of "Wheeler & Wilson," also to" Singer's," and perhaps the "Weed," and the "Howe." Bradbury's W. W. makes, so I understand, six different stitches; ranging from single thread chain stitch to eight thread embroidery. Seller's W. W. uses up to five thread embroidery stitch. I consider the "Gulph" treadle the best chain stitch machine. Perhaps it would suit "A Braider," but chain stitch is not embroidery stitch.AQUILLUS. [4545.]-SECRET CODES.-In compliance with the request of "Argus," I send you the clue to the "secret code" upon which I commented in your columns in No. 278. To take the simplest case, let us suppose that the suspected word is the first in the cipher, and is believed to be BEACH; the corresponding letters in the cryptograph being ULOTU.-We proceed as follows:-1st. Write down the alphabet in order as far as the lowest letter in the word-i.e., as far as H-and draw under it as many parallel lines as in the suspected word. 2nd. On the first line place U under B, on the second L under E, the last U under H-i.e., the cypher letters, one in each on the third O under A, on the fourth T under C, and on line, under the suspected letters. 3rd. Complete these lines in retrogradealphabetical order towards the left as far as the column under A, and the first column gives the key. Thus ABCDEFGH &c. TU &c. HIJKL &c. O &c. [4504.]-ELLIPSES.-The common trammel (or ellip; tical compass) has been described and figured several times in the ENGLISH MECHANIC, better than by T. W. Boord in this number (p. 548). Thus, in vol. VII. alone, I find it rightly figured by" Novice Barnsley," p. 193, as well as the still simpler mode of striking ellipses by foci and cord, three times given, pp. 148, 149, 214; and a third method on a wholly different principle, p. 452. Moreover the "connecting-rod" oval that our present "J. K. P." patronizes, is there also confounded with an ellipse, or an" ellipse in perspective," pp. 237, 323, and its first introducer, Thomas Arnall, even calls his inmust surely see that if it be ever egg-shaped, it must strument for striking it an "elliptograph." "J. K. P." always be unsymmetrial and a more complex curve than the ellipse, however, long his connecting rod. In fact, it is an oval of the fourth order, while ellipses and all conic sections are of the second, the same order as a circle. T. W. Boord's figure of the trammel has been made puzzling by the printer inverting it, but is also wrong by having the arms of the cross unequal; and an attempt to disguise the inherent defect of that instrument which is, that owing to equal length of grooves being required each way, you cannot strike any ellipse with a minor axis less than the width of the cross, nor can you strike one much wider than the instrument, nor so long as twice its width. In fact, only ellipses of small excentricity can be drawn by it, and the larger the less halving the entire cross, we can draw any ellipses not elliptic, by suppressing one arm, however, or rather exceeding its width, however narrow, by half at a time. "J. K. P." says this is necessary with Cowper's Ellipsograph, which I do not know. I greatly doubt the possibility (without very complex machinery) of striking any of more than small excentricity with ink and a drawingpen; though it is perfectly easy with pencil. The drawing-pen introduces difficulties that I long ago, though constantly drawing ellipses, decided to regard as not worth solving.-E. L. G. untried upward well, or place without upward outlet, E. L. G. [4415.]-CURIOUS PROBLEM.-According to the answers received from various sources it would appear that an "irresistible" force cannot co-exist with an "immovable" body and vice versa: in other words, these terms are incorrect, and as definitions of things which have no existence should be crossed out of the dictionary, or at all events become obsolete. To avoid such a conclusion my alter ego suggests that an "irresistible" force coming into contact with an "immovable" object would "make a hole through it !"-SAUL RYMEA. RST &c. Showing the key-word to be THORN. In the second case, suppose that the word is not the first, or that the sentence begins "The beach." Our first, second, and third trial will fail, but the fourth will produce this resultcipher being SRTJV [4511.]-WEIGHT OF BALL.-The length of wire length of wire = = = 3658 in. =304ft. 10 in. [4474.]-HORSE POWER.-"Vertumnus" (p. 548), [4481]-THE BAROMETER "DIFFICULTY."-I was aware that standard barometers have a movable scale ending downwards in the point mentioned by " A. M. W." (p. 571), and by thus separately measuring the difference of level at every reading, we eliminate the effects of any inequality of bore in different parts of the tube or cistern. But if this is expected to be done with every barometer, as "Exhibitioner at Royal College of ABCDEFGH... RS NOPQR... T HIJ OPQRSTUV... which gives RNTHO as key-word, which by an easy plying the cube of the diameter in inches by 186 for cast [4515.]-FELT HATS.-I cleaned my felt hat with "Easily written, easily read, Easily carried about in the head." To conclude for the present, as an old rhyme says, a smoothly and with moderate pressure, and the gold will [4556.]-TELEGRAPHY.-Nearly all telegraph-posts have now lightning-conductors, they have also "guards" to retain the wire from falling and coming into contact with other wires in case of an insulator being broken. It is probably the former "Mus" is inquiring about.UNIT. [4559.]-HORSE-POWER OF BOILERS.-Find the area of water surface freely exposed for the evolution of steam by multiplying the length of the boiler by the length of surface line, measured across the glass gauge, which in this case should be at least 6ft.; divide this Consequently Note. The absolute value in horse-power of 1 cube foot = 28 cube feet, allowing 1 cube foot of water to each square foot of = Consequently 14000 = 60 × 60 3.9 cube feet per second. and 3.9 x 10:46 40-78 H.P. also.-R. D. [See also letter headed "Boiler Power" in this number.] [4561.]—ENGRAVING BRASS PLATES.-Make the plates hot enough to melt red, black, or any other Chip it off the surface, where not required, when cold.— UNIT. [4588.]-TELESCOPE.-Varnishing the inside of the tube with a dead black will no doubt improve the definition of the telescope.-UNIT. [4589.]-TENDER FEET.-The "Pedestrian" should rub the inside of his socks with yellow soap, and wash his feet every other day in warin solution of common salt, and he would not complain of tender feet.-MED CUS. nearly colourless scales, when quite pure, but may 14605.]-PROPELLING A VESSEL B [4583.]-TENDER FEET.-On long pedestrian tours guide-lines, in order to sail as ships do within try [4605.]-PROPELLING A VESSEL BY A VA coloured sealing-wax that may be desired, and run it in dalis, red double daisy, all of which are compact little off the cap, and with a file open the wind-way a little. [4568.]-WEIGHT OF RAILS.- "Ferrum" should multiply the cross section of his rails or Tee-iron by 3-3 for iron, and by 3-4 if for steel, which will give him the weight of a lineal foot in pounds, and multiplying that by the length of the rail in feet will give him its weight. -G. B. D. 46 [4569.]-ESCAPE OF GAS.-It is a fact that when any holder is left undisturbed (viz., the inlet and outlet closed with water) for some time, that the gas will diminish in bulk. "W. C.'s" holder having stood so for nearly six months, I am not surprised at his loss. I send three practical reasons, which, taken together, will quite account for it. 1st. Is the holder thoroughly coated with good paint? If not, a large item is accounted for, as it is well known that gas will escape from one not painted, allowing that the joints are perfectly sound. 2nd. The holder has been exposed to the full heat of summer. The heat of the sun causes the gas to expand, thereby drawing the holder up," causing it to " blow.'" 3rd. I will venture to say that there is a quantity of oily matter floating on the surface of the water inside, if it has not yet shown itself outside. Gas consists of hydrogen and carbon, holding in suspension a number of condensable hydro-carbons, which by the varied changes of temperature, would be condensed, and form the oily substance above-named, thereby causing a diminution of volume. Were I acquainted with the size and situation of "W. C.'s" holder, and furnished with an answer regarding the first reason, I might write with more certainty; as it is, I only send the above facts for his consideration.-H. N. H. [4572.]-GEOLOGICAL.-"Philosopher" does not give sufficient data to enable one to answer his query with certainty. Malvern lies on the edge of a long narrow strip of Silurian rocks; so his limestone is probably of that age. If he can obtain any fossils from the quarry, they would tell him what formation they belong to. The Ordnance geological map of that locality is published in quarter sheets, and would not cost much, and will give the fullest information.-E. D. [4573.]-METHYLATED SPIRIT.-There is never any difference made in the quantity of wood spirit added to the spirit of wine. As to its quality, by which I presume "M. M." refers to its odour, that may at times vary, being dependent upon its rectification and the heat at which it was originally distilled. The wood spirit must be obtained from the revenue stores.-A, REVENUE OFFICER. [4576.]-BLACK BRASSWORK OF MICROSCOPE."J. Haines" may black the brass work of his telescope with a mixture of lacquer and lamp-black. This is what I used when putting in two new tubes into a 3ft. achromatic that had been broken by a fall.-G. W. A. [4576.]-BLACK BRASSWORK.-The inside tubes of microscopes are blackened with a mixture of lampblack and turpentine, applied with a soft brush. MEDICUS. [4576.]-BLACK BRASSWORK OF MICROSCOPE. -Vegetable black mixed with lacquer and thinned with spirits of wine is used for the insides of microscopes and telescopes by all opticians.-R. N. [4580.]-MANGANESE BATTERY. - Having never compared the power of the two batteries, I cannot satisfactorily answer "Northumberland Subscriber."A. J. JARMAN. [4582.]-GOLD LEAF.-"Chemicus" should buy a book of gold leaf, when he will find that the paper is exceedingly smooth, and that it is rubbed with powder of red lead in order to prevent adhesion.-H. W. [4602.-MELTING GLUE.-" S. N. R." must steep his glue eight hours in clean water, then put it in the pot, boil it, and then it is ready for use.-A. STORMENT. [4602.]-MELTING GLUE.-If "S. N. R." will break up his glue in small pieces, put it in his glue-pot with a little more water than will cover the glue, then put it over the fire, let it boil until the glue is melted, he will know if thin enough by the brush working light and free on the wood. Add a little water each time he melts it.J. G. [4602.]-MELTING GLUE.-The proper way to melt glue is to put cold water sufficient to cover it and when softened boil in the glue-pot; of course if it is kept melted long it will want more water added to it, on account ofevaporation.-R. N. [4602.]-MELTING GLUE.-Common glue may be frequently caught at once. No ground-bait is required. [4604.]-PICRIC ACID.-TO" S. H. B."-Picric acid is [4604.]-PICRIC ACID.-Picric acid is a nitro-substi- [4607.)-ORGAN BUILDING.-Stop diapason pipes [4609.]-AIR-CANE.-The drawing on p. 490 does not barrel; C, bullet; D, air way; E E, socket of striking [4612.]-PORTABLE MILL. In reply to Errac," I have a model of a portable windmill or engine for pumping with any description of pumps, or the same might be used for any other purpose, such as sawing, ploughing, grinding of corn, cutting chaff, or for any purpose where motive power is necessary.-JOHN JAMES. [4612.]-PORTABLE MILL.-I beg to inform "Derf Errac" that I never heard of or saw a portable windmill, except in a toy-shop. Mr. Vallance's plan is that of sailing ships, and must have required almost a harricane to drive seven ploughs. Windmills for draining were formerly much in use, but they have long since been superseded by steam power, as more economical and efficient. Gwynne's centrifugal pumps are much used now, but they frequently blow, and require filling up with water for a fresh start.-HENRY W. REVELEY. [4615.] SEWING-MACHINE ATTACHMENTS. "J. F. R.'s" machine being a shuttle machine does not show the sort of hem-folder he wants, except that it will most likely be left-handed. Something depends on the material he wants it for, and the size of the hem. I hope the replies to "J. F. R." will throw light on this subject for my sake as well as his.-AQUILLES. [4616.]-PROBLEM.-I am sorry that time will not allow me to work out the problem proposed by "Amicus "fully; but I will make all clear for him to do so. He must not be afraid of large complicated numbers and expressions. The question is solved more easily by trigonometry, yet as it is taken from "Newth's First Book," I imagine the algebraical solution to be what" Amicus" requires. Thus: -Let the diagonal C B of the С Е the parallelogram A B C D represent in magnitude and direction the resultant of two forces A C, CD, acting upon a point C at an angle of 135. Let A C C D. Let CB 100lb. It is required to resolve C B into its comPELLING 1 ponents. From B draw BE at right angles to C D meet I, br ais reser llar, bar ht jour Fa for renew and tare d. Bes to star of the rainLCANITE-3 polish bas alect make ther first a and od T en-ste sød & a speed, se and oil to f ed, and ches etting op s rcular lett Rud forw ashes are repir 4 amps, arte Such & & ing the latter in E. Because A C B 135, ABD = = By Euc. 1, 47, B C2 C E2 + B E23, P.S.-I do not think our friend will ever get such a [4618.]-MANAGEMENT OF BEES.-I agree with [4618.] BEE MANAGEMENT.-In answer to Thos. Poulton, there are several ways of feeding bees, but I believe the best feeder is the simples t, viz., a round zinc pan, as per sketch. A, zinc pan; B, honey, or sugar and water; C, floating board, perforated with numerous holes; D, entrance for bees; E, top of hive; F, super or working hive. There is a piece of wood, which fits into it and floats on the sugar and water, perforated with numerous small holes through which the bees insert their proboscis, and get nutriment without getting their feet, legs, or wings sticky. The feeder is placed on the top of the hive,and the bees ascend through the centre. Of course this is used with the humane or depriving system, other than which no amateur or any other bee-keeper should use. With this hive, which is as inexpensive as any,and which any youth with a little ingenuity can construct for himself, the little bees will produce more honey, and afford a constant and highly interesting study, for any time the bees could be seen at work through the glass doors. As far as expense goes bees can be kept in an old wooden barrel, providing it is clean, and put in proper position, &c. The simple square box hive, with two or three working supers, is a very good one, and gives very little trouble to the bee-master, and a strong healthy swarm will work three supers during the honey season. Should my brother readers require any further information on bees and beekeeping I shall be glad to aid them in every way I can if they will ask through your columns. FRANK. two thicknesses. == acid in a benker or bottle and cuts the gold into small see G. E. Davis's letter in this number. [4622.]-NITRATE OF SILVER.-"Photo" must precipitate all the silver out of his solution by the aid of hydrochloric acid. After standing a day or so, pour the water off, and get a clay crucible and mix the white precipitate (from solution) with charcoal and carbonate of potash, and place the crucible in a well-urged fire. You will obtain a pellet of silver, which must be dissolved in nitric acid and solution crystallized in a water bath.-OMEGA. [4624.]—“YOUNG JOBBER." The selection of a pendulum spring for a watch is regulated according to circumstances, namely-a verge watch requires one kind, a lever watch another kind, the duplex different again, and the horizontal again differing from the rest. Presuming that he requires a pendulum-spring for the lever watch, proceed as follows:-Select, or make, a pendulum spring to suit the size required, that is, that the spring is such diameter that the outer coil lies nicely between the curb-pins and free of the stud when the eye of the spring is exactly central with the potence hole. Let the spring contain about twelve to fourteen turns there is no recognized rule,to determine the length of wire or number of turns chosen by springers. All they have to avoid, concerning this part of the matter, is that the turns are not too close to each other, nor too open. A good kind of spring will have its turns the distance apart of four times the thickness of the wire of which it is made; the length of which will very much depend upon the size of the watch. In all probability the average length may be 5in. to 6in. Next find by counting the train of wheels-or by the old spring how many vibrations per minute-or half minute-the balance must perform, then secure the spring to the pendulum collet, attach it to the balance, hold the outer end of spring firmly by the tweezers, and while the lower pivot of balance rests slightly on a piece of glass cause the balance to have rapid motion by striking one of its arms, that motion may continue for 90 or 100 seconds, during which time count how many vibrations the balance performs in the time required, say half a minute. Thus the springer is guided in the selection of a pendulum spring.-SECONDS PRACTICAL WATCH MAKER. [4625.]-FLUORINE.-This element must certainly be reckoned as one among the normal constituents of the human body, though it only exists therein in a very small quantity. It is alway found in the teeth, more especially in the enamel, as well as in bones, particularly fossil ones. It also exists in minute quantity in most animal and vegetable products, in water, both salt and fresh, and in most rocks. There is, consequently, no difficulty in seeing how a supply of this element is sustained in the human body.-TEINITROPHENIC. [See also G. E. Davis's letter.] [4627.]-LEATHER DISCOLORATION.-"G. A. G." by the iron press. All iron liquors or sulphate of iron [4628.]-INTENSITY COIL.-In answer to " W. J. P.," I have made a coil from instructions given by "Dyer," and except that I have made mine only half the size "Dyer" gives, in every other respect I kept to his instructions, and had not the least difficulty whatever. When I connect the coil with two point-cells of Daniell's battery, the shock is so strong that none of my friends dare take hold of the handles.-J. D. [4629.]-MANGANESE BATTERIES.-I regret that your last issue, in which my name occurs, until now. I have, from other business, overlooked two queries in I have to state that my battery is simply the Leclauche, but without the accumulation.-W. H. STONE. [4618.]-MANAGEMENT OF BEES.-Feeding-bottles for bees are on the principle of the fountain for bird cages. They are readily made. Get a wide-mouthed glass bottle-a pickle-bottle, I usually have-nearly fill with Det of pleves syrup, have a piece of canvas and tie on the mouth as if ween daw you were tying down preserves, only don't have the cloth hole in the top, on this place a bit of perforated zinc, The hive is supposed to have a large holes about the size of the head of a pin. Carefully turn the bottle of syrup upside down on this zinc. No more syrup will leave the bottle than what the bees will rindas readily take up. See J. W. Pagden's pamphlet on bees, To make syrup I buy West India sugar, 4d. per lb., to every pound I add half a pint of water, boil for a few haf, minutes, say, five minutes, when cooling stir in a pinch of salt and a few drops of rum. On the 11th July, I had a swarm too late in my district to do any good. I hived it into a box 12in. square, 9in. deep, commenced feeding, each night giving a bottle of syrup, about a pound and a half, and on the 27th of July the box was full of beauti-point out to him that the said point will be found behind ful comb, having used 12lb. of sugar. In feeding, mind and don't spill any of the syrup, and be sure to cover the bottle, so that no bees can get to it, or you will have much fighting and so loose your stock.-J. [4632.]-WEIGHT OF BALL.-Ralph Williams in this query makes it appear that my former answer is characterized by two errors. But I am pleased to say that I am not accountable for either of the (apparent) errors. I think that" R. W." himself is accountable for the first one, and the printer for the other. In the first place "R. W." points out that he thinks I have missed a point (I presume he means a decimal point). If so I beg to the figure 7 in my former answer, and not before it, as he places it, which makes all the difference-7-854 being made to stand as 7854. In the second place the printer has misplaced a decimal point in connection with the weight of wire, 5, or half a pound, being made to appear when he knew that the weight of the wire was half-aas 5lb. I thought "R. W." would discover the error pound. He will see that dividing by five and dividing by point five, give different results. Perhaps a little explanation will assist "R. W." in comprehending the rule (which I hope is not too simple). Of its correctness I can entertain no doubt after twenty years' almost daily experience. The rule to obtain the weight of round bar iron is as follows: Multiply the square of diameter by 2618, which is the weight in lbs. of a lineal foot of round iron, lin. diameter. In working out the weight of a foot of tin. round wire for my former answer, I found that it involved several places of decimals. Itherefore took the find that he gives the weight of 8ft. of fin. round iron as weight of a yard, which, coming so near to half a pound, made the process very simple. On referring to Ponn Í 49; Spon gives 51. I take the mean and say 5, which is sufficiently approximate for all practical purposes. Of course I had to multiply the weight of a foot by three to obtain the weight per yard. Or else (which was more simple) multiply by the weight of a yard of round iron lin. diameter, which is 7.854. I did not attempt to split hairs, as I inferred from R. W.'s" first query that he only wanted a rule whereby he could obtain the weight of round iron in the shape of round balls and round wire, so I gave the weights in round numbers. I may now inform "R. W." that the 146 made use of to obtain the weight of a wrought iron ball is the weight of a wrought iron ball lin. diameter. So that the cube of any sized round ball multiplied thereby will give the weight in lbs. I think I have now said enough in explanation of the rules and the reasons for the rules, and think that if "R. W." will try again (bearing in mind these corrections) he will succeed to his own satisfaction. It is scarcely necessary for me to work the sum now. But I do so with pleasure, hoping thereby to satisfy R. W." Weight of ball 7in. diameter. 78 x 146 = 50078. Weight of a yard of fin. round wire 252 × 7·854 = For simplicity I take the weight as 5. There If "R.W." will invest 2s. in a little book published by Charles Fox, Paternoster row, viz., "Penn's Tables," showing the weight of round, square, and flat iron, brass, copper, I think he would be pleased with the same and find his weight too heavy for a cubic foot of cast iron? find it a cheap two shillings' worth. Does not J. Nash Most authors give it as 450 lb. This will account for the 3 lb. difference between my weight and his of a 7in. ball.-FERRUM. [4634.] - ELECTRIC CLOCK. — TO “ELECTROMAGNET."-I may add that the clock is equally unoriginal, being a Swiss patent, exhibited in the last Paris Exhibition. I heard of it from my friend Dr. Grabham, of Earlswood, and procured one through his instrumentality. The English patent has been bought by Mosely, of Covent Garden. The only points to which I wished to draw attention were the mode of the action.-W. H. STONE. making the battery and the remarkable permanence of [4635.]-CAKE COLOURS.-Procure a small slab and muller of glass, and grind the powders into a smooth stiff paste with equal parts of isinglass size, and thin gum water; compress into squares as closely as possible, and dry with a very gentle heat. Old crumbling cakecolours, may be powdered very finely in a biscuit-ware mortar, and sifted through fiue muslin, and ground up as above, omitting the gum water in the medium. the powders are rubbed up with honey (despumated) to the consistence of thick cream, they auswer admirably as moist colours.-SABLE. If [4640.] - SOUTH KENSINGTON EXAMINATION PAPERS.-If " J. B. H." sends direct to South Kensington for the examination papers, they will be sent to him by secretary, Science and Art Department. He will have to pay for them, 6d I think.-C. H. W. B. [4648.]-TWO COINS.-The upper one is a PAXS penny of William I., possibly one of the 12,000 or so found on the property of a Mr. Dunn, of Beaworth, in REX (William King), and on the reverse is "OCMUND Hampshire, in the year 1833. The obverse is PILLELM ON SUDE," Osmund being the moneyers name, and Cude the place of coinage, Southwark. The letters PAXS in the angles of the cross, by some, considered to be an abbreviation for "Pax sit," a not improbable expression of hope for peace in the troublous times of the Conqueror (v. Ruding). The lower coin is a sixpence of Philip and Mary, date 1554. Value depends on condition.-T. W. BOORD. [4650.]-FRENCH LANGUAGE.-I think "Ollendorff's Method" would suit "Patty" very well.-G. W. A. [4652.]-TONING BATH.-I have used the following for the last four or five years, and know of none superior for rich purple tones:-30grs. acetate of soda, 10oz. water, 5grs. carb. of soda. This to be mixed some hours before wanted, and chloride of gold sufficient to tone the prints in hand added just before required for use. The bath works quickly hot and slowly when cold. I always prefer it hot, and the solution may be used over and over again, ad libitum. I may also add that for the last three or four years I have always used nitrate of potash in my sensitizing bath in the proportion of 3 of silver to 1 of potash, and obtain richer tones and more glossy prints by so doing:-2oz. nitrate of silver, 1oz. nitrate of potash, 200z. water, neutralized by a little carb. of soda. I never have any "old" bath. I use it up until there is not sufficient to float my paper, and then add fresh. UNIT. [4653.]-SUNDIALS TO SHOW CLOCK TIME.Wishing still to leave this problem to your readers' ingenuity for a month, I will only give the querist of p. 574, at present, the information that should enable him to solve it. 1. Astronomical.-The "Meridian of mean time," or that line in the apparent heavens which contains the place of the sun's centre at every 12 o'clock, may be plotted by attending to the two columns, in any almanac, of equation of time and sun's declination. It has the form of a long italic 8, so leaning across the true meridian as to touch the northern tropic about 14 minutes (of an hour) west, and the southern about 1 minutes east thereof. This leaning slowly increases, and will for many centuries; but the inequality of the six centuries ago, when the 8 was last upright. The two loops is decreasing, having been at its maximum leaning is alternately to the right and left, for about 6,000 years each; but each loop is alternately largest for twice that period; and the southern has been largest ever since Adam's time, when they were last equal. The widest bulge of that loop is now somewhere about 15 of S. declination, and that of the smaller loop, 20 N. The crossing of the curve on itself is some minute west of the meridian, and about 10 N.; and its four crossings of the meridian are at some 9 and 10 N., at a point very near the northern tropic, and at one still nearer the southern. I expressly renounced the showing of true clock time for a few days of midsummer and midwinter, namely, when the sun's declination exceeds the last-named two points. I should add that the indications of all dials within half an hour of sunrise and sunset, will always be vitiated by refraction, and the scale should never extend to those hours. 2. Optical. The solar shadow of every object is bordered by a penumbra, whose angular width equals the sun's apparent diameter, and the theoretic shadow's boundary (as it would be cast by a star occupying the place of the sun's centre) is half-way between the edge of pure shadow and full light. But while the former of these is always perceptible, the latter never is so with accuracy. Therefore the shadow boundary to be used practically in dials must always be that of pure shadow, which is within, or less than, the theoretic shadow by half the sun's diameter at the time.-E. L. G. [4654.]-OCCULTATION OF SATURN.-"Hesperus" will find no difficulty in interpreting the Nautical Almanac account of this phenomenon if he will refer to page 164, where he will find that the horizontal parallax of the moon on September 30th is about 59. This is the maximum amount by which the moon's apparent place in the heavens may be shifted from her place as supposed to be viewed from the earth's centre. Further, her semi-diameter on September 30th is more than 16', so that even though Saturn were 75 (i.e. 59 + 16) from the moon, supposing both to be viewed from the earth's centre, he would be occulted as seen from some parts of the earth's surface. He is actually about 564 from the moon, southwards, at the time of conjunction; so that, as seen from stations having more than a certain northerly latitude, he will be occulted.R. A. PROCTOR. " [4654.]-OCCULTATION OF SATURN.-Without examining the Almanac, it seems pretty plain that Hesperus" must have overlooked the moon's parallax. The elements he quotes, are doubtless given for the earth's centre, not Greenwich; and apply to the place where the bodies will be vertical. The Almanac does not predict an occultation there, but at Greenwich, which is quite possible while their geocentric distance is as great as he states; the moon's horizontal parallax being greater, and Saturn now never much above our horizon.-E. L. G. [4655.]—MANGANESE BATTERIES.-TO "F. H. B." -I protect my connections from corrosion with a small plate of platinum foil under the copper. I understand, however, it is possible to prevent corrosion by making the carbon very long, so as to project some inches from the solution, and painting a thick band of shellac varnish round the projecting part between the fluid and the binding screw.-W. H. STONE. [4664.]-PRESSURE OF WATER.-The pressure per square inch on the bottom is the same in each case. The pressure of a fluid on the bottom of its containing vessel depends on the depth of the fluid and not on the form of the vessel. "Holbeck" may demonstrate this for himself in the following manner:-Take a plane tube A, and to the bottom fit a water-tight valve, V. This may be pressed up by means of a lever, a b, as shown in the sketch. Fbeing the fulcrum and W the weight. Water must now be carefully poured in till the valve just begins to open and the height of the column of water noted. Now perform the same experiment with a tube of the form shown in the sketch B, the bottom of which has the same area as that of A, and let the valve be pressed upwards by the same, or a similar lever and weight; on pouring water in, the valve will just begin to open when the height of the column is the same as it was in A.-EXHIBITIONER AT ROYAL COLLEGE OF SCIENCE. [4664.]-PRESSURE OF WATER.-No difference, of course. -E. L G. 46 It is the most elementary fact in hydrostatics. [4664.]-PRESSURE OF WATER.-In reply to Holbeck," the pressure per square inch at the bottom of each pipe is exactly the same, namely, about 5:29 lbs. -THOMAS J. O'CONNOR. [4665.]-PROBLEM.-a. Call the regular length of journey minutes. The train proceeded regularly 60 minutes, then stopped for 30, and had to do the remainder, which would regularly have taken - - 60, at three-quarter speed which occupied (x-60)-The 3 whole took, we are told, x + 110 minutes. Hence 4 (A)90 + (x 60) =x+110. 3 proceeded 90 minutes right, and stopped for 30, it would have had to do what usually takes 90, at three-quarter 4 speed, requiring (x90) and these times, we are told, 3 Next, had the train would have made + 100. 4 Hence (B) 120 + 3 x-90) = x + 100. Rejecting the figures common, to both sides, equation (A) becomes (09 - x) =x+20; and 3 tion is correct, and sufficient alone, with none of a, to determine that the regular length of journey was five hours.-E. L. G. [4668.]-LATHE. TO "TOMETER."-You ought to be a pretty good judge of what you are able to do. A great deal more is required in lathe making than a mere knowledge of turning. As to price, the £100 and the £25 lathes are probably each worth about its price-plus profit. You want an amateur's lathe, that is, one fit for a gentleman's use, and seem to think that you can get it somehow at the price of one that an apprentice would be set to work at. Do not, pray, make a 4 lathe nothing less than 5. I should get the bed cast and planed and fitted on to standard, and fly-wheel and treadle fitted complete as a first start, and I reckon to get that well done will take £11 more or less for a 5in. You can add a leading screw at any time after all the rest is complete, and the bearings for screw may be cast on or screwed on afterwards as you please. And all the above work I should entrust to Wilkinson, and nobody else. You can get a 5in. lathe of Whitworth with sundry chucks for £90. One of Muir's for less than that, and one of Smith, Beacock, Tannett, for a little more than half Whitworth's price.-J. K. P. [4668.]-THE LATHE.-Perhaps "J. K. P." will pardon me for answering a question addressed to him. I do not think £25 at all an adequate price for a lathe such as "Tometer" describes. If he wants a good lathe and has not the money handy, he might borrow it, and, as he says his time is his own, he could easily earn the interest of the money advanced, and so gradually pay off the debt.-G. W. A. [4672.]—KITE.-The kite would certainly not act as "W. J." describes, for suppose it to be suspended in the air as he proposes, and to be inclined at an angle, say of 45, which would be about the proper inclination; then the wind pressing on the inclined kite would act in two ways, it would tend to drive it along horizontllay and it would also tend to drive it up perpendicularly, and as these two forces would be equal, and supposing there be nothing to oppose or diminish either of them, the utmost the apparatus could do would be to move in the direction of their resultant, or in other words it would move up from the earth in the direction of the wind at about an angle of 45. But seeing that the weight of the kite and its appendages would diminish the force of its upward tendency, and that no opposition whatever would be offered to its horizontal motion, the practical result would be, that though it might possibly rise up into the air, it would, at the same time, move along with the wind at a much more rapid rate. In order that any apparatus may beat up to windward, it is necessary that it should have something to hold on to, in order to prevent it drifting to leeward. A boat beats up into the wind because its length gives it a firm grip on the water, and a kite will beat up to windward (as indeed all kites do when they rise up from the earth) provided it is held by a string to prevent it going with the wind. A kite could no more work up into the wind without being held by a string, or some equivalent contrivance, than a lever could be used without a fulcrum. The ap paratus " W. J." describes would drift hopelessly along with the wind.-W. [4676.]-NITRATE OF SILVER.-Refer to replies to query 4622 in last number.-T. W. BOORD. [4676.]-NITRATE OF SILVER.-The sediment from "Paddy's," salted "slops" is chloride of silver. His best plan is to collect the sediment in a large bottle, and when full, sell it to a chemist, together with all his old filter and draining passers, or get the chemist to convert them for him into nitrate.-UNIT. [4678.]-BOURNE ON THE STEAM ENGINE.In reply to Thomas Watson no better work than "Bourne" is at present published on the steam engine. "Main and Brown on the Steam Engine" is also a very engine.-THOMAS J. O'CONNOR. good work, but it treats principally on the marine [4689.]-PEDOMETERS.-The motion of the body in walking causes the vibration of a short weighted arm or pendulum which acts upon a small toothed wheel, geared into another connected with the index.-UNIT. [4691.]-POWER OF ENGINE.-According to the rule to which "R. W." refers, the power of his engine at 30lb. pressure would be horse power, thus, 2 x 2 = 4 ÷ 12 = 4 12 therefore three times the given pressure, or 90lb. per sq. in. horse power. With respect to the thickness of boiler would be necessary to enable the engine to work up to 1 plate, I must refer "R.W." to some practical boiler maker, whose advice will be safer than mine, for 90lb, is an unusually high pressure. If possible, it would be far better to use an engine with a 3in. cylinder, since then, the pressure need not be more than 40lb., the expense of boiler being, of course, proportionately reduced.-VER TUMNUS. [4693.]-BICHROMATE BATTERY.-The plates are usually about gin. or in. between the faces. The resistance of the solution is so small that I think very little powder would be lost, and greater constancy be obtained, if they were lin. apart. The plan for connectbattery in my papers) is the best possible-viz., electroing (given under the heads of "Carbons" and this typing the top of the plate and soldering.-SIGMA. [4701.]-CLEANING COINS.-Caustic ammonia will clean silver coins. Much more harm than good is likely to result from attempting to clean coins of any value.T. W. Boord. [4706.]-PHOTOGRAPHY.-"In a Fix" has overdosed his washings with salt. A very small quantity of salt is sufficient; too much undoes it all. "In a Fix" had better put all his future washings into another mug and try to precipitate the silver by adding a little of the over-salted Their half sum is washings to it instead of salt, and so gradually use it up. (x-75) = x; so that x = 390. UNIT. [4709.]-PROCTOR'S TELESCOPE STAND.-The dimensions of the stand figured at p. 17 of my "Half hours with the Telescope," can be gathered from the fact that the telescope was of the size and "Turton"-that is, 4in. in aperture and in ord length. I do not recommend the stand as a figured. The toothed wheel and quad.aut expensive; and, again, the legged part of the ma should be higher in proportion. The rest quadrant should be replaced by a semir teeth; a cord carried along the circumfere semicircle and making a turn round the ad R the endless screw in my figure, serving thedo tinuous motion in altitude. In like EM round the circle c, with a turn round the the crown-wheel, would give the continenta azimuth. The figure is really a picture modifications, of a telescope I used it Marlborough School. The crown wheel from a part of the appurtenances of a wise I also filed and set the endless screw, and of work I made of it, more by token toon wheel working in the crown-wheel was ma breaking a knitting needle into four equal tying these () parallel to each other roun a rod. The instrument, when thus complete singular combination of the expensive and the arrangement worked well all the same; and place; but the knitting needle and the en of having the two handles, which give the sha azimuth motions, always in the same fixed nient position, was such as to make one t instrument was an alt-azimuth.-R. A. PROVE [4713.]-BEES.]-They will pass in and on such a hole as you describe, provided you c entrance of their hive with it in such a mata prevent their escape into the room where th kept. Move them at night, and in the morn will take the bearings of their new locality befon za mencing their labours, so as to be able to find the back again. For feeding in winter, use a syrup EM of white loaf-sugar, boiled down with water, sbulti pound to a pint.-T. W. BOORD. [4721.]-FOSSILS.-"H. U." ought most certainly te find some fossils in the locality between Cromer and Hunstanton. The Tertiary system is very fully dere loped in that neighbourhood, and amidst the Crag of the Pliocene group he may chance to come upea the remains of small mammalia analogous to the mouse, also teeth and bones of placoid fishes, and corals, and -hells of innumerable species; marine plants are likewise to be found. The strata consist of marine and lacustrine deposits of shelly beds of sand, clay, and yellow leam, and flinty shingle, generally resting on the chalk system. H. U." should wander into any gravel pits or quarries, &c., and closely scrutinize every rock near which he comes; he should also provide himself with a hammer for the purpose of detaching specimens. The chalk or Cretaceous system lies immediately below the Tertiary and is rich in shells.-ARTHUR UNDERRILL. QUERIES. [4725.]-SHORT-SIGHT.-Could any of your scientific readers give me a little advice under the following ar cumstances? I am very short sighted, so much so, the I am unable to recognize a person ten yards distant, which is very inconvenient for my daily occupation. I am 21 years of age, and my sight has gradually got shorter since 14. Is it prudent to wear spectacles (I have a g horror of them), I have heard they strain the eyes sad otherwise prove injurious.-MOSES. [4726.] - -HOROLOGICAL.-TO "NOBODY."-Thanks to "Nobody" and others for their kind replies to queries, No. 4,128. I never had the pleasure of read such a welcome communication before him I found it practical to the letter. Will that gent "Nobody's on watch jewelling; and allow me to man kindly inform me how to turn in a new verge, s also how to fit a balance wheel to a verge watch, naming tools to be used in the same, and oblige?-COMPENSATED BALANCE. [4727.]-TO "OMEGA."-I am very much pleased Slater's iron cell. Would he kindly inform me where I with the results given by "Omega" in his paper on can obtain nitrous acid at 4d. per lb., and also nitrate of soda at 14d. lb.? I should very much like to know the results obtained with his 36 cells.-A. J. JARNAN. [4728.]-TO "SIGMA."-I am glad to hear that Sigma" is going to compile his present papers s electricity. book. Undoubtedly it will be about the best wÀ S The iron that contained 65 per would like "Sigma carbon was a piece of common cast-iron gas-pipe to inform me how zine can sodium in a solution of sodium chlori e, as beas does; while in one of his former papers he say that zinc cannot replace sodium in a solution of m chloride, and I think so too.-A. J. JARMAN, [4729.] TO MR. PROCTOR. - Mr. Proctor 78 a Arietis is visible in a 3in. Will he say what is the angular distance and magnitude of the compon sts? Does Mr. Wray use a cement, liquid or solid, as a cocave lens in his glasses ?-AQUE SOLIS. [4730.]-NAIL MAKING MACHINE.-Can any corre spondent inform me what would be the cost of a machine to make cut nails, and how many different sizes one ca NAIL MAKER. make, and also what power is required to work one [4731.]-TO" SIGMA".-I shall esteem it a very favour if "Sigma" will inform me whether soaking portion of a carbon plate with paraffine to preve absorption of liquid, as suggested by him some tis since, would not have an injurious effect upon its L ductivity.-DEDALUS. [4782.]-GAS-TAR.-Would "Sigma," or any reader kindly inform me how gas tar is prepared, so that its alcoholic solution would form an emulsion with water.DOMINO. [4733.]-BRONCHITIS.-Can any of your readers inform me of a cure for bronchitis ? I am much troubled with it, especially when I walk a distance in a hurry, the tubes get full of mucous, and expectorati on is the only relief; at times the mucous is streaked with blood. 1 bathe the throat and chest with cold water frequently, and have found it a great benefit, but the disease or trouble is never away, and is annoying.-OMEGA. [4784.] REMOVING WRINKLES FROM PRINTS.Will a brother subscriber inform me how I can remove wrinkles out of a coloured print? The print is fastened to the back of the frame with gum or some other adhesive substance, but in places it is drawn from the back and rose up in wrinkles.-WINNER. [4785.] PEARL OYSTER-SHELLS.-Can any one tell me where the above are to be purchased and the price? -THOS. FLETCHER. [4736.] BALANCE IN VERGE WATCHES.-Will any of our watchmaking brothers enlighten one desirous of gaining knowledge as to the best way of uprighting the balance in verge watches when the cock and potence holes are worn and want refilling, or have been refilled, and left with balance leaning on one side? What I want is the best and easiest method of setting out the holes so that they shall be perfectly perpendicular, as I find frequently that watches which have been so repaired fail in this essential point.-CHEEK-ACHE. [4787] BLOWPIPE.-I wish for some information upon the practical use of the blowpipe. I possess one 10in. in length of brass, and can manage to braze small articles such as watch hands, &c., but when I attempt to solder new joint or pendant on watch case with silver solder it results in a miserable failure. I use a common tallow caudle, or in place of which I use a small benzine lamp filled with benzoline. Then I place a little powdered borax on the joint, or whatever it may be, with the silver solder on the top, then placing the article in my left hand I direct the blowpipe and flame with my right hand upon the work, and blow till the borax is melted and the silver also, which has been laid on in a strip, which runs into a small round globule glittering and dancing beneath the heat of the flame. This is all that I can attain. The fault appears to be that I cannot obtain sufficient heat in the article to be brazed to enable it to take the solder (but I may be wrong), although I may blow till my cheeks ache and my eyes start. Is the fault in the blowpipe, the candle, or lamp, or want of oxygen in the breath, or where is it? I know that such work is done daily, and hope to receive instruction through your columns.-CHEEK-ACHE. [4738.] GEOLOGICAL.-There is a matter which has puzzled me much, viz., the "cause" of the intervening strata, or the sandstone rocks, which is found between the different coal beds. In other words, if the vegetation of the coal bed periods has been caused by the heat of the sua and seasons, what has been the "cause" of the sandstone periods?-VERITAS. [4739.]-COLOURING SIZE.-As no correspondent has answered many query, 4317, page 480, can any one tell me what to put into the size to make it a very pale blue, as I find by putting indigo into the size it makes it a green?-JOHN BURY. [4748.] ELECTRO-MAGNETIC BATTERY.-Will the amount of steam contained then expand and do the same amount of work, as an engine without the some kind reader inform me how to construct the above so as to produce a strong magnetic current? any valuable hints will be acceptable.-BERIRO. [4749.]-CARBOLINE.-Would "C. D. C." be kind enough to state where I can obtain carboline, and at what price per gallon ?-A. J. JARMAN. [4750.]-SOFTENING AND PURIFYING WATER.I should be glad if some correspondent could tell me where I could get a description of "Clark's patent for softening and purifying water," as mentioned by Dr. Frankland in his report to the Registrar-General for the month of July, and referred to in your number for August 19th, p. 182.-J. C. [4751.]-TAPS AND DIES.-In the ENGLISH MECHANIC for August 5, W. Reed asks (4434) "if he can make left-handed taps and dies from a set of taps and dies for right-handed work," and on the 19th "Semper Paratus" replies that he can; "he has only to work them the other way or backwards." Will Semper Paratus" please say if he has succeeded in producing serviceable tools by this means alone -T. W. BOORD. [4752.]-DIFFERENTIAL CALCULUS.-Will some one show me how to do this sum? It is in " Woolhouse's Differential Calculus," p. 27:— If u = (a2 + x2) 23 3 2 x+ √α2 + x3 F. P. [4753.]-GERANIUM PROPAGATION-Will a brother reader give me a few hints how to slip these plants, and whether or not I am to put anything to the bottoms of the slips?-J. E. CLAY. [4754.]-DRESSING SKINS.-Will any reader kindly inform me how I can dress into mats such skins as sheep, deer, and dog?-TAWER. [4755.]-CONICAL WINDING DRUMS.-Will some brother reader kindly give some particulars respecting the construction and working of conical or spiral drums as applied at collieries for drawing coals, and state what conditions are to be observed in order to ensure their safe working ?-W. M. [4756.]-CONSTRUCTING MAGIC-LANTERNS.-Can any of your numerous readers inform me how to construct a magic lautern; where the lenses may be procured, the prices of such, or how to grind them; and material required for such purposes ?-A. STORMENT. [4757.]-GAS PRESSURE GAUGE.-Will any one give me an explanation of a gas pressure gauge?-ALEX. OGILVIE. B cylinder A?I think it will, because of the piston allowing its full area to receive the pressure; but would like to know if there are any rules to determine the force of my argument.-ONE. [4766.]-STAUNCHING TIMBER JOINTS.-I would feel much obliged by any reader informing me as to the best material for staunching the joints of a canoe (timber-built, of course). Is marine glue used for the purpose, and if so, how prepared for use ?-ANTARES. [4767.]-MODEL PADDLE-STEAMER.-I am making a model steamer (paddle), about 7ft. long, and wish to fit air compartments to prevent immersion; will some kind reader inform me how to do it, and what to make them of?-T. K. [4768.]-POLISHING PLASTER OF PARIS.-Would you or some of your numerous readers inform me how to polish plaster of Paris ?-A TWO YEARS' SUBSCRIBER. [4769.]-CIVIL SERVICE EXAMINATIONS.-Can any reader give me information respecting the alteration in the Civil Service? Why the examination is done away with, and what course of study it involves? I shall feel much obliged for any information on the subject. J. M. C. [4770.]-FIXING PRINTS ON CARDBOARD.--I have a quantity of prints I wish to aflix on to cardboard, and should be obliged if any of your readers would favour me with a recipe for a paste or cement for fixing them and the best method of doing so.-T. E. [4771.]-FLUX FOR BRASS, GUN-METAL, &c.-Will some kind reader inform me what flux is used for brass, gun-metal, &c., and how? In running the metal into a mould I find it leaves a crust hanging from the crucible, and however smooth the mould may be it turns spongy, and not solid, therefore very often of no use. The flux, I think, clears it in a great measure.-LILLIPUTIAN. [4772.]-HERB BEER.-Will some reader of the ENGLISH MECHANIC give me a receipt for making cheap herb beer?-ANXIOUS. [4778.]-CAUSE OF THE EARTH'S REVOLUTION. Can you give me any idea what causes our earth to revolve? I can understand it being set in motion, but why does it go on, as far as we can judge, at the same rate for at least thousands of years? Call me, if you like [4758]-FRESHWATER FISH AND FISHING.Being an ardent follower of "Old Izaak" and "the gentle craft," I always read with interest "A. T.'s" replies-A MOKE. to questions. Can he inform me of any places near London where good fishing can be had on payment of a small fee; or where permission can be obtained on writing for the same? The great drawback we workers town have is the difficulty of finding spots near at hand where, in our few hours stolen from toil, we can seek recreation at once harmless, healthy, and amusing. -PISCATOR. [4759].-POLISHING WALKING-STICKS, ETC.-Wil! any of our numerous contributors kindly tell an amateur the best polish to use for walking-sticks, umbrella-sticks, &c?-WHITETHORN. [4740.]-CONTACT BREAKERS.-Will "Sigma," or answer me.-GEORGE. [4743.] HEM-STITCHING MACHINE.-Can any [4745.]-STARCH.-What substance can be used [4746.]-SCREW CUTTING.I should be very glad if our kind correspondent "J. K. P." would give me some information on the screw-cutting lathe. I have a four-foot lathe with back gear and slide rest, the bed flanged same as ordinary screw-cutting lathes, and saddle to fit. What I want to know is what form of nut he would advise me to use? Being only an amateur, I do not want a complicated affair. I have had a screw cut for the lathe, but no nut for it. The pitch is fin. square thread. Would he advise me to have a split nut or solid [4760.]-EXPANSION OF STEAM.-1. In Spon's "Dictionary of Engineering" under this head, page 428 (article "Boiler"), it is stated that "the dual logarithm of a given number can be calculated without the use of tables in a few minutes." As my table of hyperbolic logarithms goes only to the number of ten, I should be glad, having to calculate the mean pressure of steam corresponding to a ratio of expansion of 1 to 17-47, to have the rule as to dual logarithms explained, so as to be able to employ it (?) for any ratio of expansion. 2. Not being up in logarithms, would any kind brother reader give me a table of hyperbolic logarithms of numbers from ten upwards to twenty, and also explain how the hyperbolic logarithm of a number and frac tion (or decimal fraction) of a number between units and fractions of units in table is determined. Example: Let the number be 4.70. The next lower number in table is 4:50 (44), for which the hyperbolic logarithm 1:5040774 stands, and the next higher, 475 (4) for which the hyperbolic logarithm 1:5581446. I want to know how I am to find the hyperbolic logarithm of No. 470. 3. What is the rule for finding the end or ultimate pressure of steam (not the mean) for any given degree of expansion? Does the pressure decrease exactly in proportion to the increase of volume ?-A. W. E. [4761.]-SLIDING RULE.-I wish to know how the scales, or rather the divisions, are laid down, that is, set out on the sliding rule, for working proportions, areas, divisions, &c. Information will greatly oblige. -ROBERT BRIDGART. [4762.]-DISPLACEMENT OF SHIPS.-Would Mr. W. Felton give a sketch of his model, and how it is divided, for computing the displacement of ships? As models are generally made of wood, will the rule hold good for iron ships ?-G. B. D. [4774.]—THE AILANTHUS.-Will some of your correspondents kindly give me some particulars of the Ailanthus silkworm? I wish to breed a few. 1. When does the egg hatch? 2. How long before the larva becomes a chrysalis? 3. When does a chrysalis hatch ? 4. Where is the plant to be procured upon which it feeds? 5. Where can I procure some eggs? I have seen the names of other silkworms but do not know where to look for of them also.-A CONSTANT READER. them, but shall be glad to have particulars of one or two [4775.]-LUMPS ON HORSES.-Will any of your renders kindly inform what they consider the best cure for small lumps on horses, commonly known as "heat weals," and what to apply when they break under the collar ?—A GROOM. [4776.]-LATHE.-Your correspondent T. W. Boord, gives the numbers on the division plates of lathes by different makers. It would interest many to know the size and pitch of the screws on the respective mandrels, and whether the same gauge is adapted for " ornamental lathes as for those for general use; also the diameter of the dividing wheels and pulleys of each lathe. I presume the lathes referred to are 5in. centre.-AMATEUR TURNER. [4777.)-LINK MOTION.-I am surprised to see "R. W. B's" question (4581), after the very clear and intelligible papers by Mr. Baskerville on the subject. May I ask Mr. Baskerville to explain a sentence in the last paragraph but one in his last letter about the stationary link as applied to the locomotive? He says it requires "a length altogether out of the question in a screw engine or a locomotive." To what extent the word properly applies I know not, but there are a large number of engines running on the London and NorthWestern, and London, Tilbury, and Southend Railways with this motion.-G. W. A. [4778.]-DENTISTS' CEMENT.-Can some one in form me how the cement that dentists use in fixing the teeth in the metal is made?-X. L. [4779.]-HOLTZ'S ELECTRICAL MACHINE.-Will "Sigma," or any other correspondent give a description of Holtz's electrical machine, or state in what work English or French, the same may be obtained? -A REVENUE OFFICER. [4780.]-TEMPERING STEEL NEEDLE WIRE.— Will any one inform a brother reader how to harden and temper fine steel needle wire in 30 or 40in. lengths? [4763.]-SOLDERING BRITANNIA METAL.-Now nut with bevil wheels to work with handle at the by " Sergius," cannot understand the composition of bell-AN OLD SUBSCRIBER. "J. B-h," having examined the recipe as described front? I see that he has sent some useful informa- metal, thinks it may do very well for iron and brass, but tion on the lathe, which encourages me to ask him to do me and my fellow readers a great is afraid to use it for Britannia metal. The latter being favour. -JOSEPH MOSELEY. so soft, whilst bell metal so hard. "Sergius's" reply would oblige.-J. B―h. [4747.)-GLASS BURNING.-I am afraid Mr. Ashton will think me very dense, but I venture to ask him for a diagram of his brick furnace, described at page 476, also for replies to the following questions:-What is the medium used for painting on the colours? Is it necessary to submit the painted glass to the action of heat after laying in each separate shade, e. g, as in flesh tints. draperies, &c.? The painted glass is directed to be placed between layers of quicklime,--will not the lime mingle with the colour during fusion, and injure its evenness and transparency, what kind of fuel is most suitable? Will the red protoxide of copper yield a good ruby colour, and oxide of manganese a good amethyst ? -SABLE. [4764.]-BRONZING COPPER URNS.---Can any of your many readers inform me of a simple way of bronzing urns for hot water, chiefly used on the tea-table, value about £5 each, colour very dark copper colour.-J. B-h. 99 [4781.]-SUSTAINING BATTERY.-Could "Sigma or any other electrical reader give me a description of the battery used for working Tyer's railway block signals?? It has been described to me as a box containing eighteen stoneware cells, and at the bottom of each cell there is something very bright like mercury, this is all the infor mation I could gain on the subject. I am very anxious to learn what this battery is, and how long it will remain in action.-CODE. [4782.]-TOMATO SAUCE.-Can any reader give me and working through the bottom of the steam cylinder in a simple recipe for making the above sauce?-BON [4765.]-PISTON AND PRESSURE.-A represents a cast iron cylinder fastened to the piston-road as shown, the same manner as an ordinary horizontal engine. I will suppose the engine to be an expansive one. Now in my plan the piston, having its full surface exposed to the steam, must, when the ports are open, have the same pressure on it as though the cylinder A were omitted. So far all right, but when it (the steam) is cut off, will VIVANT. [4783.]-CONVEYANCE OF WATER.-How much power can be utilized from a supply of water conveyed 150 yards in 1in. piping with a fall of 12ft.? What is the best means of guning that object,-combining the attainment of the greatest percentage of power with sim |