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> "very-day electricity indeed, and hence their value * I it niiiu' preventors, not attractors. Yon can disS^jo, silently and withont shock, the largest electrical a ry, by simply holding one pole while you present i"»-r-p needle toward the other. In this way there is Loubt every right lightning ondnctor helps iu a nra. to discharge tho cloud silently, and prevents L«as that would, without it, have occurred. But in a xeeasivc tension of storm electricity this purpose ~> tetter served by delicate needle points than by

accidental raggedness of any metal termination. ry experimenter kuows this is the case even with an trical machine iu good order. Doubtless there is a ^ rencei Iwtween the action of Messrs. Newall's

i tilul "attractors" and a broken bar end in tun«r, but not in a storm. If anything can be Baid to zvet lightning it is the poiutedness of the whole liing or rising ground. Spikes make no difference, cxiobs as big a* any dome; and nothing can bo more u_x-d than carrying ont conductors an inch above or r*rtd what they are to protect. (The poor Duke of 'Is. is spitted on the top of his column I) . insulation is eqnally preposterous, as your second wercr perceives. It is abundantly proved the elec-ix\ passage will never turn aside from tho line of t <-oiidnction.

.. For his "taken deep enough into the ground," „tl simply, "taken to the next metallic mass that ^ metal comranuication with the gronnd." As every nlrrn English building has metal water-pipes from 3 ground up "to the metal gutters," it is so far ktolntely protected already. Accordingly, I defy you <-itoaeaseof damage by lightning in all England,

tin- century, outside a building and below the level its gutters. They are either on the outside, above I gutters, or inside, by descending a chimney. No mdnctsrs to the ground then are ever wanted,—you Fvve them already—bnt simply from chimney tops, or t-her "attractors," to the nearest gutters. Whatever icital then you see spent nnder colour of lightning pro;«.*tion, loiter than the highest gutter level, is merely >bbud iu for "percentage" by quacks, patentees, rehitects, et hoc genu* omne, that the mighty wisdom V Mr. John Bull creates as his ornaments and oracles, is percentages. I saw once a poor (not in benefice) •arson, whose school-house was being lightning connctored entirely comme il /nut—pointed attractors of

:':<■ f. finish,—the insulators that F. Bedford would asely imitate with " bottle-necks,"—and all. Being a ue day, as they carefelly brought the work downwards, efore connecting with the ground, it gave beautiful parka, of course to the astonishment of b^ reverence, lie M.A., whom Oxford had never informed of such a bins as electricity, and of course that showed beyond Luestion thut all is right, and we are in the hands of nen of true science. Could he or his builder have node sparks appear from the rods? What could be uoroc mvincing or satisfactory that what is here speut s well ."'lit? Now this could only be done, observe, vith finely sharpened "attractors" and good iusulaion. Hence you see what all this is wanted for.

G. But though conduction is needed only to the jntters, please observe it is needed from every point table to be struck. Cases innumerable have exploded ho old French error that one point—the highest—will »roteet the rest of an object. Ships with every mast jrotected have been struck on the end of a yard. All ire can say is that no case is known of lightning strikug a point within or behind the plane of three others, •r the line joining two others. This defines exactly, in the largest building or town, all the points liable to lightning stroke. They are just as fixed and ascertainabb* as the number and position of letter-boxes, or of barber's Bhops. On St. Paul's Cathedral there are four; on Westminster Abbey, seven; on Salisbury Cathedral, hix. To know precisely the points needing protection, all you have to do is to imagine a model of your building, aud that you have in your hand a circular plane, say, a tambourine, as largo as it would stand upon. Whatever point you could touch with the centre of this plane, without touching other points, is a poiut liablo to lightning stroke, and no otter point is liable. So at lea>t wo have a right to say, till some instance be adducible of a point not thus defined being struck. Protection from lightning, therefore, is just as simple and absolute as exclusion of rain from a building, and it is nttarly wanton and inexcusable that such a thing as injury to a public building by lightning, in a civilised country, should ever occur or have occurred in this generation. Nowhere but among percentageTM could it now occur, any more than destruction of historic monuments, or fifty other crying Bedlamisms of the time. "E. L. Garbett.

THE OLD HUNDREDTH IN HAWKINS' NOTATION. [278] 8ra,—Your ** Harmonions Blacksmith," gives a version of the "Old Hundredth," and Btates that the bass Stags the diatonic scale in contrary motion, leading oue to infer that the whole of tho bass is the diatonic. In the first strain it wants the sub-domiuaut; in the second strain it certainly is the diatonic scale descending; aud the third and fourth strains are neither ascending nor descending at all. His laying a stress on this partial diatonic scale seems to imply that it helps to make the arraugement a gem. There are English pieces by Attwood, Purcell, Battishill, and Dr. Crotch, that possess this effect, which may be termed a Musical Palindrome; and before which, the "gem" of the "Harmonious Blacksmith" "pales its ineffectual fires." I prefer the old termination of this fine tune to the one he gives; and I cannot understand why the leading note of tho third strain in all the four harmonized parts should be omitted. S. D.

THE SUN. [279] Sib,—I wish to ask the author of the "Astronomical Notes " on what page of the " Nautical Almnnac" is it stated thut the sun is in the constellation Gemini on the 1st July, INTO. On the contrary, we find in that work, as well as in several others on astronomy, that tho sun is stated to be iu a certain sign of the zodiac, and to have so much right ascension and declination. It is, indeed, "nonsense " to infer that he is in a certain part of a constellation from these arcs; becanse the point of intersection of the equator and ecliptic is ever varying. The fixed meridian of Greenwich, as it will be readily perceived by every one who has given this subject any consideration, is not, therefore, a similar case. In thousands of years hence would not " F.R.A.S." say thatthe sun was in the same constellation, becanse his 1!. ascension was found to be quite different > How otherwise, then, I ask can the "inference or conclusion" in question be anything but "illogical." G. Firth.

LUNAR MOTION.

[280] Sir,—I havereceived the English Mechanic since Scientific Opinion has been merged into it, and mnst state that I am much pleaded with the change. I notice a short letter on the above snhject in one of your numbers, and an allnsiou to it by yonr valuable correspondent " F.R.A.S." I should not think it worth while to dwell on this subject any further, but for the very important results which motion produces on the matter moved. It is known that matter moving ronud an axis or centre has a tendency to fly from that centre; and that, in consequence of this tendency, the earth has become an oblate-spheroid, having a greater equatorial than polar diameter.

Now if the moon rotates on an axis passing through itself, it would have the matter at its equator thrown from the centre of motion or axis; and like the earth be an oblate-spheroid, but if it has no such motion, but turns round the centre of its orbit only, the lunar matter will move only in one direction, outward, from its centre of motion, and a prolate-splieroid will be tJte result. Movable matter must pass backward from the centre of motion and leave the side nearest the earth or centre of lunar motion bare, and no air or water could exist on the side of the moon turned to the earth.

Though mnrh has been written on the subject, it must be investigated further; it is too important to be dropped. Noting your great success, Ac,

Toronto. Andrew Elvins.

P.S.—The diagram may help to show my meaning. If the disc A turned round the pivot at the centre D, any movable matter wonld be thrown from the centre towards the circumference, as the small arrows on the disc point. But if a body B revolved ronnd the same centre, and had no rotation round its own centre C, the matter, which would be moved on B, by centrifugal

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ARTILLERY DISCHARGES AND RAIN.

[281] Sir,—Your correspondent "Lex" has misunderstood me. He says, " Supposing, for the sake of argument, that * R. P.'s' theory be correct, I would ask him of what utility would a continuous discharge of artillery, or a gunpowder explosion, be under a cloudless sky?" I never supposed a cloudless sky; I endeavoured to show the utility of artillery discharges under a cloudy sky. We all know what vast masses of clouds, apparently full of water, passed over the country in June aud July, without giving us a drop. This is the time when artillery is wanted. It remains to be seen what discharge of artillery will be necessary to cause rain, this depending in a great measure on the distance of the cloud. I think, if the "inevitable " shower which "Lex" talks about as coming in nine cases ont of ten, had occurred one out of ten in the cloudy weather which I hare spoken of, this subject would not have been started.

I beg to inform " Lex " that I never imagined that a discharge of artillery wonld cause a universal rain. It is not to be supposed that a device of man's can supersede the laws of nature; but surely a shower of rain with a range of 20 or 80 miles would be more beneficial than "Lex's " tank-water. I think, after a few more dry summers, something will be done, unless tho " law" steps in again to prevent it. R. P.

EXPOSURE OF PLATES. [282] Sir,—In answer to " E. T.'s" question, asked some weeks since, allow me to call his attention to a curious discovery recently made by M. Bazin. The time required for the exposure "of n plate is now very short, but if the author's observations be good for anything this time may bo diminished at least one-third by adoptiug the plan to be described. It will excite astonishment to learn that the plan consists in admitting to the camera light which does not pass through the lens. M. Bazin makes four holes iu the front of th" camera, and fits them with glass coloured by a solution of carmine in ammonia, behind which he places another piece of unpolished glass. These holes are uncovered at the same time as the lens, so that the red light falls upon the plate siinnltaneously with the image through the lens. According to the statement of the author the blacks and high lights are by this means much softened and the hall tones greatly improved. The same effect is said to be produced if the sensitised plate be exposed to red light either before or after the picture be token; in the latter case, of course, before the image is developed. This is a matter on which it is impossible to express an opinion without experiments, and we must content ourselves by (tailing the notice of our photographic readers to the discovery. I may mention that M. Bazin has tried other colours, but find* red to be the only one which gives satisfactory resnlts.

J. W.

APPROXIMATELY RECTIFYING THE CIRCLE.

1283] Sir,—I was rather surprised when I learned from "E. L.G.'s" letter (250) that the ratio It had been twice wrongly quoted iu my letter, as respects the sixth decimal figure; because among other items of perfectly useless knowledge, I include my remembrance of the values of », «, and some other constants to the tenth decimal figure. I suppose that, having the 18 or 19 figures in Mr. Drach's letter before me, I simply copied them figure by figure, and farther on in thy letter recopied the resulting figures. An error in the first process might easily occur and remain undetected during the second.

However, I was only writing to point out what I take to be the requirements of a geometrical solutiou; not to underrate the ingenuity displayed in Mr. Drach's arithmetical approximation.

Neither geometrical or arithmetical ingenuity can, I imagine, produce results of any practical value. During the last six years I have gone through a mass of calculations of different orders, mostly involving, more or loss directly, the value of n. But I have never made use auy approximation to the natural value of the ratio, except—iu very rough work—the old

22 fashioned fraction -=-. In all other cases the logarithm of * has alone been of service to me.

Richo. A. Proctor.

LUNAR COSMOLOGY.

[284] Sir,—At present it would be difficult to reconcile in a popular form the conflicting opinions which are entertained by different observers with respect to the modus operandi involved in lunar cosmology. The theory of "LittusHabet Conchas," is one not iu auy way tending to establish a corresponding physital resemblance between the earth and moon; but other observers are all for terrestrial analogies. Before being finally disposed of, would it not be expedient to accumulate additional observations, and not mix up any other subject indirectly with lunar cosmology at the same time? The writer, "Littus HabetConchas," does not allude to any pnblished works as records of observations, but simply a3 the result* of his own observations and deductions. So far from identification with earth-like agencies, "L. H. C." objects to even terrestrial terms of analogy being used with respect to the moon, the points of physical, mechanical, and chemical difference being so great in his estimation. L. H. C.

HANDWRITING.

[285] Sir,—Your two correspondents, pages 469 and 515, appear to me to have missed tho mark. Writing is the medium for conveying ideas to others with the the smallest amount of labour, therefore he who writes the hand or character most easily deciphered gives to his fellows the greatest pleasure or pain quickly. As to the form of character it matters not, so long as it may be read readily by the greatest number or multitude. It is folly to presume that we are in advance of our progenitors, aud history will, I believe, confirm this opinion. If thoy went slowly to work, they thought deeply, took good counsel previous to starting, and then rapidly carried out the ideas well digested.

But as to writing, the substitution of tho steel nib for the quill, caused by degrees a groat distinction in the style of penmanship. It is now necessary to write with a light hand and swiftly. What is tho consequence? Tho strokes of the pen, whether up or down, are light and free; in the haste unnecessarily attempted the terminal letters of each word are much smaller and frequently almost illegible.

That a handwriting in proportion as it departs from clearness becomes stylish, I do not believe. That illegibility is necessary or favoured in commercial circles, I flatly deny, whatever 'may be the presumed rapidity of thonght thereon attendant.

That it takes time to acquire a fairly legible baud, I well know and acknowledge; that it amply repays that labour I believe. Now before me Lies a facsimile of a page of the original MS. of " Ivan hoe," without blot or blemish, so legible that he who ruus may read. In face of this clear round band let us hide our diminished heads. Scriftor.

VULCANIZING INDIA-RUBBER.

['280] Sib,—Several of "our" correspondents have recently asked for information about vulcanizing indiarubber—whether it can bo "re-worked," how it is made, and sundry other matters in connection with this subject. Premising tbat the various processes are Btill somewhat of trade secrets, with your permission I will give the readers of the English Mechanic the facts I have been able to collect.

"Vulcanization,*' as it is called, had its discovery in America. A Mr. Goodyear made a contract for supplying india-rubber mailbags, which he thought would prove to be a permanent article, but found that the heat and colouring matter softened the material and ultimately destroyed the bags- On the occasion of one of his numerous experiments, a piece of the rubber was accidently brought into contact with a hot stove, and was found to *'char," instead of melting, as gum elastic does. Mr. Goodyear proceeded with his experiments, and after trying chalk, magnesia, and sulphur to prevent his rubber softening and sticking, be produced some remarkable results, and the articles being shown about others were induced to try experiments. Among these was Mr. Hancock, the first English patentee, who for some time tried to mix sulphur with the caoutchouc, till, by putting some pieces into melted sulphur in an iron pot and raising the temperature, he found them change, and the lower end of the slips, nearest the tire, turned black, and became hard and horny. The method now practised is to mix caoutchouc with fr«n 2 to 10 per cent, of sulphur, and submit it to a temperature of 270" to 3UU Fahr. A higher degree of beat than this is necessary to produce ebonite. In the specification of the patent granted to Thomas Hancock, in 1843, the process is thus described:—"I melt in an iron vessel a quantity of sulphur, at a temperature ranging from about 240* to 260' Fahr., and immerse in it the caoutchouc, previously rolled into rough sheets or cut to any convenieut form or size, and atlow it to remain nntil the sulphur has penetrated quite through the caoutchouc, which may be ascertained by cutting a portion of it asunder with a wt*t knife. If the operation is complete, the colour of the caoutchouc will bo changed throughout to a yellowish tint. If there is only a margin of yellow around the cut part the operation must be continncd longer, until the colour of the whole is changed, the sulphur adhering to the surface being scraped off; the caoutchouc will then have taken up a quantity of sulphur from one-sixth to one-tenth of its weight." The method of manufacturing various articles is thus described in the specification of the patent obtained in lB4ti:—"When I manufacture these compounds into articles roquiringto be of a permanent shape or form, I make such articles in or upon forms, moulds, plates, eugraved surfaces, or patterns, by pressing, fitting, or moulding such compounds . . . in, ornpou such moulds or forma, and allowing the artic es to remain there exposed to the vulcanizing process, which effectually sets them permanently to the respective forms. In order to prevent adhesion to the mould, I employ silicate of magnesia, either by dusting it on in the form of powder, or with a brush when mixed with water, applied either to the mould or the compound, as may be most desirable."

The "vulcanizcr" itself consists of a strong iron vessel which can be opened to insert the articles to be vulcanized, and furnished with stopcocks so as to apply the pressure of steam. The principle properties of the vulcanized article are nnalterability by climate or artificial heat or cold; impermeability to air, gases, and liquids; facility of being ornamented by gilding, painting, Ac.; insolubility and durability.

The process patented by Mr. Burke consists in the Ubc of the golden sulphuret of antimony to mineralize the caoutchouc. He employs crude antimony ore in fine powder, and converts it, by boiling in water with Boda and potash, into the orange sulphuret of that metal by the addition of hydrochloric acid to the fluid. This compound is combined with caoutchouc or gutta-percha, either together or separately, according to the degree of elasticity he wishes to obtain. The mixture is afterwards subjected to a heat of from 250 to 280J Fahr., and is masticated in an iron box. After one or two hours' trituration the compound is removed, and while still warm is strongly compressed in an iron mould, in which state it is allowed to remain for a day or two, when it is subjected to steam heat for a couple of hours. The block thus prepared may be cut to any desired shape, or into rings, sheets, or threads. This is known as the red rubber, and as it is not liable to decomposition, or to become rotten or brittle, is well adapted for all sorts of valves.

The vulcanite used by dentists is of course made in a Bimilar way to that above described; a caBt of the gums and palate is taken in plaster of Paris, the caoutchouc moulded upon it, and then vulcanized.

It will be evident from the description of the process I have here given that vulcanized india-rubber cannot bo re-worked. All articles are made of the shape they are intended to retain before vulcanization, and any degree of heat less than that at which the caoutchouc was caused to absorb sulphur has no effect on them; whilst, if the temperature be increased decomposition takes place or the rubber is converted into ebonite.

II. U.

CONTRIBUTORS AND QUERISTS.

[287]—Sib.— "M.R.C.S." (a new subscriber) expresses dissatisfaction with a reply given to him in a spirit happily very different from that of most readers. When a question is put for any one to answer, the reply is voluntary and open to any amount of discussion; but when a question is put to any ono by name it is an appeal to the kindness and courtesy of a single individual, and the reply is therefore not a fair subject of complaint, be it what it may. "M.R.C.S." pat me a question thus, a full reply to which would have required quite a page of the closest type, and occupied me two or three hours upon an amount of labour to an already very hardly-worked brain, which if I chose to employ commercially would be worth as many pounds. Such a consideration seldom affects me, and I, with many others, have for several years freely given any information in my power, moved partly by my own delight in science, partly by the earnest wish to forward general enlightment and to fully develop this paper, which is the best national educator the world has ever seen, and a marvellous illustration of the amount of true kindness and public spirit really existing among men. But this gives uo single reader the title to demand a* a right from mo that I shall give him my time, labour, and knowledge, acquired by long aud costly experience. Still less does it give each new reader, when like "M.R.C.S.," hr has taken one number of the English Mechanic, a right to ask me to recapitulate for his sole benefit, and to the prejudice of other readers, subjects which I have already deliberately and carefully treated.

Now for his complaints. He says he has procured Borne numbers I recommended aud is very little wiser; well, that may be my fault ; but, again, it is at least possible that the fault may be with him. He then asserts that I have not described the bichromate siugle cell. It is quite certain that I have done so, but it may be in a number not meutioued before by me (being from homo I cannot refer). His next complaint is more serious—" Sigma's descriptions are not clear enough for the ordinary mind." If this is really the ca^e I shall be very glad indeed if any reader will point out what requires explanation so that I may attend to it. But my papers are written on a definite plan, with the intention, that on completion, they shall be remodelled and published as a book, which it is my ambition to make the most complete and comprehensive possible within a limited size. My plan is to provide a full explanation of principle*, to so educate the mind as to render any details comprehensible whenever met, but to give details only where really valuable. Thus with the sulphate of lead battery, of which my description is specially condemned, I think that any intelligent render, master of the general principles of batteries given by me, would find even that description amply sufficient, but on the other hand, it is quite evident from my remarks that I do not look on this form as worth a detailed description, which if I gave of everything would swell my work into monstrous dimensions. Does "M.R.C.S.." like so many people, imagine that, knowing nothing of a subject, he can by any teacher be put into full knowledge of any special part of it in a few minutes? I may tell all such people that if they vfent knowledge they must work for it with their own brains, any one else can only give them the materials; and if they wish to understand a subject they must go to the roots of it, and not suppose, as in this case, that they can obtain complete comprehension by reading only a few pages out of a systematic series—a series addressed not only to those who know nothing of the subject, but to those principally whoso minds have already been trained by the writer and others,—furnishing all the various branches of knowledge which are needed for perfect comprehension.

Sigma,

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THE EYE AND THE TELESCOPE.

[288] Sie,—There is a prevalent, and in my opinion, erroneous notion with reference to this subject, which I should wish to correct. It is supposed by many that the effects of diffraction are attendant only on vision with the aid of a telescope, as if the telescope were something different in principle from the eye. I would assert that effects precisely similar in kind accompany vision with the naked eye. This applies to the phenomena of spurious discs, Ac. These effects are merely less in degree from want of magnifying power. There is another point on which I would say a few words. I do not think that the advantage to be derived from keeping both eyes open in telescopic observations, is so generally known as it deserves. In order to keep one eye closed a continuous muscular effort is necessary, which, even after practice, causes fatigue. The simplest plan to remedy this is to attach a blackened strip of pasteboard or tin to the split tube of the eyepiece, projecting on both sides. The object of this is to obstruct all light from the other eye, which is kept open. I think this plan has only to be tried for the comfort of it to be appreciated. S. T. Prhston.

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REPLIES TO QUERIES.

♦«* I" their answers, Correspondents art ^1 requested to mention in each inst&noe thi number of the query asked.

A VALUABLE TABLE.—The following table will be found valuable to many of our readers :—A box 24iu. by 16in. square, and 28iu. deep, will contain a barrel. A box 2fiin. by 15jin. square, and 8in. deep, will contain a bushel, A box 12in. by lljin. square, and 9in. deep, will contain half a bushel. A box 8in. by Sin. square, and Hin. deep, will contain a peck. A box Sin. by Sin. sqnare, 4Jin. deep, will contain ono gallon. A box 7in. by 8in. square, and 4-Jin. deep, will contain half a gallon. A box 4in. by 4in. square, and 4J.iu. deep, will contain a pint.

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treadle down the instalment is caused to close; 12' when the foot is lifted the strong spring pulls the WU- * out ai*ain by means of the long lever fixed at the bi» The diagrams explain the rest.—Reed Tlnbr.

[3049.]— REPUBLIC OP GUAIANA.—I am quite *■ tonished at the remark ol "J. G." (p. 490). He s* that I am mistaken in slating that the colonic.* of Quiaare norffc of Venezuela. 1 never thought nor said tha I answered to the query about the " Republic" or Gut* Ha that I believed it was near Venezuela. I think even r; is pnrt of VencEuelan Guiana. I read in the Times *»zc* weeks ago an article about a settlement in that country —Bernardin.

4049.] — GUAVANA OR GUA1ANA. — Besides the ■ ■*- L English error of oinitt in.' tho first A of this uunie, ^ ltt*r iiniti> essential to its sound In any regular

* oepy, "J. G." is very unlucky in limiting the appli<^jxi of what is literally the most defined and natuV-fixed geographical name on any continent in the *•■ ti- It has always applied to the whole river island, -'^►rfcion of South America that the Oronooo, by its -'jue bifurcation, detaches and isolates. Rising about

xniddle of this vast tract, its first course is S.VV. and

iwxird, directly from the sen it is to reach; then, in

tj * urt of the continent, it splits into two, to the S.W.

.N.W., each equal in volume to the Rhine. The

''•iicr called the Cassiquiare, or natural canal, after

. «ling soine lr.n miles, enters the Rio Negro (chief

,-acut of the Amazon) at about 1,500 miles from the

The other branch, tfco proper Oronoco, takes its

^& course, northward, down various cataracts, and then

-. rd, till in about 1,000 miles it reaches the same

»;*« ; and thus wo have the only river iu the known

jrltl that, like Adam's in Genesis, is "parted," and

9Xi compasses a whole land. There are alluvial deltas,

ooune, but nowhere else is a land, a true country,

ui>riaing mountain chains and all other elements of a

ii. .-■•:'". known to be thus moated with river* and sea.

* w the three colonies, to which "J. G." confines the i i i ■ ■. form not one quarter, audby far the worst quarter, » I i i i vast and unique land of Guayana. The southern i i . or all that drains to the Amazon, is Brazilian, but . ■ 11 v trodden as yet. More than a quarter, to the

."W-, formerly Spanish, is now Venezuelan, forming tout half the area of that republic, and praised by

Hi.i'mih as the garden of the world. Its capital has c»t. I ••:>: u moved, but very variously named,beingtheSau

ome and Nueva Guayana of old maps, afterwards u yostura, now lastly Ciudad Bolivar. This quarter,

(ual in extent to France, all drains to the Oronoco.

* fae only low, moist, and unhealthy Guayana is the roi;*iningor maritimo part, comprising the three poor

► lonies "J. G." has alone mentioned, where the i i-itish, Dutch, and French have scratched but the

. i - n i: -i margins of low coast. It is remarkable the gold 1 i^gingb discovered only three years ago in a high and 3 ool table-land of Venezuelan Guayana, had been heard

»f by Raleigh, and fortwo centuries regarded as a fable. E. L. G.

[4131.]— SUNDIAL.—" W. H. C." will llnd a letter on l»n,ge 46j, Vol. X. of the English Mechanic, which may tielp him; also on pp. 520, 582, and 634 in the same Vol., iilso on pp. 11 aud62iuthu Vol. now issuing.—Current.

[41S1.J — REFRIGERATOR.—In answer to "Chico," ice is easily kept a week in the hottest weather by placing it iu a large bag containing plenty of sawdust to *• over and surround the ice, the bag being placed in a liole iu the ground, in a cool spot, and boards being i > Laced over the hole, and old sacks over them. If the sticks are kept damp all the better. 1 always keep ice T, lius, the morchant sending it in a bag of aawdu&t; in tliat alone, it ofteu keeps a week.—Cuurent.

[4170.]-SMOKE BURNING.— There is an article on X-tio above subject, p. 375, Vol. X.—Seuuius.

L4172.J— BORING BAR.—You must construct some iiort of wooden frame to support your bar, and if you take only a small cut at a time no very great rigidity is required. I should take three cuts through a pair of J>rasses. and the last cut not more than l-50in. all round. J.f you take care to lovel tho work first with the spiritlcvel you can at any moment make sure of your bar, Ojao way at least, by the same means, which may save '■ if time in the event of a cutter sticking and breakiutf, or if you think the supports may have given way ;i little by an over strain. 1 once bored a 5in. hole in a L>u.rrel-holding head-stock of a rifling bench thus:—I first fitted on two blocks of hard wood, with a tenon be-low to go between the sides of the bed, and a bedstead bolt or bedscrew to eaeh to hold it down, I then made ii. cutter.exactly like the shifting side of a Franklin's expanding centre-bit—viz., with the Hhaving half of the ordinary carpenter's centre-bit, armed with a nicker on Its outside edgo, and fitted it to the | bar that 1 had previously used for the small holes in the other head of the machine. With this new cutter, and tho bar and heads used before, I bored holes for taking a 2" bar through the block mentioned above. The cutter for the Din. liole was made of a piece of flat bar-steel, drawn out narrow at ono end, and hooked a bit, so as to be like a roughing-out turningtool in effect, and keyed into a hole in the bar. A large carrier was put on end of bar, and a piece of gas barrel about 4ft. long, shipped over the tail of the carrier, formed a lever. On tho other end^of the bar another carrier and an old dog chain with a swivel ■on it, hung over a pulley somedistance off ,with a weight attached, gave the feed. It happened to bo at tho coldest time of a very cold winter, or I should have been -knocked up probably. Of courso if you can lit up an old pedental or two, and run in some type metal or Babbit's metal bearings (or even lead) rouud tho bar, which has previously beeu wedged up to its right place, ho much the hotter; and for heavy cuts you would, of course, not depend on the bearing that fir timber would ■afford.-^J. K. P.

[4174.]— GEOLOGY.—"Veritas's" question cannot bo replied to positively. It must be a time almost beyond computation—million* of years certainly.—AUGUSTUS. [4190.] -EMIGRATION TO THE WEST INDIES.— ii° tuiuSs are to be borue in mind—1, that in the globe's wanner half, viz., in latitudes below SO , no wood clearing (which is the first essential) nor any outdoor manual labour can be performed by Europeans, except at elevations above 8,000ft., or at least u\000ft.; 2, that nature hag not, in tho tropics, made the exploitation of a. labouring class, however poor—and least of all when they are freed slaves or their descendants—by a richer directing class, possiblo as she has here. Now, of the British West Indies (though nearly all are hillior than the summit of Scotland), nono contain grouud high enough for whites to work on, except tho part of Jamaica east of Kingston. On these mountains, I believe that Englishmen, or at least "temperance " men, going there young, might, bosidea their necessaries, raise coffee, and perhaps cotton; but no other of tho present staple exports, which requiro lower and hotter ground. Innumerable wild products of both the high and lowlands, as hard fancy woods, dye stuffs, proserved fruits, oils, and other medicines, ought to be exported; but the miserable social btate induced by two centuries

of slavery, seems to have permanently banished civilized industry. The island nearly throughout is of woudrous, perhaps matchless, fertility and beauty; but seemh of all others the most ruined. The whites have, from being one in ten when the present writer was there, dwindled in a few years, by their own account, to one in forty. Even then, square leagues upon leagues of formerly tilled estates had relapsed into jungle—not what is so called elsewhere, but absolutely impenetrable wood 20ft. Ja*»\ i'—and it must now or shortly differ little in social and physical state from a bit of central Africa, savo in tho negroes having countless herds of half-wild swine, and being under Baptist fetish-men, instead of Obeah ones.—E. L. G,

[4196.]— CEMENT.—"A New Subscriber" will probably find a cement made of resin and beeswax, coloured with Venetian red, answer his purpose. Say about Boa. of resin, |ox, beeswax, and about Joz. Venetian red. Melt it gently and stir it well together; and make both tho bottle and brass cap hot before applying the cement. —Augustus.

[4198.]—CEMENT.—"New Subscriber" will find tho following suit him:—1. Mix a pint of vinegar and a pint of milk: when fullv mixed, clear it of the lumps, and let it settle; then sift into the liquid some quicklime, until a thick paste is obtained. Or 2. Alum and plaster of Paris mixed together, which is a very good cement for glass and brass, and will stand well. Seo ■L*o English Mechanic, Vol X., pp. 137, 391, 417, 463, 513, 640, and obU—Cubrent.

/

[4236.]—DOUBLE STOCKS.-1 quite agreo with 41 Norma " (although only an amateur too) that the best plan to save seed to raise double stocks from is to destroy all flower pips on single flowering plants that have only four petals, and to save tho seed from those with five, six, or seven petals : the more petals, the better the seed, although I never saw a pip with more than seven petals bear seed, and then only on the Giant or Brompton Stock. I never saw more than four petals on a pip of the single-flowered annual Dwarf or Ten Weeks' Stock.—W. E. Coupon.

[4340.] -FROM N. G. LAMBORNE.—N. G. Lamborne's velocipede was a four-wheeler, with the ordinary crank motion, driven by the hind wheels, 8ft. diameter; front wheels, 2ft. diameter; crank, 6$in.; swinging treadles, 6in. joint at crank, and 4in. joint which holds the treadle to the frame near the front wheels; frame 5$ft. long, extreme breadth 22in., driven by the vertical tread of the foot; Beat over the crank, and so high that the foot would just fairly reach the treadle when at its limit downwards. It is a mistake in placingthc seat far away from the driving wheel, and Is a proof of bad management in placing the seat and treadles. I do not advise any one to make after this plan, although it is the best that I have seen, except an invention that is now nursing.

—N. G. LAM BORNE.

[4368.]— LINING-OUT SHAFTING.—Cut a semicircle (exact) of wood, to fit the bottom brass of each pedestal, and mark on tho flat upper side of the wood the exact centre. Set up your pedestals with the wood in, and strain a fine string from one end to the other, to indicate the centro line. Level from one wood in pedestal to the next, and so on with a good spirit level, and block up the short ones with hard wood or sheet lead, till you get them right. Look at your distances apart likewise. Of course tho shaft will be put in its place before finally tightening the base bolts.—J. K. P.

[4408.]—INDIA-RUBBER is th« inspissated juice of several trees belonging principally to the following botanical orders:—Spurge order, or Euphorbiacees; flg and mulberry order; docbane order, or Apoeynea. A complete list of names might be too long, but I beg to quote a few:— (a) Spurge order: Euphorbia antiquorum, nereifolUi, &c, of the East Indies {Soesocraot the Malay), Siplionia elastiea, Ac, of Brazils, Ac. (b) Fig and mulberry order: Ficw* elastica, or Assam India-rubber; F. indica, or banyan tree; F.religiosa; Ctutilloa elastica; all from the East Indies. F. lira*$ii, Western Africa ; F. macropkylla, of New South Wales and Queensland; F. clliptica, radula, prinoidex, Ac, of South America, (c) Dogbane order: Urceola elastica, of Sumatra; Calotropis gigantea, tho well-known Yercum-nar, or jungle plant of the East Indies; N'dambo, and several other lianes of the Gabon; Willugbea edulti, Luii Am, of Bengal, Ac. Many trees of the Sapodilla order or Sapotacea, yield also a milky juice analogous to gutta-percha. I have given (No. 220, p. 272 of our English Mechanic) a note on Balata and Masaaranduba.—Bernardin.

[4418.] FEED-WATER HEATER.—In answer to S. Crompton, I have no means of taking a diagram of back pressure, not having an instrument. But I do not think he understands my note; he speaks of water boing admitted into the heater; I do not call it a heater, as my water is really heatod in the exhaust pipe as it leaves the cylinder. My exhaust pipe is Sin. diamoter; the pipe from cold water pump travels horizontally for a few feet before entering exhaust pipe, both lying horizontally, so that the water shall not bump in all at once but trickle, as it were, out of the pipe into exhaust nearly the whole of the revolution. Now to satisfy myself, thiswoek I took off the head of the heater 12ft. from where the water entered the exhaust pipe and watched the work of it with 101b. of steam, and instead of back pressure I had a partial vacuum whon the greatest rush of water occurred, so much that the steam returned at that particular point with considerable noise; that point can be seen with steam at 401b. In the puffs as they leave the pipe for tho opon air. Again I can get no loud and clear bark from the exhaust when pumping as I can when the water Is shut off, and I certainly think the engine works easier when pumping than not: but one point I do not understand, my exhaust pipe direct from the cylinder is 12ft. long, and when I first tried it in 1863 l blew into a close cask of 130 gallons. Then I had twice as much ailex deposited on its sides as I do now I have replaced it with an iron one as being more orthodox; I presume the reason is because the wood is the best non-conductor of heat.—One Eye.

[4416.]—PHOTOGRAPHICAL.—If "John" is thefortunate possessor of the fourth Volume of the EngLish Mechanic, he will find all he requires, I think, in the exceedingly good chapters on "Elementary Photography," by ?'A- H. W.," on pp. 25, 41, 89, 116, 201, 350, and 285 in that Volume.—GoftUMT.

[4417.]— SAFETY-VALVE FOR KITCHEN BOILERS. —In answer to " Osmond Dobree," a very good article was brought out some time ago (by Mr. Fletcher, Engineer of the Manchester Association for the Prevention of Household Boiler Explosions), which is.said to be unaffected by changes in the temperature. They aro made, I believe, for 10s. each, and cost about 10s. more for lixing, if the boiler is in use. It was illustrated and explained, as every other good thing Is, in this Journal, in the fifth Volume (p. 391, issued August 16, 1867).—

CURKENT.

[4418.]—SILVER COIN.—A Roman Familv Denarius; Family Antania, read ANT. AUG. III. VIR. "R.P.C., rev. LEG. IV. I find it quoted iu one of MM. Lincoln's cntiilogucs, 2s. and Ss., according to preservation. Plated varieties are existing.—Bernardin.

[4121.1— MAKING FLANNEL ADHERE TO BRASS. —One part Venice turpentine to four parts glue, thoroughly mixed, is the best I have tried to make anything adhere to brass.—J. H. P.

[4448.1 TRUE MERIDIAN.—A "Young Surveyor" will find that the best way to obtain the astronomical meridian in the field is by compass, allowing for the variation of the necdlo* which in lh69 at Greenwich was 20 4' westerly. The difference between this valne and that for 18b0 is about 50 (now probably about 1 ). This will not of course apply to any other part of Englaud, but the reply to query 4342 (August 5, p. 477) contains the results of determinations in 1868-9. Practical treatises on navigation give the method of finding the magnetic variation, from which, as just stated, the true meridian is easily found. For the determination of & fixed meridian line refer to p. 285, June 10, reply to query" 3568, Sundial.—W. R. Birt.

[4461.]—SCREW CUTTING.—I am not Bure that onlo is a dictionary word. Perhaps your compositor has done rightly in altering it to into in my letter, on page 525, but he has spoilt ray meaning, while improving ni v grammar. I remember the same thing once before —J. K. P.

[4465.]— TRACING PAPER.-" H. U." may make any drawing or writing paper transparent by damping it with pure and fresh distilled benzine, and it may be used without causing tho ink to run. When dry, the paper resumes its opacity. (See English Mechanic, Vol. X., p. 35; also Vol. IX., p. 897.)—Cduhent.

[4467 and 4551.]—IMPRESSIONS FROM PRINTS AND TRANSFERRING ENGRAVINGS TO WOOD.— Dip a suitable piece of paper into a weak solution of starch and leave it to dry, then moisten with dilute sulphuric acid. The engraving to be copied must be exposed to the vapour of iodine for about five minutes, then applied to tie prepared sheet of paper, and the two pressed together for a minute or two in a copying press. The iodine is said to fix itself on even- part of the engraving covered by printing ink; sucu boing tho case, the remainder of the process becomes evident. I imagine it would be equally applicable to wood. Not proved.—T. W. Boobd.

[4472.]—SOLDERING BRITANNIA METAL.—" J. B~—r" will find a method of soldering any kind of metal without fire, described on p. 525, Vol. X.— Seroitts.

[4473.]— INTENSITY COIL.—I send a rough diagram of a machine made for winding fine wire on to coils. From the following description, " R. F. D." may be able to construct one for his own use. A is a rod that can be taken off the uprights upon which the coil is fixed; C is a wooden rod to carry' the reel that contains the wire; B is a brass tube which has a slit in it from end to end. Inside the tube is A small metal bar, with a thread along Its whole length, and wiiich can be turned upon its own axis. At B is a stud that screws on to tho bar inside tho tube, which moves in either direction whoa

[graphic]

the handle is turned; it also has a small hole in it for the wire to puss through on to the coil at A. It will be seen that when the coll is turned by means of A, it draws the wire from the reel C, through B, which can be brought opposite to any part of the coil. I have made large coils on this machine, and have found but little trouble in winding the wire on to them. The handle on B would bo best at the other end. With respect to the insulation of coils, it may be said that they cannot be insulated too well; yet it must be understood that the inductive influence of the core and primary coil diminishes as the square of the distance; therefore, what is gained by insulation is partly lost through the space it occupies; an insulator should, thorcfore, be used that takes up the smallest space. I think " R. F. D." has not insulated his coil any too well.—J. T.

[4474.]—HORSE POWER.—The common rule for calculating the power of a ateam-engino is 7854 d* p v = 550-horsc power, or <f3 p v = 700-horse power—(a). But as the steam should be stopped off at 3 the stroke .*. <& p v = 933-horso power. This is the simplest general expression; but as a commercial expression, p v can be assumed = 30 x 31 = 93 a constant, which is considered a fair average in calculating the nominal horse power of a steam-engine. Therefore, substituting for p v we

dl have by division da = 10 H. P. .*. H. P. m jg • nominal power of non-condensing steam-engines. And substituting 7lb. per square inch instead of p in equation (a)

d and v remaining as bofore, we find H. P. = ^ —

nominal power of condensing engines. For the actual power of steam-engines, equation (a) must be applied in all cases with properly reduced values of p and v. cither from tables or otherwise. "Tomploton's Engineers*, Millwrights', and Machinists' Assistaut," 4th edition, contains these tables, and much useful information for the practical man.—K. D.

[4474-j—HORSE POWER.—Tho following ie a simple method of Unding the horse power of a steam-engine. bquare the diameter of the cylinder in inches, and divido the product by lli. The result will be the power with steam of 301b. to the square inch. From this, tho power at any other pressure may be ascertained by simple proportion. For example: Required the power of au engine whose cylinder is ton. diameter, supposing the steam pressure to be 401b., 6 x 6 ~~ 12 = 8 (horse power at 301b. pressure). Then by proportion, 80 : 40 :: 8 : 4 (power at 40lb.)—Vebtcxxus.

[4477-1 - BOOKS. — Tho "Encvebpœdia of Rural Sporte," by Delabere P. Blaine, 8vo., 50s., 1852, ami "Youatt on Dogs," 8vo., 6s., 1851, aro both standard works. Mayhcw, Richardson, and Jes« have also written

on tho same subjects.—Cams,

[4478.1—BLUE INK.—1 Chinese blue, 3oz. ; boiling water, 1 quart; oxalic acid, loz. Dissolve the blue in tho water (rain water if you can get it), then add the acid, and it is ready at once. Or 2, dilute sulphate of indigo with water, until the desired tint is obtained. (Sec English Mechanic, Vol. X., p. 163).—Current.

[4479]—COLLODION.—"W. Crawley" appears to handle his plate well up to a certain point—namely, the draining off. He should put down his collodion bottlo, and then gently rock his plate edgewise, keeping the draining corner down. This will cause the ridges to run into each other. I have found it advantageous in this very hot weather to thin the collodion occasionally with a little sulphuric ether.—Paddy.

[4481.]—"A DIFFICULTY."—Tho use of the leather bottom to the cistern is, as explained in the work referred to, for the purpose of keeping the fluid in the cistern always at the same level when an observation is made. Sii.ee the mercury in the tube is almost continually ascending or descending, that in the vessel is

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[4503.]—MENSURATION OF 8UPERFICIES.-The rule " T. W. H." has been try ing for a three-sided triangle, namely, that the area is the square root of the continued product of the half-perimeter multiplied into the three remainders left on taking each side from that half-perimeter, deserves to bo moro used than it is ; being much easier than the statements of the rule commonly make it appear, and the three Bides boing better measurable with accuracy than one side and a perpendicular. So I give, as he desires, every figure of the working of his example; but allow me to nay, a "three-sidedtriangle" was quite conceivable without tho diagram, especially asno use or mention is made by him of D or the line DB:—

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also constantly altering its level, sinking when that in tho tube is rising, and cúr« Pit*«. The adjusting screw may be made to work iu a light brass frame attached to the vessel. The sketch will perhaps afford some idea of the position and arrangement of the screw.—ExhibiTioner At Royal College Of Science.

[4482.]—OVAL.—" Symmetrical Beauty," by D. R Hay, is the best book on the subject I ever met with, ■Sv<>., 6s., 1846. By following his directions I have drawn many ovoid figures, and can safely recommend both the above and the author's other works.—H. В. M.

[4490.]—WELDING CAST STEEL.—If " Т. О. B." will take great pains in heating his steel, by watching it in a nice gentle fire kept free from dirt, and nee the following composition, he will have no difficulty whatever in doing it to his satisfaction :—Take ten parts of borax aud one of sal ammoniac; grind them together roughly, and then fuse them in a metal pot over a clear fire, taking care to continue the heat until all spume has disappeared from the surface. When the liquid appears clear the composition is ready to be poured out to cool and concrete, afterwards to be ground to a fine powder. This may be best done by running it Into a strong iron vessel, or, if in a smith's shop, into a hole in his swaige ; put in a piston, and use tho sledge-hammer. A email quantity of this composition will be sufficient, sprinkled on the parts to be welded while in the fire. Care should be exercised in hammering the splice.— Geo. Jackson.

[4496.]—COPPER COIN.—A coin of Adolph Frederic II., King of Sweden.—Bknar Din.

[4499.]—"FOUL AIR.'—The cause of foul air In mines and other places is the presence of decomposing animal or vegetable matter. Tho gases more frequently present in mines are marsh gas (light carburcttcd hydrogen) and carbonic acid gas. The former is given off to a great extent from scams in coal mines, and is frequently the cause of fearful explosions resulting in great loss of life. This gas, as its name implies, consists of carbon and hydrogen, and has the chemical formula С IIj. By means of the safety-lamp of Sir Humphry Davy, accidents might iu almost all cases bo avoided, for when the proportion of marsh gas is so great as to be dangerous, the gauze cylinder of the lamp fills with flame, and thus warns the miner ere an explosion takes place. Carbonic acid is also frequently present in mines and wells. If a light be lowered into the shaft it will be put out, showing that it would be highly dangerous to venture into such an atmosphere. A short time ago there was an account in the newspapers of some men who unfortunately fell a prey to tho foul gas in a well; this was probably carbonic acid, and the accident might have been avoided by first letting down a lighted candle. Sulphuretted hydrogen is a gas often present in the vicinity of sewers, and is highly poisonous. These gases may bo got rid of by proper means of ventilation. In large mînes there should be two shafts, and if the country be undulating, one shaft opening at the higher and one at the lower level will afford a very effectual ventilation. Blowing engines may also be nsed for forcing pure air into the workings of mines.—Exhibitioner At Royal College Of Science.

237181 showing the next figure to bo 5, and so on He most likely boggled at the second line of the evolution—the line always the most noeding attention. Books do not say, as they onght, that the second figure of a square root must never be written, unie** it beau, nor the second line of computation filled till you have mentally computed the whole third line. In the present case, however, as the doubled first figure of root 4 will not go 10 times in 25, you write 0 for the second rootfigure, put also a 0 after the four, and bring down a new pair of figures, 17. Then, us 40 goes above 60 times in 2517, the next figure of root is 6, and you append a 6 also to the 40, making 406, to be multiplied by 6 and subtracted, and so on. If " T. W. H." tries the triangles 13, 14,15; or 51, 62, 6*8, he will find a terminating root; their areas being commensurable with tho square of a Bide.—E. L. G.

[4504.]—ELLIPSES,—Annexed is a drawing of a simple instrument which night easily be constructed either in metal or wood. The traverse bar А В carries two studs which slide in the grooves of the crosspiece. By turning the traverse bar a pencil point at С id made

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[4511.]product

-WEIGHT OF BALL.—Its content is i the f radiu* and surface; and tho surface = 4oí its great circles. A circle of 7in. diameter being nearly 22 round, has nearly 11 x 3J square inches. Hence the surface of ball is nearly 154, and its content J of 154 * 84 « 179$ cubic Inches, = about 471b. in east-iron, or Б0 in wrought. In the other question, as the circle» aro commensurable, that of 7in. diameter equalling jart 28 x 28 of a quarter inch, a cylinder 7in. diameter and 7in. long would give 784 times 7iu. of the wire; and the. bail, being always $ of its containing cylinder. wiU give $ the above quantity, or 3,658¿in. of wire exactly. When a bull's content only is wanted, 11-21 of tho containing cube is near enough.—E. L. G.

[4512.]—REVOLUTIONS OF BLAST FAN. — The number of revolutions conveyed from one dram to another is inversely a* the diameters of the drnmv Thus, suppose the driving wheel or drum has a dia meter of 6ft., and makes 40 revolutions per minute, and tho diameter of the driven wheel is 8ft., we hjivp 3 : 6 : : 40 : т. Thus x = 80, the number of revolution < of the smaller wheel. Of course, the number of revolutions will be much greater than this in the example proposed by "Ralph," bat the principle is easily applied.— Exhibitioner At Royal College Of Scien-ck.

[4512.] — REVOLUTION OF BLAST FANS.—The method I invariably take to reckon up revolutions oí blast fans might answer Mr. " Ralph." I ascertain, in the first place, diameter of pulleys, likewise number revolutions of first mover per minute. Then proceed» by simple proportion—viz , diameter of pulley on first mover divided by diameter of corresponding pulleyThe quotient, multiplied by number of revolutions of first mover in a given time, gives speed of second mover or counter shaft. Again, diameter of transmitting pulley, divided bv diameter of pulley on fan spindles, the quotient, multiplied by number of révolutions of second mover or counter shaft, gives the speed the Uu is driven at. I have a model of blast fan, the principle of which is quito original, so far as I know. The two sides or cheeks are concaved two-thirds entire width ot fan, with an aperture to admit air; said aperture crossed by a bridge on each side, for carrying fan spindle. The curved blades, formed to suit convex side of cheeks, are secured to a disc. The casing or periphery surrounding disc is placed excentric to same, with breaker? crossing space at variable angles to relieve pressure off fan ; the whole, connected by tie-bolts, with usual method for driving and discharge, needs no comment. Will any of my brother mechanics express an opinion on its merit ?—Williams.

[4512.] —REVOLUTIONS OF BLAST FAN.—Let "Ralph" divide the diameter of driviua pulley nv diameter of smaller one, then multiply resulttuua obtained, by number of revolutions of larger pulley.—W. Bu TiioiiPE, Reading.

[4518.]—HORSE POWER.—Inthie query the pressure of the atmosphere is excluded, as its action and reaction on the indicator is equal and contrary'- Hence the

formula R = "^„vi <D is correct for non-condensing

engines; and, R

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(2J is correct for eon

33000'

p)_ 83000

densing engines. But should the atmospheric pressure be included in the application, the formula H

S (* - .

33000 and R

(1') is correct for non-condensing engines

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ratio of expanslan p 4

The Napierian

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to describe an ellipse by the rectilinear movement of the studs in the grooves. I believe this instrument was described in the Mechanic shortly before its absorption. -T. W. Boord. i -Л. I

[4504.]— ELLIPSES.—I suppose the cheapest and best to be " Cowpcr's Ellipsograph," made by Holtzapffel, because you can strike the curvo (half at a time) with'a pen at once, and its rango is very large, compared with mine, which too, in its present state, is only fit for a pencil. Mine has advantages, for certain purposes, particularly for isometrical drawiug, in which case, as in all others, any true instrument I ever saw, except mine, requires two separate adjustments, with the chance of double error, whilst mino only requires setting for the major axis by a scale attached, and the minor axis must bo right. Mino would cost a great deal more than Cowper's to make. Soe p. 420 for description of mine; also letter No. 140, p. 448, for two other cheap plans, either of which does very well if you take care to have a long connecting-rod, compared with the throw of crank—say 12 times, or 6 times the diameter of circle described by centre of crank-pin. Other machines there are, of which I have one, which makes a half-bred sort of egg shape, but very near a true oval; made many years back, by the late Mr. C. of Halifax, who was a very remarkable instance of a self-made mathematician and mechanic out of a hand-loom weaver. I have seen, also, a parabolic compass bv him, which Is more extraordinary still. "Cowper's Ellipsograph " is on the trammel principle.—J. K. P.

[4511.]—WEIGHT OF BALL.—For the second query of Ralph Williams, it was not stated by any of the three answers, as it should be, that wherever we have to compare one round body with another, as a ball with wire, any reference to n- or its parts, -7854 or *5236, is out of place, and indeed absurd, as the solution will be exact without them, and only approximate where they are used. His bau being 28 times the wire's diameter, Us section is exactly 764 of the wire's section; so that a

4 = SGlb. mean pressure throughout tho stroke which. introduced in formula (1), will give the theoretic R,— R. D.

, [4517.]—STAINING GUT LINES.—I think the best colour to stain gut lines is a kind of greyish green, but it is rather a troublesome process to undertake. Boil и. cupful of black tea in a quart of water, allowing tho gut to remain in till it has acquired what is called the "redwater stain," when it should be rinsed in cold water und allowed to dry. Then put a handful of logwood chipe into a quart of water, and boil till the latter is reduced to a pint. Take It off the Arc and throw into it apieor blue vitriol previously powdered; stir until the copperas is dissolved, when the gut may be put in and kept there till it acquires the desired tint. It will not take many minutes, and the gut should be rinsed in clean water directly it is taken out of the dye. For a slate-coloured stain, which many prefer, a mixture oí boiling water and ink is amply suflieient, always remembering to wagh the gut thoroughly when the right tint U obtained. Out can likewise be coloured by any of the aniline dyes sold at the chemists, but I think they might possibly injure its texture.—A. T., Staines.

[4518.]—MYROBALANS.—This is a fruit which grow* in India, and is largely imported to Europe nu account of the tannin which it contains. The myrobaUu is of a pale buff colour, and resembles a slightly shrivelled plum. It consists of fibrous cellular matter enveloping a stone. It is hard and firm, and when beuten with a hammer breaks up iuio irregular fragments and a light-coloured dry powder. As myrobalans are cheaper than galls and stronger than sumac, they are rapidly superseding those articles. With preparations of iront they dye cotton stuffs a fuller black than cau be obtained by sumac—Dykk.

[4518.] — MYROB ALAN. —A kind of dried plum brough t from the East Indies, where it is need by the Hindoo;* in medicine and calico printing. It has au unpleasant bitter taste ; produces with iron a durable black dyo an.I ink, and with alum a dark brownish yellow.—T. W. Boord.

[4518.]— MYROBOLANS.—Myrobolansia a bitter fmit brought from India, and used by calico-printers, dyers, Ac, for dyeing black and yellow.—Bkacox Locoh.

L9-1—PHOTOGRAPHY.—Procure some pood benplace it in a plate and apply moderate heat until Luito fluid, pour it into a cold plate and when quite ■ t may be broken in pieces. Then dissolve loz. of isorl hcuzoin in 8oa. of methylated alcohol and 20

*< of HRiidarae. Then add 20 drops of mastic

>*li, mudc bv melting gum mastic and adding tur

no to it whilst iu utluid state. The impurities will

nettle, and it is ready for use. Should the varnish

• thick add more Bpirit.—H. J. Kikoham.
20,J —PERCH FISHING.—I think the best time to
U»r porch is from September to January in large deep
3t4 and ponds by the side of a river. There are
»>ors oT these iu the Thames, and excellent perch
rig iu to bo found near the paper mills at Tciuplr,

3iurl-»w. Weirs are the best places in suniiner

, but perch are not in first-rule condition then. re are several methods of fishing for them, and of •ho different kinds of tackle. 1 think the most suelul in. the T names is the method known as "patereriritf." Attach a lead to the und of a gut line about t»r 5ft. 1-jug, and about 3iu. aud lOin. above it two rfc pieces of gut, about 4in. or 5in. long, with No. 8

hooks fastened so as to stand out at right angles, t. with ;i live minnow or gudgeon—the hook put ,ugb the upper lip. A longish rod, with a free-running , I have always fouud the best. I prefer the plaited lines myself, as those made of silk and hair " kink" ineutly and are very apt to hitch instead of running I

3 besides, they are not so stroug as the plaited silk. | pered at all.—J. K. P. ten all is prepared, with the lead hanging Gft. or 7ft. i 14546.]—DIVISION Tii the top of the rod, drop the line gently into the tor till the lead rests on the bottom. Shift the bait ery now and then; don't strike diroctly you feel a itch, but "bide a wee,'' and when you feel a second (ftCk tightentho line, aud give a sort of "lift," as the rch is rather a delicate-mouthed fish, and if you strike" hard you are apt to lose both fish and bait. »rch generally' swim in shoals, so if you succeed in ruling one keep to the same place. There is another othod of fishing for perch, which consists in halting itn brandlings, and using cither ordinary tackle or the ottingharu style. A few broken worms thrown in now ud thou will otteu attract the fish. Iu these methods it the float be carried well under before striking.—A. *., Staines.

£4521.] — EXTRACTING HONEY FROM THE COMB. — Jut tho comb in pieces with a sharp knifo so as to .ivide all the cells, and place tho pieces in a colander »ver a basin or jar to receive the honey as it drains off.—

T. W. BOOBD.

14522.]— PURE CHARCOAL.—I am rather puzzled by Jr. Ibbotsou's query. Doos ho mean what we, as he mists, call pure charcoal, or what druggists sell as uch—a very serious difference? Pure carbon is almost mpoasible to obtain, except in the form of the diamond, rut a ** pure vegetable charcoal" is made by carbonizng willow or other wood in an iron retort. I imagine * What kind of tire and hot plate is pure?" must refer to this. For such a purpose, with an iron retort tilted with an exit sufficient ouly to give vent to the gases, any fire will do, but tho purest Are in ordinary uso is a spirit lamp. For small quantities a piece of gas-pipe, plugged at one end and partially closed at tho other, would s-jrvc. N.B.—The "purity" of tho charcoal is a superstition, and has nothing to do with the effects.—Sigma.

[4534.1— STEAM JOINT.—" Schemer" will overcome the difficulty he has experienced in obtaining a perfectly tight joint by having a joint made exactly like a universal swivel of a gas bracket. He cau bring tho L»oUor noarerto the engine, or vice versa, by a telescopic joint made secure by a stuffing-box.—1>. Clarkx.

[4528.]—CARVING AND TURNING SOFT WOOD.— For external surfaces use the gouge and chisel. Thcin*ides of boxes, &c, are ahaped aud finished with what are called hook-tools; then-form varies with the taste and requirements of the operator, and considerable practice is necessary to use them properly. The screws «to cut with a rough kind of traversing mandril. Tho tools used for carving are small gouges, chisels, &c, of various shapes and sizes.—T. W. Boord.

[4529.]— CHAIN ADJUSTMENT TO COMPOUND MICROSCOPE.—This is a very simple and efficient movement, and consists merely of an endless chain working round two pulleys, one"of which is furnished with a milled head. The chain is fixed to the "body" of the microscope midway between its extremities, and also between the pulleys. "S." will easily comprehend its working from litis brief description. If not, let him devise the wurkiu-' of a ship's rudder by the "wheel"— tho principle* are the same. As regards its accuracy: I will focus a 1-12" with it, and do nightly use an \" without difficulty. So far as/ociiMtnr; is concerned, the rtno movement may be dispensed with where the chain movement is used, but the fine movement, if well made, w usefulfor micrometrical purposes, aud should always be applied where expense is not of vital importance.— H. P.

[1539.] —CHIMNEY.—If you build a chimney for four largo boilers and determine to have a good draught, choose any form—round or octagon is the best—let it be 40 to 50 yards high, 5 yards in diameter at the bottom, and t>walUl imide, most decidedly, all the way to the top.— Wamshof.

[4540.]-MOUNTING PLANE MIRROR IN REFLECTING TELESCOPE.—Mr. A. Whites plan would fail. Hersehel shifted the optical axis of his telescope parallel to the tube, and so brought it close to the side. M.r; White shifts his angularly within the tube, which wdl have uu other optical effect than ho could get by rutting the tube with tho mirror. If he will consider his picture he will see that, without aoino as vet unknown virtue in the tube itself to force the mirror only to show objects towards which the tube is directed, he would only see just such objects us he in the direction of the axis of the mirror; and very little of them, since he gets tlie tube (the lower half in his figure) iu the way, and ouly the extreme upper edge of Ms mirror (as suowii m tho figure) would bo available to form an image.—R. A. Proctor,

[4543.]—TORTOISE-SHELL COMBS.—The edges of tho fracture should he scruped smooth, so as to overlap each other, And freed from greate, then dipi'cd into hot water to sottcn them, pressed together with hot tongs, and lastly, plunged into cold water till hard again.—T. W. Boom).

[4546.]—LATHE, Ac—TO " BIERLALA."—If you are limited to three rows of divisions, I think 180, in'., si, are perhaps the best. I am strongly iu favour of a row containing 11,13, 17; alsu Vi audit, if your diameter is sufficiently great, else the 6th and 7th of tho 17 row come too close to the 9th and 10th of the 19 row, unless your holes are extremely small. Less than 7ln. diameter will scarcely Irold them. I have this verv day done the fitting of my now double bearing mandril, and got the loose collars and nuts into their places. It is a first-class job for a good hand, and I think very few amateurs would venture tojtry it—single-handed I mean, of course. My hardened fast-collars are coned with the slide rest set 1tnper for the inside of collar, and Adeg. or UOmin. taper for the outside of collar and the inside ot cast-iron fitting. I do not shrink the collars in by heating the casting, but I put a strong bolt through the hole in the collar, to draw it into its place, and assist its progress by blows of a heavy mallet, while tightening the nut, each collar separately. Do not put one long bolt right through from front to back, or you may break Your casting, unless indeed you put a good stout prop In to support the train. Your " 35 " in the hist line appears to he a misprint. The loot? collars fit tight on to tho cylindrical portions of the mandril, and are adjusted by screw nuts. I do not intend to have the work japanned, as I have heard of collars being tempered or losing some of their hardness through excess of heat employed. Mine are as hard as I could make them, and not tem

PLATE.—The nnmbers of the division plate which I find most useful are

720 360 200 144 180 113 96

divide into differences J3 3 *° » £ * * i 11 may add that Edwin Baker, of 14, Mount-row, Berkeley-square, London, issues a list gratis of the '* Ready Reckoner for tho Dividing Plate;") but there are also found useful for some amateurs who do very fine work these numbers, say—

180 136 divide into differences °* ■* and HoUzapffeTs lathes, to soino of them were put these individual numbers, 221, 209, for vory fine rings or flutes, when you UBe thom all. The other parts I cannot reply to.—Wahsrof.

[4547.]—A FIELD OF BARLEY GROWN FROM OATS.—I think this matter is referred to in "Vestiges of Creation," but has been little discussed; if true, as it most likely is, it is an illustration of "natural selection," and its cognate doctrines, showing how natural species aro formed and modified by surrounding conditions.—SlOMA.

[45-17.]—A FIELD OF BARLEY GROWN FROM OATS.—" S. G." will find, iu the "Vestiges of the Natural History of Creation " (see p. 144, Ed. 8,1850), the following much earlier mention of this subject:—" It is now fully ascertained that the various bread-forming grains, wheat, barley, oats, rye, are resolvable into one. if wheat be sown in June, and mown down Bo as not to be allowed to come to ear till the next season, tho product will be found to consist partly of rye or some other of tho cereals. Oats have in like manner been transformed into rye, barley, and even wheat. Till a recent period, this phenomenon was doubted; hut it has been tested by experiment, and reported on by so many credible persons, that it can no longer be rejected. Aud it appears that poorness of soil has the same effect as mowing down. One observer states that, in a field of wheat, near Lucerne, ho saw ears resembling barley, but with grains similar to rye, growing from the game item with eart of wheat." The author refers to the Gardener*' Chronicle, 1846, pp. 118,102, and August and September, 1<*44; also Afar/. Nat. Hift. new series, 1. 574; and Itep. Roy. See., 1846, p. 381—W. P.

[4548.]— IMMERSION LENSES.—These lenses possess the great advantages of being easy to work, ar.d of possessing greater "penetration" than a "dry" lens. Their price will vary from £3 for a German l-16in. to £50 for an English l-50in. of first-class make. If "M. J. C." be a young beginner, and is contemplating the purchase of an '■ immersion," let him take to heart Punch'A advice to persons about to be married—" Don't 1" He will find an English Jin. answer all his requirements for some years. If he be an experienced microscopist, he cannot do better than read up the Microscopical Journal for the present year and form his own conclusions as to the suitability of, this kind of lens to his requirements. Any of our leading makers would show him their working. An English Jin. may be purchased for about £4, hut I question the utility of applying the immersion principle to lenses of these long foci.—H. P.

[4552.]—AVIARY.—Tho boat timo for purchasing birds to keep in an aviary is the fall of the year, now rapidly approaching. This of course applies to such birds as the bullfinch, chaffinch, linnet, greenfinch, reed-sparrow, yellowhammer, &c, which are more likely to live when taken in the autumn. Canaries, being bred under domestication, may be obtained at any time, and are undoubtedly the best birds for aviaries. If " Rebaf" purchases any, let him get the Norwich birds, or the Yorkshire—German ones seldom live moro than two years in this country. Goldfinches are also excellent birds to keep, whether on account of their song or their hardiness. Some of them will pair with canaries, producing what are known as "mules," probably the best song-birds known in this country. The siskin is a pleasing bird, with a peculiar song. It much resembles the goldfinch in form and habits, bnt its notes are inforior, although it sings from the early morning to the late evening. It is very hardy and often lives eight years in a cage. The linnet, of our field birds, 'is perhaps the sweetest songster, and if taken about October will soon become tame. If taken in the spring it Is not likely to live long in a cage; besides being an extra cruelty, as most of them hove either young or eggs at that season.—S. G.

[4554.]—PENDULUM.—Your correspondent "Vibrator" has discovered a "mare's nest." He wishes to kuow " why a clock should gain time by raising the bob, as by the law a longer swiug should be accomplished in tho same time as a shorter one V" the law being, as he says, that a wcigbt suspended by a silken cord will move in unequal spaces iu equal limes. In so far as the law of pendulum motion, he is iin a sense correct, although ntntod in suxh u tomuion-j I ice manner. Yet he fails to

see that the unequal spaces do not refer to the length of the pendulum, but to the length of its swing,—thai Is to say, that a pendulum may vibrate in an arc of 7- or an arc of 4 , audits oscillations be isochronous or nearly so. Tho raising of the bob shortens the centre of oscillation of the pendulum, and thereby shortens the timo of its swing, but makes no alteration in the time it takes to oscillate in a largo or small arc of a cycloid, or in a small arc of a circle. Your correspondent should read "Clock and Watchmaking," by E. B. Deuison, M. A.—Electro-magnet.

[4554.1—THE PENDULUM.—" Vibrator" is in orror respecting the pendulum. The following are amung the laws of the instrument:—1. At the tame station, pendulums of the name length move through atcloidal arcs, whether long or short, in the same time. Common pendulums, which Oicillate in circular arcs, practically possess this property when their arcs do not exceed5 or 0". 2. Tho times of oscillation of pendulums of different length*, vary as the square roots oi this length. Thus, if at the same station, one pendulum be four times the length of another, it will take twice as much time to make its oscillation; if nine times the length, thrice the time; and so on. If, therefore, the bob be raised or lowered from any cause, the clock gains or loses accordingly ; and hence the necessity for compensation pondulums.— W. P.

[4563.]—BRASS COIN.—This Is a jetton or counter of the timo of Queen Anne. They were used for calculating. Tho word "jetton " is derived from the French verb jitter, to throw or cast; hence to cast up an account.—T. W. Buohd.

[4567.] — MATHEMATICAL INSTRUMENTS. — Broken instruments are hardly worth repair. The plates are steel and brazed in, and could hardly be got out. Excellent French and Swiss cases of instruments are to be had for a song at the second-hand shops. A friend of mine bought a splendi d set some time since for 30s., bnt there seems a prejudice against them. The pens are never so good as EUio tt's, but whose are?—J. k. P. [4570.]—A LEGAL POINT.—Your querist "Ironmonger " does not give any hint as to what part of the three kingdoms the county is situated in which he carries on his business; and as the law regarging the dealing in second-hand goods, old metals, bones and rags, differs so essentially in England, Ireland, and Scotland, and there are besides so many local acts in various towns, that it is almost, if not quite, impossible to give him a satisfactory reply. When he writes again, giving his locu-i, I may then advise him on the legal point. In the mean time, my advice is that he do not trust to the dictum of any " common " policeman, but go to head-quarters aud soothe inspector or superintendent, and aBk to see the Act under which their subordinates are acting as to the matter of buying or taking old metal in exchange; and I have no doubt either of these gentlemen will have the courtesy (as I would) to show their authority for the restriction; and if there is aa act, your correspondent on reading it can judge by his own common sense whether the local guardians of the peace and public morality have misconstrued the meaning thereof, or are otherwise acting capriciously towards him and others who may also be so circumstanced.—Electro-magnet No. 1.

[4570.]— A LEGAL POINT.—In the 32nd and 33rd Vic, cap. 99, ' Tho Habitual Criminals Bill,' sec. 17, it is enacted:—" Any dealer in old metals, as defined in the Old Metal Dailers; Act, 1861, who shall either personally or by any servant or agent purchase, receive, or bargain for lead, whether new or old, in any quantity at onetime of less weight than 1121b., or who shall personally or by any servant or agent purchase, receive, or bargain for copper, whether new or old, in any quantity at one time of less weight than 561b., shall be liable to a penalty of £5, to be recovered in the same manner as penalties Incurred under the said recited act are therein directed to be recovered." It is evident from this that the police have informed you correctly, you being a person dealing in such metals.—Thomas Powlson.

QUEBIES.

[4572.] —GEOLOGICAL.—Near Malvern arc some limosto.-.e quarries. Can any of your numerous correspondents inform me to what formation they belong ?— Philosophkr.

[4573.]—METHYLATED SPIRIT.—Can" An Associate of the Royal Schoolof Mines," "Beta/* or any other readerof the English Mechanic, inform me if there is, at time*, any difference made in the quantity and quality of the wood spirit which is added to the spirit of wine? Some samples I have succeeded in freeing from the smell of naphtha, others I cannot by the same process.— M. M.

[4574.]—PAR AFFINE OIL.—Can any brother reader of the English Mechanic inform me if there is any mixture that can be added to inferior paratnne oil to cheapen and improve it for burning in lamps 7 —A Poor

M ECHAXIC.

[4575.]—ENAMELLING WATCH-CASES.—Will some other reader kindly inform me how enamelling is done on the backs of gold watch-cases, Ac?—E. J. R.

[4576.]—BLACK BRASSWORK OF MICROSCOPE.— Will some of our kind readers inform me what the inside of the tubes and other parts of the brasswork of microscopes and telescopes is blackened with? If they would give a short description of the process it would oblige.— J. Haines.

[4577.]—INDUCTION COIL.—TO "SIGMA."—I want to make an induction coil, and feel rather bothered with so many plans of construction that have been recommended. "Inductorium" stated lately that the greatest inductive effect was at the centre of the coil, and nil at the two poles. Is it so, or not? If so, a partition in the middle of the coil would cause a loss of the best part of the electro-magnet. Will paper, soaked iu parafnno, answer as well as gutta-percha tissue to insulate the layers? and how much would be required? But if "Sigma" would give a working description of what he considers the bcM plan of coil to give a spark Sin. or 4in. with 4 Bunsen's cells, he would oblige.—Operator .

[4578.]— STRETCHING GUT-BAND—Is there any way of permanently stretobint? n new gut-band 2iu., which is about 8 vards long, w.i 1 Uu. in diameter-?—

T. i:.

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