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1ечв cvery-day electricity iudeed, and hence their value as lightning prcventors, nnt attractors. Yon can discharge, silently and without shock, the largest electrical battery, by simply holding one pole while you present a sharp needle toward the other. In this way there is no doubt every right lightning conductor helps in a storm to discharge the cloud silently, and prevente Hashes that would, without it, have occurred. Hut in the excessive tension of stonn electricity this purpose ia no better served by delicate needle points than by the accidental raggedness of any metal termination. Every experimenter knows this is the case even with an electrical machine in good order. Doubtless there is a difference between the action of Messrs. Ne wall's beautiful "attractors" aud a broken bar end iu »unshine, but not iu a storm. If anything can be said to attract lightning it is the poiutedness of the whole building or rising ground. Spikes make no difference, or knobs as big as any dome; and nothing can he more absurd than carrying out conductors an inch above or beyond what they are to protect. (The poor Duke of York is spitted on the top of his column !)

4. Insulation is equally preposterous, as your second answerer perceives. It is abundantly proved the electrical passage will never turn aside from the line of best conduction.

ft. For his "taken deep enough Into the groumi," road simply, "taken to the next metallic mass that has metal communication with the ground." As every nixlem English building has metal water-pipes from the ground up "to the metal gotten," it is so far absolutely protected already. Accordingly, I defy yon to cite a case of damage by lightning in all England, in this century, outside a building and below the level of its gutters. They are cither on the outside, above all gutter», or inside, by descending a chimney. No conductor! to the ground then are ever wanted,—you have them already—but simply from chimney tops, or other "attractors," to the nearest gutters. Whatever metal then yon see spent ander colour of lightning protection, lower than the highest gutter level, is merely jobbed in for "percentage" by quacks, patentees, architects, ci hoc genus ovine, that the mighty wisdom of Mr. John Bull creates as his ornaments aud oracles, his percentagers. I saw once a poor (not in benefice) parson, whose school-house was being lightning condnctored entirely comme il faut—pointed attractors of highest finish,—"the insulators that F. Bedford would kl -civ imitate with " bottle-necks,"—and all. Being a tine day, as they carefelly brought the work downwards, before connecting with the ground, it gave beautiful sparks, of course to the astonishment of bii reverence, the M.A., whom Oxford had never informed of such a thing as electricity, and of course that showed beyond question that all is right, and we are in the hands of men of true science. Could he or his builder have made sparks appear from the rods? What could be more с juvincing or satisfactory that what is here spent is well spent? Now this could only be done, observe, with finely sharpened "attractors" and good insulation. Hence you вое what all this is wanted for.

6. But though conduction is needed only to the gutters, please observe it is needed from every poiut liable to be struck. Cases innumerable have exploded the old French error that one point—the highest—will protect the rest of an object. Ships with every mast protected have been struck on the end of a yard. All we can say is that no case is known of lightning striking a point within or behind the plane of three others, or 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 ascertainable as the number and position of letter-boxes, or of barber's shops. On St. Paul's Cathedral there are four; on Westminster Abbey, seven ; ou Salisbury Cathedral, six. To know precisely the points needing protection, nil 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 large as it would stand upon. Whatever poiut you could touch with the centre of this plane, without touching other points, is a point liable to lightning stroke, and no other point is liable. So at least we have a right to say, till some instance be adducible of a poiut not thus defined being struck. Protection from lightning, therefore, is just as simple und absolute as exclusion of rain from a building, and it is iti.fr11 v wanton and inexcusable that such a thing as injury to a public building by lightning, in а civilized country, should ever occur or have occurred in this generation. Nowhere but among percentagers could it now occur, any more than destruction of historic monuments, or fifty other crying Bedlamisms of the time. E. L. Gabbett.

THE OLD HUNDREDTH IN HAWKINS' NOTATION.

[27Я] Sib,—Your " Harmonious Blacksmith," gives a version of the " Old Hundredth." and states that the bass sings the diatonic scale in contrary motion, leading one to infer that the whoh* of tho bass is the diatonic. In the first strain it wants the sub-dominant; in the second strain it certainly is the diatonic scale descending; and the third aud fourth strains aro neither ascending uor descending at all. His laying a etress on this partial diatonic scale seems to imply that it helps to make the arrangement a gem. There are English pieces by Attwood, Pnreell, BattisbiU, and Dr. Crotch, that possess this effect, which may bo termed a Musical Palindrome; aud before which, tho "gem '* of the "Harmonious Blacksmith" "pales its ineffectual fires." I prefer thy old termination of this fine time to the one ho gives; and I cannot understand why the leading note of the third strain in all the four liarmonized parts should be omitted. S. D.

THE SUN.

[279] Sin,—I wish to ask the author of the "Astronomical Notes " on what page of the " Nautical Almanac " is it staled that the snn is in the constellation Gemini on the 1st July, 1м"0. Ou 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, aud to have so much right ascension and declination. It is, indeed, " nonsense " to infer that he is iu a certain part of a constellation from these arcs ; becanse the poiut 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.B.A.S." say thatthe sun was in the same constellation, Ьесаиве his \\. ascension was found to be quite different 1 How otherwise, then, I ask can the 11 inference or conclusion" in question be anything but "illogical." G. Firth.

LUNAR MOTION.

[280] Sib.—I havereceived the English Mkchanic since Scientific Opinion has been merged into it, and must state that I am much pleased with the change. I notice a short letter on the above subject in one of your numbers, and an allnsiou to it by your 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 motten produces on the matter moved. It is known that matter moving ronud au 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 he an oblate-spheroid, but if it has no such motion, but tnrns round the centre of its orbit only, the lunar matter will move only in one direction, outward, from its centre of motion, aud a prolate-splieroid trill be the result. Movable matter must pass backward from the centre of motion and leave the side nearest the earth or centre of lunar motion hare, and no air or water could exist ou the side of the moon turned to the earth.

Though much has been written on the snbject, it must be investigated further; it is too important to be dropped. Noting your great success, *c,

Toronto. Andrew Elvtns.

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 would be thrown from the centre towards the circumference, as the small arrows on the disc point. But if a body В revolved round the same centre, and had no rotation ronnd its own centre C, the matter, which would be moved ou В, by centrifugal

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ARTILLERY DISCHARGES AND RAIN.

[281] Sir,—Your correspondent "Lex" has misunderstood me. He Bays, " Supposing, for the sake of argument, that 'R. P.V 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 nnder a cloudy sky. We all know what vast masses of clouds, apparently full of water, passed over the country in June and July, without giving us a drop. This is the time when artillery is wanted. It remains to be seeu 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 out of ten, had occurred one out of ten iu the cloudy weather which I have spoken of, this subject would not have been started.

I beg to inform "Lex *' that I never imagined that а discharge of artillery would cause a universal rain. It is not to bo supposed that a device of mau's can snpersedo the laws of nature; but surely a shower of rain with a range of 20 or 30 miles would be more beneficial than " Lex's " tank-water. I think, after a few more dry summers, something will be done, unless the " law" steps in again to prevent it. R. P.

EXPOSURE OF PLATES.

[282] Sib,—In answer to " E. T.'s" question, asked some weeks siuce, allow me to call his attention to a curious discovery recently made by M. Bazin. The time required for the exposure of a plate is now very short, but if the author's observations be good for anything this time may be diminished at least one-third by adopting 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 in the front of the camera, and fits them with glass colonred by a solution of carmine iu 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 npou the plate simultaneously with the image through the lens. According to the statement of the author the blacks aud high lights are by this means much softened and the half 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 he taken; 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 calling the notice of our photographic readers to the discovery. I may mention that M. Bazin hos tried other colours, but fiods red to be the only one which gives satisfactory results.

J. W.

APPROXIMATELY RECTIFYING THE CIRCLE.

[28ft] Sib,—I wae rather surprised when I learned from " E. L.G.'s" letter (250) that the ratio irhad been twice wrongly quoted in my letter, M respects the sixth decimal figure; because among other items 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 I'.i figures in Mr. Drach's letter before me, I simply copied them figure by figure, and farther on in lit ■ letter recopied the resulting figures. An error in the first process might easily occur aud remain uudetected during the secoud.

However, I was only writing to point out what I take to be the requirements of a geometrical solution; uot to underrate the ingenuity displayed iu 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 less 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

83

fashioned fraction -=*. In all other сазе* tho logarithm of » has alone been of service to me.

Richd. A, Proctor.

LUNAR COSMOLOGY.

[281] Sib,—At prosent it would be difficult to reconcile in a popular form the conflicting opinions which are entertained by different observera with respect to the modus operandi involved in lunar cosmology. The theory of "Littus Habet 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 aualogies. 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 sometime? The writer, "Littus Habet Conchas," does not allude to auy published works as records of observations, but simply as the results of his own observations aud deductions. So far from identification with earth-like agencies, "L. H. C." objects to even terrestrial terms of analogy being used with respect to tlu moon, the points of physical, mechanical, and chemical difference being so great in his estimation. L. H. C.

HANDWRITING.

[285] Sib,—Your two correspondents, pages 4П9 and 515, appear to me to have missed the 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, and history will, I believe, confirm this opinion. If they 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 the steel nib for the quill, caused by degrees a great distinction in the style of penmanship. It is now necessary to write with a light hand and swiftly. What is the consequence? The strokes of the pen, whether up or dowu, are light and free; in the haste nnnecossarily attempted the terminal letters of each word are innen 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 thought thereon attendant.

That it takes time to acquire a fairly legible hand, I well kimw ami acknowledge ; that it amply repays that labour I believe. Now before me lies a facsimile of a page of the original MS. of " Ivanhoe," without blot or blemish, so legible that he who runs may read. In face of this clear round hand let us hide our diminished heads. Scriptoh.

VULCANIZING INDIA-RUBBER.

[286] Sir,—Several of "our" correspondents have recently asked fur information about vulcanizing indiarubber—whether it can he "re-worked," how it is made, and suudry other matters in connection with this subject. Premising that the various processes are »till somewhat of trade secrets, with your permission I will give the readers of tue 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 wan 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, he 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»m 2 to 10 per cent, of sulphur, and suUmit it to a temperature of 270i to 800J Fahr. A higher degree of heat than this is necessary to produce ebonite. In the specification of the patent granted to Thomas Hancock, in 1H48, the process is thus described :—" I melt in an iron vessel a quantity of sulphur, at a temperature ranging from about 240° to 250^ Fahr., and immerse in it the caontchouc, previously rolled into rough sheets or cut to any convenient form or size, and allow it to remain until the sulphur has penetrated quite through the caoutchouc, which may be ascertained by cutting a portion of it asunder with a wet knife. If the operation is complete, the colour of the caoutchouc will be changed throughout to a yellowish tint. If there is only a margin of yellow around the cut part the operation must be continued 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 ouo-sixth to one-tenth of its weight." The method of manufacturing various articles is thus described in the specification of the patent obtained in l»4b' :—" When I manufacture these compounds into articles requiring to be of a permanent shape or form, I make such articles in or upon forms, moulds, plates, engraved surfaces, or patterns, by pressing, ilttiug, or moulding such compounds . . . in, or upon such moulds or forms, and allowing the artic es to remain there oxposed 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 "vulcanizer" 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 unal ter ability by climate or artificial heat or cold; impermeability to air, gases, and liquids; facility of being ornamented by gilding, painting, 4c. ; insolubility and durability.

The process patented by Mr. Burke consists in the uso 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 soda 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 ia afterwards subjected to a heat of from 250' to 280° Fahr., and is masticated iu 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 similar way to that above described; a cast 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 be rc-worktd. All articles are made of the shape they are intended to retain before vulcanization, and any degree of heat loss 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.

H. U.

CONTRIBUTORS AND QUERISTS.

['287]— Sin. — "M.R.C.S." (a new subscriber) expresses dissatisfaction with я reply given to him in a spirit happily very different from that of moist 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 one by name it is an appeal to the kindness and courtesy of a single individual, aud the reply is therefore not a fair subject of complaint, he it what it may. "M.R.C.S." put 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 enlightmcnt and to fully develop this paper, which is tho 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 no single reader the title to demand ал a right from me that I shall give him my time, labour, and knowledge, acquired by long and costly experience. Still less does it give each new reader, when like "M.R.C.S.," he 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 some numbers I recommended and 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 single cell. It is quite certain that I have done so, but it may be in a number not mentioned before by me (being from home 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 case 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 aud 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 principles, 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 reader, 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 euch people that if they want 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 pagos out of a systematic series—a series addressed not only to those who know nothing of the subject, but to those principally whose minds have already been trained by the writer and others,—furnishing all the various branches of knowledge which are needed for perfect comprehension.

Sigma.

EXTRACTS PEOM 00BEESP0ITOENCE.

A WORKMAN'S TESTIMONY.-^Joseph MIlUnsrt<m. rf Brunswick-road, Sheffield, says :—" 1 have t»c-en anxirrti* for some time to express my approbation of 'oars,* uuft add any testimony to its value. But judging from the tone oí some of your recent * Answers to Correspondents.' I have subscribed to maiiv and varions periodicals for about twenty years, but f never ilerivswd such satisfaction from one before. There are {to me) many points of interest contained therein. Агпогцг-i the rest being the articles on 'Chemistry,' * Elec trinity/,' * Science for the Young,' * Music,' and taet but not I«út the ' Correspondence Columns.' If it were not invidioo.« lc ould poiut out three or four of your correspondeuts whose hands I should like to grasp aud thank them personally for their contributions, though it would perhaps bo something novel to them to have tbeii hand* grasped by the somewhat horny band.« of one of the sons of toil. If some oí my fellow working men, who spend their time and money шраЬисЬопзе;». would eoutrast oue number of 'ours with a twopeouy pot of beer,' I think they would at once acknowle-il&ro that they pay "too much for their whistle."

REPLIES TO QUEBIES.

*»* In their answers. Correspondents are respectfally requested to mention iu each instance the title and number of the query asked.

1Я934.]— ORGAN ACCORDION STAND.—I send two

sketches for tho benefit of "Sigmjinu," one. with *п instrument,the other without. Wiien the foot presses tbe

THE EYE AND THE TELESCOPE.

[288] Sir,—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, &c. 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 oue 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. Prestos.

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treadle down the instrument is caused to close; and when the foot is lifted the strong spring pulls the bellows out again by means of tho long lever fixed at the back. The diagrams oxplain tho rest.—Reed Tuxer.

[3W9-] —REPUBLIC OF QUAIANA—I am quite astonished at the remark of "J. Ö." I p. 499 к He eay* that I am mistaken in stating that the colonies ot Guian* are north of Venezuela. I never thought nor said that. I answered to the query about the" Republic** of Guiana, that I believed it was near Venezuela. I think even it is part of Venezuelan Guiana. I read in the Time» -«-шй weeks ago an article about a settlement in that country. I —bernardin.

[8949.] — GUAYANA OK GUAIANA. — Beside« the usual English error ul omitting the tiret A of this name, a letter quite essential to its sound in any regular orthoepy, "J. G." is very unlucky iu limiting the application о ( what is literally the most defined and naturaUy-fixed geographical name on any continent in the world. It has Iiiwbj-h applied to the whole riser island. or portion of South America that the Oronoco, by its unique bifurcation, detaches and isolates. Rising about the middle oí this vast tract, its tirst course is S. W. r.nd westward, directly/row the sea it is to reach; then, in the heart of the coutiuent, it splits into two, to the S.W. mJ N.W., oach equal in volume to the Rhine. The former called the Cassiquiare, or natural canal, after winding some 160 miles, enters the Ulo Negro (chief affluent of the Amazon) at about 1,500 milos from the sea. The other branch, the propor Oronoco, takes its mm course, northward, down various cataracts, and then eastward, till in ahont 1,000 miles it reaches the same ocean; and thus wo have the only rivor iu tho known world that, liko Adam's in Genesis, is "parted, and 1 lieu compasses a whole land. There are alluvial deltas, of course, but nowhere else is a tumi, a truo country, с oniprising mountain chains and all other elements of a с «uliucut, known to be thus moated with rivers and sea. Mow the three colonies, to which "J. G." eoutlues the илше, form not one quarter, and by far the worst quarter, o> I this vast and unique land of Guayana. The southern ..ill. or all that draius to the Amazon, is Brazilian, but Ijardly trodden as yet. More than a quarter, to the CS.W., formerly Spanish, is now Venezuelan, forming nbouthalf the area of that republic, and praised by ЖЧтпЬоШ as tho garden of the world. Its capital has aiot been moved, but very variously named, being the San 'Гоше and Nnova Guayana of old maps, afterwards Angostura, now lastly Ciudad bolivar. This quarter, equal in extent to France, all drains to the Oronoco. Tlio only low, moist, and uuhcalthy Guayana is tho remaining or maritime part, comprising the three poor ...loiiits "J. G." has alone mentioned, where the British, Dutch, and French have scratched but tho merest margins of low coast. It is remarkable the gold diggings discovered only three years ago in a high and cool table-laud of Venezuelan Guayana, had been heard of by Raleigh, and for'two centuries regarded us a fable. —E. L. G.

[4101.]—SUNDIAL— "W. H. C." will find a letter on page 464 Vol. X. of tho Enulish Mechanic, which may uelp him; also on pp. 520, 582, and 631 in tho same Vol., also on pp. 14 and 62 iu tho Vol. now issuing.—Current. [4161.]—REFRIGERATOR.—In answer to "Chico," ice is easily kept a week in tho hottest woathor by placing it in a large bag containing plenty of sawdust to • ovor and surround the ice, the bag bciug placed in a hole in the ground, in a cool spot, and boards borng placed over the hole, and old sacks over them. II the sacks are kept damp all the bettor. I alwaye keep ice t bus. the merchant sending it in a bag of sawdust; ш that alono, it often keeps a week.—Current.

14170.] -SMOKE BURNING.—There is an articlo en iiie above subject, p. 875, Vol. X.—Sehoius.

[4172.J — BORING BAR.—You must construct some sort of woodou frame to support your bar, and if yon take only a small cut at a time no very great rigidity is required. I should take three cuts through a pair of brasses, and tho last cut not more than l-5Uin. all round. 1 f you take care to level tho work flret with tho epiritlevel you can at any moment make sure of your bar, оно way at least, by the same means, which may save much time iu tho event of a cutter sticking and breaking, or if you think the supports may have given way и little by'an over strain. 1 ouee bored a 5in. hole in a barrel-holding head-stock of a rifling bench thus:—I first fitted ou two blocks of hard wood, with a tenon below to go between the sides of the bod, and a bedstead bolt or bedscrew to eaeh to hold it down. I then mado a cutter exactly liko the shifting sido of a Franklin's expanding centre-bit—viz., with the shaving half of the ordinary carpenter's oentro-blt, armed with a nicker on its outside edge, Bud fitted it to the j bar that 1 had previously used for tho small holes in tho other head of tho machine. With this new cutter, and the bar and heads used before, I bored holes for taking a 2' bar through the block moutionod above. The cutter for the 5in. bolo was made of a piece of flat bar-steel, drawn out uarrow at one end, and hooked a bit, so as to be like a roughing-out turning tool 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, ehippod ovor the tail of tho carrier, formed a lever. On the othor ond,of tho bar another carrier and an old dog chain with a swivol <ju it, hung over a pulley ноше distance off ,with a weight attached, gave the feed. It happened to be at the coldest time of a very cold winter, or I should have been knocked up probably. Of courso if you can fit up an old pedestal or two, and run iu some type metal or Babbit's metal bearings (or even lead) round tho bar, which has previously been wedged up to its right place, so much the better; 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 timo almost boyond computation—million* of years certainly.—Augustus.

IU9D.]—EMIGRATION TO THE WEST INDIES.— Two things aro to be borno in mind—1, that in tho «lobe's warmer half, viz., In latitudes below 80 , uo wood clearing (which is the llrst essential) nor any outdoor manual labour can be performed by Europeans, except at elevations above 8,UOOft., or at least li.uOOft.; 2, that nature has not, iu the tropics, made the exploitation of a labouring class, however poor—and least of all when they are frood slaves or their descendants—by a richer directing class, possible as ehe has here. Now, of the British West Indies (though nearly all arc hillior than the summit of Scotland), none contain ground 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 "tempuranco" men, going there young, might, besides their necessaries, raise coffee, and perhaps cotton; but no other of tho present etaple exports, which require lower and hotter ground. Innumerable wild products of both the high und lowlands, as hard fancy woods, dye stuffs, proserved fruits, oils, and other medicines, ought to be exportod; but the miserablo social state induced by two centuries

of slavery, scorns to have permanently banished civilized industry. The island nearly throughout is of wondroiiB, perhaps matchless, fertility and beauty; but seems 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, bv 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 mmtrahit wood 20ft. ¿«!h—and it must now or shortly differ little in social and physical state from a bit of central Africa, save in tho negroes having countless herds of half-wild swine, and being under Baptist fettoh-men, instoad of Obeah ones.—E. L. G.

[4196.] — CEMENT.—"A New Subscriber" will probably Und n cement made of resin and beeswax, coloured with Venetian red, answer his purpose. Say about 2oz. of resin, loi, beeswax, and about loz. 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 the following suit him :—1. Mix a pint of vinegar and a pint of milk; when fully mixed, clear it of the lumps, and let it settle; then sift into the liquid somo 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 also English Mechanic, Vol X., pp. 187, 391, 417, 4(52, 518, Û40, aud ШШ.—Current.

[4226.]—DOUBLE STOCKS.-I quite agree with "Norma " (although only an amateur too) that the host 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 the seed from those with flvo, 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 Broinpton Stock. I never saw more than four petals on a pip of the single-flowered annual Dwarf or Ten Weeks' Stock.—W. E. Cokdon.

[4340.] -FROM N. G. LAMBORNE.—N. G. Lamborno's velocipede was a four-wheeler, with the ordinary crank motion, drivon by tho hind wheels, 8ft. diameter; front wheels, 2ft. diameter; crank, 6{in.; swinging treadles, Oin. joint at crank, and 4in. joint which holds the treadle to the frame uear the front whcols; frame Sift, long, extreme breadth 22in.,driven by the vertical tread of the foot; seat over tho crank, and so high that the foot would just fairly reach the treadle when at its hunt downwards. It is a mistako in placing the seat far away from the driving wheel, and is a proof of bad management in placing the seat and treadles. I do not ndviso any one to inako after this plan, although it is the best that I have seen, except an invention that is now nursing. —N. G. Lamboiink.

eemi

[4417.] -SAFETY-VALVE FOR KITCHEN BOILERS, —lu answer to " Osmond Dobroe," a very good article was brought out some time ago (by Mr. Fletcher, Engineer of tho Manchester Association for the Prevention of Household Boiler Explosions',, which ls.eaid to bo unaffected by changes in the temperature. They arc made, I believe, for 10s. each, and cost about 10s. more for fixing, if tho boiler is in nee. It was illustrated and explained, as every other good thing is, iu this Journal, in the fifth Volume (p. 891, issued August 16, 1867).—

CURRENT.

[4418.1—SILVER COIN.—A Roman Family Denarius; Family Antonia, read ANT. AUG. III. VIR. R.P.C., rev. LEG IV. I find it quoted in оно of MM. Lincoln s catalogues, 2s. aud 8s., according to proeervatlou. Plated varieties are existing.—Bernaudin.

[4121.]-MAKING FLANNEL ADHERR TO BRASS. —One part Venice turpentine to four parts glue, thoroughly mixed, is the best I havo tried to make any. thing adhere to braes.—J. H. P.

¿4448] TRUE MERIDIAN.—A "Young Surveyor" 1 find that the best way to obtain tho astronomical meridian in (ftp field Is by compass, allowing for the variation of the needle, which in 1869 at Greenwich was 20: 4' wosterly. The difference between this valne aud that for I860 is about 50- (now probably about 1 ). This will not of courso apply to auy other part of England, but the reply to query (August 6 p 477) contains the results of determinations in 1868-9. Practical treatises on navigation give the method of finding tho magnetic variation, from which, as just stated, the true meridian is easily found. FW the determination of & fixed meridian line refer top. 2So, Jnnn in renlv to nnerv 2558, Sundial.—W . R. Bikt.

[4368.1—LINING-OUT SHAFTING.—Cnt circle (exact) of wood, to fit the bottom brass of each pedestal, and mark on the fiat upper side of the wood the exact centre. Set up your pedestals with the wood in, and strain a fine string from one ond to the other, to indicate the centro liuo. Lovel 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 the shaft will be put ш its placo before finally tightening the base bolts.—J. K. P.

[4408]—INDIA-RUBBER is the inspissated juice of several trees belonging principally to the following botanical orders ¡—Spurge ordor, or EuphorUaceie; fig and mulberry order; dogbane order, or Apocynra-, A complete list of names might be too long, but I beg to quote a few:- (я) Spurgo order: Euphorbia antiauorum, nereifolia, 4c, of the East Indies (Soesoeraof the Malay), Siphonia elástica, 4c, of Brazils, 4c. No) Fig and mulberry order: Ficus clástica, or Assam India-rubber; i. i mi ¡¿a, or banyan tree; F. religiosa; Castilloaeleulica; all from the East Indies. F. Brassii, V, esteru Africa ; t. macrophnlla, of New South Wales and Queensland ; F elliptica, radula, prinoidci, 4c, of South America, (c) Dogbane order: frceola elástica, of Sumatra ; Calatmu gigantea, the well-known Ycrcum-nar, or jungle plant ol the East Indies; fV'damio, end several other lianes of the Gabon; Willuabea eilulis, Luti Am, of Bengal, 4c. Many trees of tho Sapodilla order or Bapotacca-j yield also a milkv juice analogous to gutta-percha. I have given (No. MO, p- 272 of our English Mechanic) a note on Balata and Mussaraudnba.—Hebnardin.

[4113.] FEED-WATEB 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 being admitted into tho heater; I do not call it a heater, as my water is reaUy heated in the exhanst pipe as it leaves the cylinder. My exhaust pipe is 3in. diameter; the pipe from cold water pump travels horizontally for a few feet before entering exhaust pipe, both lying horizontally, so that tho water shall not bump in all a«, once but trickle, аз it were, out of tho pipe into exhaust nearly tho whole of tho revolution. Now to satisfy myself thisweek I took off tho head of the heater 12ft. from whoro 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 when the greatest rash of water occurred, so much that the Bteam returned at that particular point with considerable noise; that point can bo seen with steam at 401b. in the puffs as they leave tho pipe for the open air. Again I cangct no loud and clear bark from the exhaust when pumping as I can when the wator ie 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 Í blew into a close cask of 120 gallons. Then I had twice as much silex deposited on its sides as I do now 1 have replaced it with an Iron one as being more orthodox; I presume the reason is because tho wood is the bost non-conductor of heat.—One Eye.

[4416.]—PHOTOGRATHICAL.—If "John "is thefortunate possessor of the fourth Volume of the EnoLisii Mechanic, he wiU find all he requires, I think, in the exceedingly good chapters on " EW"tar^botography," by "A.H. W„" on pp. 25, 41, 89, 110, 201, 2o0, and 285 in that Volume.—Сившгкт.

Juno 10, reply to qncry 2558, Sundial.

[44611— SCREW CÜTTINO.—I am not sure that onto is a dictionary word. Perhaps your compositor has done rightly iu altering it to tnio in. my letter, on paue 525, but he' has spoilt my meaning, while improving my grammar. I remember tho samo 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 frosh distilled benzine, and it may be used without causing tho ink to ran. When dry, the paper resumes Its opacity. (See English Mechanic, Vol. X., p. 35; also Vol. IX., p. 897.)—Current.

U4Ô7 and 4551.1— IMPRESSIONS FROM PRINTS ANDTRANSFERRING ENGRAVINGS TOWOOI).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 tho vaponr of iodino for about flvo minutes, then applied to the preparod sheet of paper, and the two pressed together for a minute or two in a copying prose. The iodino is said to fix itself on every part of the engraving covered by printing ink; such being the case, the remainder of the process becomes evident. I imagino it would bo equally appUoable to wood. Not proved.—T. W. Boord.

[4472.1-SOLDERING BRITANNIA METAL.-" J. B—_r" will And a method of soldering any kind of metal without fire, described on p. 525, Vol. X.— SKRGirs.

[4473 1—INTENSITY COIL.—I send a rough diagram of a machine made for winding fine wire on to coils From the following description, " B. F. D. '"»У be able to construct one for his own use A is a rod "tat c»n bo taken off the uprights upon which the coil is fixed, С is a wooden rod to carry tie reel that contains the wire; В 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, aud which can bo turned upon its own axis At В is a stud that screws on to the bar inside the tube, which moves in either direction when

[graphic]

the handle is turned; it also has a small hole in it for the wire to равв through on to the coil at A. It will be seen that when the coll is turned by moans of A, it draws tho wire from the reel C, through В winch can be brought opposite to any part of the coil. I have made largo coUe on this machine, and have found but little trouble in winding the wire on to them. Tho handle on В would be 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 tho oore and primary coil diminishes as the square of the distance ; therefore, what is gained by insulation is partly lost through the space itoccupios; an insulator should, therefore, be used that takes up the smallest space. I think " R. F. D." haB not insulated his coil any too well.—J. T.

[4474]—HORSE POWEB.—The common rale for calculating the power of a eteam-engüie is '7854 d*p n 550-horsepower, or i|ip> = 700-horse power—(<i). But as the steam should be stopped off at \ the stroke .-. <r- p v = 983-horse power. This is the simplost general expression; but as a commercial expression, л r> can be assumed = SO x 81 = 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

Ьате by division d> - 10 H. P. .-. H. P. = 'jj = u°minal power of non-condensing steam-engines. And sttbstitnting71b. per square inch instead of p ш equation^)

d and v remaining as before, wo find I '• ■ ¡" nominal power of condensing engines. For the aotual power of steam-engines, equation (a) muat be applied in all cases with properly reduced values ol 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

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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.

(4519.]—PHOTOGRAPHY.—Procure some good benzoin, place it in a plate nn.l apply moderate heat until it in quite fluid, pour it into a cold plato und when quite, col'i it may be broken in pieces. Then dissolve luz. of tbo fused benzoin in Hot. of methrbti-d alcohol mid 20 ßraüis oí suudarac. Then add 20 drop* of mastic varuleh, made bv melting gum mastic und adding turpentine t.« it whilst iu A fluid state. The impurities will ьосч settle, and it is ready for use. Should the varnbh he too thick add more spirit.—H. J. Kinohau.

[4520.]— PERCH FISHING.—I think the best time to fish for perch is from September to January in large deep eddies and ponds by the side of a river. There are numbers oí these iu the Thames, and excellent perch fishing ы to be found near the paper mills at Temple. ncorMarlow. Weira are the best places in summer tiuie, but perch are not in first-rate condition then. Thero are several methods of fishing for them, and oí course different kiude of tackle. I think the must ¿ucceseíttliulhe. Thames is the method known as *• paterno^teriug." Attach a lead to the end of a gut hue about 4ft. orSft. bug, and about 3in. and lain, above it two tihórt pieces ul gut, about -Ain. or 5iu. long, with No. H or 9 hooks fastened so as to stand uut at right angles. Bait with a live minnow or gudgeon—the hook put through the upper lip. A longish rod, with a free-running line, I have always found the best. 1 prefer the plaited silk lines myself, ав those made of silk and hair " kink frequently and are very apt to hitch instead of running free; besides, they are not so strong as the plaited silk. When all is prepared, with the lead hanging 6ft. or 7ft. from the top of the rod, drop the Une gently into the water till the lead rests on the bottom. Shift the bait every now and then; don't strike directly you feel a twitch,but "bide a woe," and when you feel a second attack tighten the line, and give я sort of "lift," as the perch is rather ft delicate-mouthed fish, and if you "strike" hard you are apt to hw; both fish and bait. Perch generally" swim in shoals, но if you succeed in lauding one keep to the same place. There is another method of Ashing for perch, which consists in baiting with brandlings, and using either ordinary tackle or the Nottingham style. A few broken worms thrown in now und then will often attract the fish. In these methods I let the float be carried well under before striking.—A. T., Staines.

[-1521.]—EXTRACTING HONEY FROM THE COMB.

Jot the comb iu pieces with a sharp knife so as to

divide all the cells, and place the pieces in a colander overa basin or jar to receive the honey as it drains off.—

T. W. ÜOOKD.

[4522.]— PURE CHARCOAL.—I am rather puzzled by Mr. Ibbotson's quory. Does he mean what we, as chemists, call puro charcoal, or what druggists sell as such—a verv serious difference? Pure carbon is almost impossible to obtain, except in the form of the diamond, hut a "pur« vegetable charcoal" is made by carbonizing willow or other wood iu an iron retort. I imagino *L What kind of fire and hot pinte is pure ?" must refer tu this. For such ft purpose, with an írou retort fitted with au exit sufficient only to give vent to the gases, any fire will do, but the purest fire in ordinary use is a spirit lamp. For small quantities a piece of gas-pipe, plugged at one end and partially closed at the other, would serve. N.B.—The *' purity *' of the charcoal is a superstition, and has nothing to do with the effects.—SшMa.

[4531.]—STEAM JOINT.—" Schemer " will overcome the difficulty ho has experienced in obtaining a perfectly tight joint by having a joint made exactly like a universal swivel oí a gas bracket. He can bring the boiler nearer to the engine, or vice vena, by a telescopic joint made secure by a stuffing-box.—D. Clarxs.

[4528.]—CARVING AND TURNING SOFT WOOD.— For external surfaces use the gouge and chisel. The insides of boxes, &c, arc shaped and finished with what Ате called hook-tools; their form varios with tho taste and requirements of the operator, and considerable practice is necessary to uso them properly. The screws лго cut with a rough kind of traversing mandril. The tools used for carving are small gouges, chisels, Ac., of various shapes and sizes.—T. W. Bookd.

[4639.]— 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" ef the microscope, midway between its extremities, and also between the p.illeys. "S." will easily comprehend its working from tins briof description. If not, let him devise the workin 4 of a ship's rudder by the "wheel "— tho principle* are the same. As regards its accuracy: I will focas a 1-12" with it, and do nightly uso an ¿' without difficulty. So far as foe wising is çpneernod, the Япе movement may be dispensed with where the cbaiu movement is used, but tho fine movement, if well made, useful for microinctrical purposes, and should Always be applied where expense is not of vital importance.— H. P.

[4539.]—CHIMNEY.—If you build a chimney for four large boilers and determine to have a gooJ draught, ehooso any form—round or octagon is the best—let it be 40 to 50 yards high, 5 yards iu diameter at the bottom, And parallel iimide, most decidedly, all the way to the top,— WAHsaor.

[4540.]— MOUNTING PLANE MIRROR IN REFLECTING TELESCOPE.—Mr. A. White's plan would * 'nHerBcüel shifted tho optical axis of his telescope parallel to the tube, and so brought it close to the side. Mr. White shifts his angularly within tho tube, which will havo no other optical effect than he could get by aUfting the tube with tho mirror. If he will cousidor his picture he will seo that, without some as yet unknown virtue in the tube itself to force tho mirror only to show objects towards which the tube ia directed, he would only see just such objects as lie in the direction of the axis of the mirror; and verv little of them, since ¿10 gets tho tube (the lower half iu'hie figure) iu the way, and only the extreme upper edge of his mirror (us fthown In the figure) would be available to form an imago.— К. А. Pkoctor.

[4543.]— TORTOISE-SHELL COMBS.—The edges of the fracture should be scraped smooth, so as to overhip each other, and freed from grease, then dipped into hot water t<> soften them, pressed together with hot tongs, and li-tlv, plunged into cold witter till hard

Again,—T. W. B'JORD.

[454Л] -LATHE, Ac—TO " BIERLALA."—If you aro limited to three rows of divisions, I think 180, 9o, 84, are perhaps the best. I am strongly in favour of a row containing 11,13, 17; also li) and 14, if your diameter is sufficiently great, else the 6th and 7tb of tho 17 row come too close to the 9th and 10th of tho 19 row, unless your holes иго extremely small. Less than 7in. diameter will scarcely hvld them. I have this very day done the fitting of my new donble bearing mandril, and got tho 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 toftry it—tingle-handed I mean, of course. My hardened fast-collars are coned with tho slide rest set 1' taper for the inside of collar, and £deg. or ttOiuin. taper for the outside of collar and the inside ot cast-iron fitting. I do not shrink the collars in by heating tho 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, uuless indeed you put n good stout prop in to support the train. Your " 35-" in the last line appears to be a misprint. The lootc collars fit tight on to the cylindrical portions of the mandril, and are adjusted by scrow nuts. I do not intend to have the work japanned, ns I have heard of collars being tempered or losing some of their hardness through excess of heat employed. Miue are as hard as I could make them, and not tempered at all,—J. K. P.

[4546.] —DIVISION PLATE.—The numbers of the division plate which I find most useful are

720 360 200 144 120 119 96 divide into differences 3 Д » » д о со , (I may add that Edwiu Baker, of 14, Mount-row, Berkeley-square, London, issues a list gratis of the '• Ready Reckoner for the Dividing Plate ;") but there are also found useful for soino amateurs who do very line work these numbers, say—

180 136

divide into differences °* **

d Holtzapffel's lathes, to some of them were put

these individual numbers, 221, 209, for very fino rings or
flutes, when you use them all. The other parts I cau-
uot 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 littlo discussed; if true, as it
most likely is, it is au illustration of "natural selec-
tion," and its cognato doctrines, ehowlng how natural
species are formed and modified by surrounding condi-
tions.— Sigma.

[4547.]—A FIELD OF BARLEY GROWN FROM OATS.—" S. G." will find, in the "Vestiges of the Natural History of Creation " (see p. 144, Ed. 8,1950;, the following much earlier mention of this subject:—" It is now fully ascertained that tho various bread-forming grains, whoat, barloy, oats, rye, are resolvable into one. If wheut be sown in Juno, and mown down so as not to be allowed to come to ear till the next eeason, the produet will bo found to consist partly of rye or some other of tbe cereals. Oats have in like manner been transformed into rye, barley, and even wheat. Till a recent period, this phenomenon was doubted; but it has been tested by experiment, and reported on by so many credible persans, that it can no longer bo rejected. And it appears that poorness of soil ans the same effect as mowing down. One obscrvor states that, in a field of wheat, near Lucerne, he saw ears resembling barley, but with grains similar to rye, growing from the same stem with ears of wheat." The author refers to the Gardener*4 Chronicle, 1846, pp. 118,102, and August and September, 1844; also Mag. Sat. Hut. new series, i. 574; and ltep. Roy. Soe., ÍS46, p. 881.—W. P.

[4548.]—IMMERSION LENSES.—These lenses possess the great advantages of being easy to work, and of possessing greater "penetration" than a "dry" lens. Their price will vary from £3 for a German 1-lGin. to £50 for an English l-50in. of first-class make. If "M. J. C." be ft young begiuuer, and is contemplating the purchase of an "immersion," let him take to heart PitnWt'* advice to persons about to be married—" Don't I" He will find an English Jin. answer all his requirements for some year». If ho 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 lending makers would show him their working. An English Jin. may be purchased for about £4, but I question the utility of applying the immersion principle to lenses of these long foci.—ВТ. P.

[4552.]— AVIARY.—Tho beat time for purchasing birds to keep in an aviary is tho fall of the year, now rapidly approaching. This of course applies to such birds as the bullfinch, chaffinch, linnet, greenfinch, reed-sparrow, yellowhammer, Ac, which are more likely to live when taken in the antumn. 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 more 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, but its notes are inferior, although it sings from the early morning to the late evening. It Is very hardy and often lives eight years in a cage. Tho linnet, of our field birds, 'is perhaps tho 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 have either young or eggs at that season.—S. G.

[4554.]—PENDULUM.—Your correspondent "Vibrator" has discovered a "mare's nest." He wishes to know " why a clock should gain time by raising the bob, as by the law a longer swing should be accomplished in the same time as a shorter one ?" the law being, as he says, that a weight suspended by a silken cord will move in unequal spaces in equal times. In ко taras the law ol pendulum motion, he is vin л sense correct, although .stated in auch a comaiou-ilice manner. Yet ho fails to

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

[4554.1—THE PENDULUM.—"Vibrator" is in error respecting the pendulum. The following are among the laws of the instrument:—1. At the same station, pendulums оГ tho same length move through cucloidal arcet whether long or short, in the same time. Common pendulums, which oscillate in circular arcs, practically possess this property when their arcs do not exceed 5-1 or 6. 2. The times of oscillation of pendulums of different length*, vary as the square roots oí this bmgth. Tims, if at the same station, one pendulum be four times the length of another, it will take twice as much time to make itsoscillatiou; if nine times the length, thrice tbe timo; 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 pendulums.—W. P.

[45Ö3.]—BRASS COIN,—This Is a jetton or counter of the time of Quoen Anne. They were used for calculating. Tho word "jetton" is derived from the French verb jctter, to throw or cast; hence to Comí up an account.—T. W. lioonn. ê

[4567-] — MATHEMATICAL INSTRUMENTS. — Broken instruments aro hardly worth repair. Tho ph tí s 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 shope. A friend of mine bought a eplendi d set some time since for 80s., but there seems a prejudice against them. The pens are never so good as Ellio 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 tbreo kingdoms the county is situated in which he carries on his business; and as the law regarging the dealing iu second-hand goods, old metals, bones and rags, diffère so essentially in England, Ireland, and Scotland, and there are besides so inauy local acts in various towns, that it is almost, if not quite, impossible to give him a satisfactory reply. Wnen he writes again, giving his Joe кд, 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 and see the inspector or superintendent, and ask 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 tho courtesy (as I would) to show their authority for the restriction; and if there is enact, your correspondent on reading it can judge by his own common sense whether tho local guardians of the peace aud 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.l.

[4570.]—A LEGAL POINT.—In the 32ud and 83rd Vic, cap. 99, 'The Habitual Criminals Bill,' sec. 17, it is enacted :—" Any dealer iu old metals, as defined in tho Old Metal Deilers;Act, 1861, who sh ill either personally or by any servant or agent purchase, receive, or bargain for lead, whether new or old, in any quantity at one time 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, tobe recovered in the same manner as penalties incurred nnder 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.

QUERIES.

[4572,] —GEOLOGICAL.—Near Malvern are воте limostoie quarries. Can any of your numerous correspondents inform me to what formation they belong 7— Philosopher.

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

[4574.1— PARAFFINE OIL.—Can any brother roaderof the English Mechanic inform me if there is any mixture that can be added to inferior paraffine oil to cheapen and improve it for burning in lamps ?—А Роов M EC н An i с.

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

[4576.]— BLACK BRASSWORKOF 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 шану plans of construction that havo been recommended. "Inductorium" stated lately that the groatest 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. ЛУШ paper, soaked in paraffine, answer as well as gutta-percna tissuo tu insulate the lavera? and how much would be required/ But if "Sigma" would give a working description of what he considers the bent plan of coil to give a spark Sin. or 4in. with 4 Uuuseu's colls, he would oblige.—Operator . [457*.]— STRETCHING GUT-BAND.—Is there any wav of permanently stretching ft new gut-bund 2iu., wh'ichis about 3 vards long, au.l Hu. in diameter?— T. E.

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