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very-day electricity indeed, and hence their value lihtning preventors, not attractors. You can disre, silently and without shock, the largest electrical tery, by simply holding one pole while you present 18rp needle toward the other. In this way there is doubt every right lightning conductor helps in a to discharge the cloud silently, and prevents hes that would, without it, have occurred. But in excessive tension of storm electricity this purpose better served by delicate needle points than by accidental raggedness of any metal termination. ry experimenter knows this is the case even with an trical machine in good order. Doubtless there is a erence between the action of Messrs. Newall's atiful "attractors" and a broken bar end in sune, but not in a storm. If anything can be said to ract lightning it is the pointedness of the whole lding or rising ground. Spikes make no difference, knobs as big as any dome; and nothing can be more surd than carrying out conductors an inch above or onel what they are to protect. (The poor Duke of rk is spitted on the top of his column!)

1. Insulation is equally preposterous, as your second swerer perceives. It is abundantly proved the elec ical passage will never turn aside from the line of st conduction.

5. For his "taken deep enough into the ground," ad simply, "taken to the next metallic mass that is metal communication with the ground." As every odern English building has metal water-pipes from le ground up to the metal gutters," it is so far bsolutely protected already. Accordingly, I defy you > cite a case of damage by lightning in all England, this century, outside a building and below the level f its gutters. They are either on the outside, above Il gutters, or inside, by descending a chimney. No onductors to the ground then are ever wanted,-you have them already-bnt simply from chimney tops, or other "attractors," to the nearest gutters. Whatever netal then you see spent under colour of lightning protection, lower than the highest gutter level, is merely jobbed in for "percentage" by quacks, patentees, architects, et hoc genus omne, that the mighty wisdom of Mr. John Bull creates as his ornaments and oracles, his percentagers. I saw once a poor (not in benefice) parson, whose school-house was being lightning con. Auctored entirely comme il faut-pointed attractors of highest finish,-the insulators that F. Bedford would basely imitate with "bottle-necks," and all. Being a fine day, as they carefelly brought the work downwards, before connecting with the ground, it gave beautiful sparks, of course to the astonishment of his 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 convincing 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 see what all this is wanted for.

6. But though conduction is needed only to the gutters, please observe it is needed from every point 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; on Salisbury Cathedral, six. To know precisely the points needing protection, all you have to do is to imagine a model of your building, and that you have in your hand a circular plane, say, a tambourine, as large as it would stand upon. Whatever point 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. at least we 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 utterly wanton and inexcusable that such a thing as injury to a public building by lightning, in a 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. GARBETT.

So

THE SUN.

[279] SIR,-I wish to ask the author of the Almanac" is it stated that the sun is in the constellation "Astronomical Notes" on what page of the "Nautical Gemini on the 1st July, 1870. On the contrary, we find in that work, as well as in several others on astronomy, that the sun is stated to be in 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 because 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 that the sun was in the same constellation, because his R. ascension was found to be quite different? How otherwise, then, I ask can the "inference or conclusion" in question be anything G. FIRTH. but "illogical."

ares;

LUNAR MOTION.

[280] SIR,-I have received the ENGLISH MECHANIC 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 allusion 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 motion produces on the matter moved. It is known that matter moving round 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 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-spheroid will 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 bare, and no air or water could exist on the side of the moon turned to the earth.

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

Toronto.

EXPOSURE OF PLATES.

[282] SIR,-In answer to "E. T.'s" question, asked to a curious discovery recently made by M. Bazin. some weeks since, allow me to call his attention 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 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 simultaneously 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 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 be 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 has tried other colours, but finds red to be the only one which gives satisfactory results.

J. W.

APPROXIMATELY RECTIFYING THE CIRCLE.

[283] SIR,-I was rather surprised when I learned from "E. L. G.'s" letter (250) that the ratio had been twice wrongly quoted in my letter, as respects the sixth decimal figure; because among other items of perfectly useless knowledge, I include my remembrance of the values of , e, 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 the 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 solution; 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, But I have never more or less directly, the value of . made use any approximation to the natural value of the ratio, except-in very rough work-the oldfashioned fraction In all other cases the loga

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 B revolved round the same centre, and had no rotation round its own centre C, the rithm of has alone been of service to me. inatter, which would be moved on B, by centrifugal

A

B

force, would not pass ontward in all directions from its centre C, but pass backward from the centre of motion at D, over all parts of B, as shown by the small curved arrows; and it will be further observed that all the matter on B moves in the same direction at the same time, which is not the case with it.

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

THE OLD HUNDREDTH IN HAWKINS' NOTA- sky?" I never supposed a cloudless sky; I endeavoured to

TION.

[278] SIR,-Your "Harmonions 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 whole of the 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 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 arrangement 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 lending note of the third strain in all the four harmonized parts should be omitted.

S. D.

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 and 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 out of ten, had occurred one out of ten in 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 a discharge of artillery would 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 30 miles would be more beneficial than "Lex's" tank-water. I think, after a few more dry summers, something will be done, unless in again to prevent it. steps

the "law"

R. P.

22 7'

RICHD. 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 "Littus Habet Conchas," is one not in any 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 Habet Conchas," does not allude to any published works as records of observations and deductions. So far from identifiobservations, but simply as the results of his own cation 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 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 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 illegi bility is necessary or favoured in commercial circles, I flatly deny, whatever may be the presumed rapidity of thought thereon attendant.

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VULCANIZING INDIA-RUBBER.

[286] SIR, Several of "our" correspondents have recently asked for information about vulcanizing indiarubber-whether it can be "re-worked," how it is made, and sundry other matters in connection with this subject. Premising that the various processes are still 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, 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 fire, turned black, and became hard and horny. The method now practised is to mix caoutchouc with from 2 to 10 per cent. of sulphur, and submit it to a temperature of 270° to 300° Fahr. A higher degree of heat 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 250 Fahr., and immerse in it the caoutchouc, previously rolled into rough sheets or cut to any convenient form or size, and atlow 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 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 1846:-"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, fitting, or moulding such compounds. in, or upon such moulds or forms, 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 "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 unalterability by climate or artificial heat or cold; impermeability to air, gases, and liquids; facility of being ornamented by gilding, painting, &c.; insolubility and durability.

The process patented by Mr. Burke consists in the use 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 is afterwards subjected to a heat of from 250° to 280° 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 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 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. H. U.

CONTRIBUTORS AND QUERISTS. [287]-SIR,-"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 one 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." 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 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 no single reader the title to demand as 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 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 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 such 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 pages 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.

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 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. think this plan has only to be tried for the comfort of it to be appreciated. S. T. PRESTON.

I

A VALUABLE TABLE.-The following table will be found valuable to many of our readers :-A box 24in. by 16in. square, and 28in. deep, will contain a barrel. A box 26in. by 15 in. square, and 8in. deep, will contain a bushel. A box 12in. by 11 in. square, and 9in. deep, will 8in. deep. will contain a peck. A box 8in. by 8in. square, contain half a bushel. A box 8in. by 8in. square, and 4in. deep, will contain one gallon. A box 7in. by Sin. square, and 4in. deep, will contain half a gallon. A box 4in. by 4in. square, and 44in. deep, will contain a pint.

EXTRACTS FROM CORRESPONDERE

A WORKMAN'S TESTIMONY.

Brunswick-road, Sheffield, says:-1 for some time to express my approbati add any testimony to its value. Be tone of some of your recent y spondents.' I have subscribed t periodicals for about twenty yea such satisfaction from one befon : many points of interest contains the rest being the articles on Che Science for the Young, Music, the Correspondence Columns. I Ic ould point out three or four of y whose hands I should like to grant perhaps be something novel to the personally for their contributions, y hands grasped by the somewhat hard of the sons of toil. If some of m men, who spend their time and money: would contrast one number of outs pot of beer,' I think they would at that they pay "too much for their whistl

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treadle down the instrument is caused to close; a when the foot is lifted the strong spring pulls the bello out again by means of the long lever fixed at the back The diagrams explain the rest.-REED TUNER,

[3949.]-REPUBLIC OF GUAIANA.-I am quite a tonished at the remark of "J. G." (p. 499). He say that I am mistaken in stating that the colonies of Guias are north of Venezuela. I never thought nor said that that I believed it was near Venezuela. I answered to the query about the "Republic" of Guiana I think even i

is part of Venezuelan Guiana. I read in the Times some weeks ago an article about a settlement in that country -BERNARDIN.

of slavery, seems to have permanently banished
civilized industry. The island nearly throughout is of
wondrous, 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, 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 impene-
trable wood 20ft. high-and it must now or shortly differ
little in social and physical state from a bit of central
Africa, save in the 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 pro-
bably find a cement made of resin and beeswax, coloured
with Venetian red, answer his purpose. Say about 2oz.
of resin, oz. beeswax, and about oz. Venetian red.
Melt it gently and stir it well together; and make both
the bottle and brass cap hot before applying the cement.
-AUGUSTUS.

[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 are made, I believe, for 10s. each, and cost about 10s. more for fixing, 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).CURRENT.

Family Antonia, read ANT. AUG. III. VIR. R.P.C., rev. [4418.]-SILVER COIN.-A Roman Family Denarius; LEG. IV. I find it quoted in one of MM. Lincoln's catalogues, 2s. and 3s., according to preservation. Plated varieties are existing.-BERNARDIN.

[4421.]-MAKING FLANNEL ADHERE TO BRASS. -One part Venice turpentine to four parts glue, thoroughly mixed, is the best I have tried to make any thing adhere to brass.-J. H. P.

49. GUAYANA OR GUAIANA. Besides the 1 English error of omitting the first A of this name, tter quite essential to its sound in any regular Oepy, J. G." is very unlucky in limiting the applion of what is literally the most defined and natu-fixed geographical name on any continent in the id. It has always applied to the whole river island, ortion of South America that the Oronoco, by its que bifurcation, detaches and isolates. Rising about middle of this vast tract, its first course is S. W. and Award, directly from the sea it is to reach; then, in beart of the continent, it splits into two, to the S.W. N. W., each equal in volume to the Rhine. The er called the Cassiquiare, or natural canal, after dling some 150 miles, enters the Rio Negro (chief zent of the Amazon) at about 1,500 miles from the The other branch, the proper Oronoco, takes its a course, northward, down various cataracts, and then ward, till in about 1,000 miles it reaches the same san; and thus we have the only river in the known rld that, like Adam's in Genesis, is "parted," and ncompasses a whole land. There are alluvial deltas, course, but nowhere else is a land, a true country, prising mountain chains and all other elements of a atinent, known to be thus moated with rivers and sea. w the three colonies, to which "J. G." confines the ine, form not one quarter, and by far the worst quarter, this vast and unique land of Guayana. The southern .1f, or all that drains to the Amazon, is Brazilian, but rdly trodden as yet. More than a quarter, to the W., formerly Spanish, is now Venezuelan, forming out half the area of that republic, and praised by umboldt as the garden of the world." Its capital has [4226.]-DOUBLE STOCKS.-I quite agree with ot been moved, but very variously named, being the San "Norma " (although only an amateur too) that the best omé and Nueva Guayana of old maps, afterwards plan to save seed to raise double stocks from is to dengostura, now lastly Ciudad Bolivar. This quarter, stroy all flower pips on single flowering plants that have qual in extent to France, all drains to the Oronoco. only four petals, and to save the seed from those with he only low, moist, and unhealthy Guayana is the re-five, six, or seven petals: the more petals, the better the aining or maritime part, comprising the three poor seed, although I never saw a pip with more than seven olonies "J. G." has alone mentioned, where the petals bear seed, and then only on the Giant or Bromp3ritish, Dutch, and French have scratched but the ton Stock. I never saw more than four petals on a pip nerest margins of low coast. It is remarkable the gold of the single-flowered annual Dwarf or Ten Weeks'-J. K. P. 1iggings discovered only three years ago in a high and Stock.-W. E. CORDON. Cool table-land of Venezuelan Guayana, had been heard of by Raleigh, and for two centuries regarded as a fable.

E. L. G.

[4131.]-SUNDIAL.-W. H. C." will find a letter on Dage 460, Vol. X. of the ENGLISH MECHANIC, which may thelp him; also on pp. 526, 582, and 634 in the same Vol., also on pp. 14 and 62 in the Vol. now issuing.-CURRENT. [4161.3-REFRIGERATOR.-In answer to "Chico," ice is easily kept a week in the hottest weather by

placing it in a large bag containing plenty of sawdust to Cover and surround the ice, the bag being placed in a hole in the ground, in a cool spot, and boards being placed over the hole, and old sacks over them. If the Sacks are kept damp all the better. I always keep ice

thus, the merchant sending it in a bag of sawdust; in that alone, it often keeps a week.-CURRENT.

[4170.]-SMOKE BURNING.-There is an article on the above subject, p. 875, Vol. X.-SERGIUS.

[4172.]-BORING BAR.-You must construct some

sort 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 brasses, and the last cut not more than 1-50in. all round. If you take care to level the work first with the spiritlevel you can at any moment make sure of your bar, one way at least, by the same means, which may save much time in the event of a cutter sticking and breaking, or if you think the supports may have given way a little by an over strain. I once bored a 5in. hole in a barrel-holding head-stock of a rifling bench thus:-I first fitted on two blocks of hard wood, with a tenon below to go between the sides of the bed, and a bedstead bolt or bedscrew to each to hold it down. I then made a cutter exactly like the shifting side of a Franklin's expanding centre-bit-viz., with the shaving half of the ordinary carpenter's centre-bit, armed with a nicker on its outside edge, and fitted it to the bar that I had previously used for the small holes in the other head of the machine. With this new cutter, and the bar and heads used before, I bored holes for taking a 2" bar through the block mentioned above. The cutter for the 5in. hole was made of a piece of flat bar-steel, drawn out narrow 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, shipped over the tail of the carrier, formed a lever. On the other end of the bar another carrier and an old dog chain with a swivel on it, hung over a pulley some 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 course if you can fit up an old pedestal or two, and run in some type metal or Babbit's metal bearings (or even lead) round the 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.

following suit him:-1. Mix a pint of vinegar and a
[4196.]-CEMENT.-"New Subscriber" will find the
pint of milk; when fully mixed, clear it of the lumps,
and let it settle; then sift into the liquid some quick-
lime, 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. See
513, 640, and 660.-CURRENT.
also ENGLISH MECHANIC, Vol X., pp. 187, 391, 417, 462,

velocipede was a four-wheeler, with the ordinary crank
[4340.]-FROM N. G. LAMBORNE.-N. G. Lamborne's
motion, driven by the hind wheels, 8ft. diameter; front
wheels, 2ft. diameter; crank, 64in.; swinging treadles, 6in.
joint at crank, and 4in. joint which holds the treadle to
the frame near the front wheels; frame 5ft. long, ex-
treme breadth 22in., driven by the vertical tread of the
foot; seat 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 placing the seat far away
from the driving wheel, and is a proof of bad manage-
ment 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. LAMBORNE.

[4448.] TRUE MERIDIAN.-A "Young Surveyor" meridian in the field is by compass, allowing for the will find that the best way to obtain the astronomical variation of the needle, which in 1869 at Greenwich was 20° 4' westerly. The difference between this value and that for 1860 is about 50 (now probably about 1). This will not of course apply to any other part of England, 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 meridian is easily found. For stated, the true the determination of a fixed meridian line refer to p. 285, June 10, reply to query 2558, Sundial.-W. R. BIRT.

[4461.]-SCREW CUTTING.-I am not sure that onto 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 my meaning, while improving my grammar. I remember the same thing once before.

[4465.]-TRACING PAPER.-"H. U." may make any with pure and fresh distilled benzine, and it may be drawing or writing paper transparent by damping it used without causing the ink to run. When dry, the paper resumes its opacity. (See ENGLISH MECHANIC, Vol. X., p. 35; also Vol. IX., p. 397.)-CURRENT.

AND TRANSFERRING ENGRAVINGS TO WOOD.[4467 and 4551.]-IMPRESSIONS FROM PRINTS 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 the 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 every part of the engraving covered by printing ink; such being the case, the remainder of the process becomes evident. I imagine it would be equally applicable to wood. Not proved.-T. W. BOORD.

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

[4368.]-LINING-OUT SHAFTING.-Cut a semi-
circle (exact) of wood, to fit the bottom brass of each
pedestal, and mark on the 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 B-
indicate the centre 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 the shaft will be put in its
place 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 order, or Euphorbiacea; fig
and mulberry order; dogbane order, or Apocyned. A
complete list of names might be too long, but I beg to
quote a few:- (a) Spurge order: Euphorbia antiquorum,
nereifolia, &c., of the East Indies (Soesoera of the Malay),
Siphonia elastica, &c., of Brazils, &c. (b) Fig and mul-
berry order: Ficus elastica, or Assam India-rubber; F.
indica, or banyan tree; F. religiosa; Castilloa elastica;
all from the East Indies. F. Brassii, Western Africa; F.
macrophylla, of New South Wales and Queensland; F.
elliptica, radula, prinoides, &c., of South America. (c)
Dogbane order: Urceola elastica, of Sumatra; Calotropis
gigantea, the well-known Yercum-nar, or jungle plant of
the East Indies; N'dambo, and several other lianes of
the Gabon; Willugbea edulis, Luti Am, of Bengal, &c.
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 Massaranduba.-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 being admitted into the heater; I do not call it a heater, as my water is really heated in the exhaust 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 the water shall not bump in all at once but trickle, as it were, out of the pipe into exhaust [4174.]-GEOLOGY.-"Veritas's " question cannot be nearly the whole of the revolution. Now to satisfy myreplied to positively. It must be a time almost beyond self, thisweek I took off the head of the heater 12ft. from computation-millions of years certainly.-AUGUSTUS. where the water entered the exhaust pipe and watched [4190.]-EMIGRATION TO THE WEST INDIES.- the work of it with 101b. of steam, and instead of back Two things are to be borne in mind-1, that in the pressure I had a partial vacuum when the greatest rush globe's warmer half, viz., in latitudes below 30, no of water occurred, so much that the steam returned at wood clearing (which is the first essential) nor any outthat particular point with considerable noise; that point door manual labour can be performed by Europeans, can be seen with steam at 401b. in the puffs as they except at elevations above 8,000ft., or at least 6,000ft.; leave the pipe for the open air. Again I can get no loud 2, that nature has not, in the tropics, made the exploita- when the water is shut off, and I certainly think the enand clear bark from the exhaust when pumping as I can tion of a labouring class, however poor-and least of all when they are freed slaves or their descendants-by a gine works easier when pumping than not: but one richer directing class, possible as she has here. Now, point I do not understand, my exhaust pipe direct from of the British West Indies (though nearly all are hillier the cylinder is 12ft. long, and when I first tried it in than the summit of Scotland), none contain ground high 1863 I blew into a close cask of 120 gallons. Then I had enough for whites to work on, except the part of twice as much silex deposited on its sides as I do now I Jamaica east of Kingston. On these mountains, I be-dox; I presume the reason is because the wood is the have replaced it with an iron one as being more ortholieve that Englishmen, or at least "temperance best non-conductor of heat.-ONE EYE. going there young, might, besides their necessaries, raise coffee, and perhaps cotton; but no other of the present staple exports, which require lower and hotter ground. Innumerable wild products of both the high and lowlands, as hard fancy woods, dye stuffs, preserved fruits, oils, and other medicines, ought to be exported; but the miserable social state induced by two centuries

39 men,

[4416.]-PHOTOGRAPHICAL.-If "John" is the fortunate 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, 250, and 285 in that Volume.-CURRENT.

[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 which can be turned upon its own axis. At B 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 pass through on to the coil at A. It will be seen that when the coil 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 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 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, therefore, 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 steam-engine is 7854 d2 pv = the steam should be stopped off at the stroke... dep v 550-horse power, or d3 pv = 700-horse power-(a). But as = 933-horse power. This is the simplest general expression; but as a commercial expression, pv 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 pv we have by division d2 = 10 H. P. .. H. P. = d2 = nomi10 nal power of non-condensing steam-engines. And substituting 71b. per square inch instead of p in equation (a) da d and v remaining as before, we find H. P. = 32 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,

=

either from tables or otherwise. "Templeton's Engineers', Millwrights', and Machinists' Assistant," 4th edition, contains these tables, and much useful information for the practical man.-R. D.

[4474.]-HORSE POWER.-The following is a simple method of finding the horse power of a steam-engine. Square the diameter of the cylinder in inches, and divide the product by 12. The result will be the power with steam of 301b. to the square inch. From this, the power at any other pressure may be ascertained by simple proportion. For example: Required the power of an engine whose cylinder is 6in. diameter, supposing the steam pressure to be 40lb., 6 x 6 12 8 (horse power at 30lb. pressure). Then by proportion, 30: 40:: 3 : 4 (power at 40lb.)-VERTUMNUS. [4477.] The BOOKS. "Encyclopædia of Rural Sports," by Delabere P. Blaine, 8vo., 50s., 1852, and "Youatt on Dogs," 8vo., 6s., 1851, are both standard works. Mayhew, Richardson, and Jesse have also written on the same subjects.-CANIS.

[4478.]-BLUE INK.-1 Chinese blue, 2oz.; boiling water, 1 quart; oxalic acid, loz. Dissolve the blue in the 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. ENGLISH MECHANIC, Vol. X., p. 162).-CURRENT.

(See

[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 bottle, 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."-The 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. Since the mercury in the tube is almost continually ascending or descending, that in the vessel is

also constantly altering its level, sinking when that in the tube is rising, and vice versa. The adjusting screw may be made to work in a light brass frame attached to the vessel. The sketch will perhaps afford some idea of the position and arrangement of the screw.-EXHIBI

TIONER AT ROYAL COLLEGE OF SCIENCE.

[4482.]-OVAL.-" Symmetrical Beauty," by D. R Hay, is the best book on the subject I ever met with, 8vo., 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. B. M.

[4490.]-WELDING CAST STEEL.-If "T. O. B." will take great pains in heating his steel, by watching it in a nice gentle fire kept free from dirt, and use the following composition, he will have no difficulty whatever in doing it to his satisfaction:-Take ten parts of borax and 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 the sledge-hammer. A small 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.-BENAR DIN.

[4499.]-"FOUL AIR."-The cause of foul air in mines and other places is the presence of decomposing animal or vegetable matter. The gases more frequently present in mines are marsh gas (light carburetted hydrogen) and carbonic acid gas. The former is given off to a great extent from seams 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 CH4. By means of the safety-lamp of Sir Humphry Davy, accidents might in almost all cases be 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 the 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 be got rid of by proper means of ventilation. In large mines 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 used for forcing pure air into the workings of mines.-EXHIBITIONER AT ROYAL COLLEGE OF SCIENCE.

[4503.]-MENSURATION OF SUPERFICIES.-The rule "T. W. H." has been trying 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 be more used than it is; being much easier than the statements of the rule commonly make it appear, and the three sides being 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 say, a "three-sided triangle" was quite conceivable without the diagram, especially as no use or mention is made by him of D'or the line DB:

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showing the next figure to be 5, and so on. He most likely boggled at the second line of the evolution-the line always the most needing attention. Books do not say, as they ought, that the second figure of a square root must never be written, unless it be a 0, 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, as 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, 52, 53, he will find a terminating root; their areas being commensurable with the square of a side.-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 A B carries two studs which slide in the grooves of the crosspiece. By turning the traverse bar a pencil point at C is made

A

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.

[4504.]-ELLIPSES.-I suppose the cheapest and best to be "Cowper's Ellipsograph," made by Holtzapffel, because you can strike the curve (half at a time) with pen at once, and its range 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 drawing, 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 mine only requires setting for the major axis by a scale attached, and the minor axis must be right. Mine would cost a great deal more than Cowper's to make. See 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 by him, "Cowper's Ellipsowhich is more extraordinary still. graph" 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 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 ball being 28 times the wire's diameter, its section is exactly 784 of the wire's section; so that a

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cylinder 7in. by Tin. would equal 734 times in and the globe being of the cylinder, is of the wire.-E. L. G.

[4511.]-WEIGHT OF BALL-Its cartes, product of radius and surface; and the v its great circles. A circle of Tin. dist 22 round, has nearly 11 x 31 square is le surface of ball is nearly 154, and its cases, 3 = 1794 cubic inches, about 450 in wrought. In the other questi commensurable, that of 7in. dia 28 x 28 of a quarter inch, a cylinder 7in. long would give 784 times 7in. ball, being always of its containin the above quantity, or 3,658 in. of a ball's content only is wanted, 11-2 cube is near enough.-E. L. G.

[4512.)-REVOLUTIONS OF BL. number of revolutions conveyed t another is inversely as the diamete Thus, suppose the driving wheel er meter of 6ft., and makes 40 revolutis and the diameter of the driven wheel i 3:6::40:2. Thus = 80, the number of the smaller wheel. Of course, the tions will be much greater than this in three posed by "Ralph," but the principle is EXHIBITIONER AT ROYAL COLLEGE OF SE

[4512.] REVOLUTION OF BLAST method I invariably take to reckon up n blast fans might answer Mr. "Ralph." I s the first place, diameter of pulleys, likewie revolutions of first mover per minute. Th by simple proportion-viz, diameter of pal mover divided by diameter of correspondo The quotient, multiplied by number of reve Arst mover in a given time, gives speed of secen: or counter shaft. Again, diameter of tra pulley, divided by diameter of pulley on fan a the quotient, multiplied by number of revelata second mover or counter shaft, gives the speed is driven at. I have a model of blast fan, the pris of which is quite original, so far as I know. The> sides or cheeks are concaved two-thirds entire with fan, with an aperture to admit air; said aperture cres by a bridge on each side, for carrying fan spinde To curved blades, formed to suit convex side of cheeks, an secured to a disc. The casing or periphery servient ing disc is placed excentric to same, with breakers crossing space at variable angles to relieve pressure of fan; the whole, connected by tie-bes, with me! method for driving and discharge, needs consret. Will any of my brother mechanics expas an openin on its merit?-WILLIAMS.

[4512.1-REVOLUTIONS OF BLAST FAN.-Le "Ralph" divide the diameter of drivies alley by dia meter of smaller one, then multiply resalt thus obtained, by number of revolutions of larger palley.-W. E. THORPE, Reading.

[4518.]-HORSE POWER.-In this query the pressur of the atmosphere is excluded, as its action and reaction on the indicator is equal and contrary. Hence the f8 v 83000 formula R = engines; and, R =

(1) is correct for non-code!
j (s + p) c
83000

[graphic]

(2) is correct for c

densing engines. But should the atmosphene preaure be included in the application, the foamsh R = f (8 - p)'v (1) is correct for non-condensing engines

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33000 and R (2") is correct for condensing engines Lastly, since both pistons go at the same speed, the 262 + 152 4

ratio of expansion p

logarithm of 1

is = 3.7

152

=

The Napier

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2-3 14+1 = 94 x84 861b. mean pressure throughout the stroke v introduced in formula (1), will give the theoretic AR. D.

[4517.]-STAINING GUT LINES.-I think the be colour to stain gut lines is a kind of greyish grees, it is rather a troublesome process to undertake. Be cupful of black tea in a quart of water, allowing th to remain in till it has acquired what is called the water stain," when it should be rinsed in cold w allowed to dry. Then put a handful of logwood day into a quart of water, and boil till the latter is redo a pint. Take it off the fire and throw into it a pia blue vitriol previously powdered; stir until the is dissolved, when the gut may be put in and ke till it acquires the desired tiut. It will not take minutes, and the gut should be rinsed in cle directly it is taken out of the dye. For a slate stain, which many prefer, a mixture of boiling w ink is amply sufficient, always remembering to can likewise be coloured by any of the aniline dyes gut thoroughly when the right tint is obtained at the chemists, but I think they might possibly its texture.-A. T., Staines.

[4518.]-MYROBALANS.-This is a fruit which g in India, and is largely imported to Europe on acco of the tannin which it contains. The myrobalan is pale buff colour, and resembles a slightly shrivell plum. It consists of fibrous cellular matter envelop a stone. It is hard and firm, and when beaten with hammer breaks up into irregular fragments and light-coloured dry powder. As myrobalans are cheape than galls and stronger than sumac, they are rapidly superseding those articles. With preparations of ir they dye cotton stuffs a fuller black than can be obtaine by sumac.-DYER.

[4518.]-MYROBALAN.-A kind of dried plum broug from the East Indies, where it is used by the Hindoos medicine and calico printing. It has an unpleasan bitter taste; produces with iron a durable black dye ink, and with alum a dark brownish yellow.-T. W.

BOORD.

[4518.]-MYROBOLANS.-Myrobolans is a bitter fruit brought from India, and used by calico-printers, dyers, &c., for dyeing black and yellow.-BEACON LOUGH.

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519.]-PHOTOGRAPHY.-Procure some good ben,place it in a plate and apply moderate heat until quite fluid, pour it into a cold plate and when quite it may be broken in pieces. Then dissolve loz. of fused benzoin in 8oz. of methylated alcohol and 20 of sandarac. Then add 20 drops of mastic ish, made by melting gum mastic and adding tur: tine to it whilst in a fluid state. The impurities will settle, and it is ready for use. Should the varnish Do thick add more spirit.-H. J. KINGHAM. 520.)-PERCH FISHING.-I think the best time to for perch is from September to January in large deep ies and ponds by the side of a river. There are ibers of these in the Thames, and excellent perch ing is to be found near the paper mills at Temple, r Marlow. Weirs are the best places in summer e, but perch are not in first-rate condition then. ere are several methods of fishing for them, and of irse different kinds of tackle. I think the most sucsful in the Thames is the method known as "paterstering." Attach a lead to the end of a gut line about or 5ft. long, and about 3in. and 15in. above it two ort pieces of gut, about 4in. or 5in. long, with No. 8 9 hooks fastened so as to stand out at right angles. it with a live minnow or gudgeon-the hook put rough the upper lip. A longish rod, with a free-running e, I have always found the best. I prefer the plaited kink" k lines myself, as those made of silk and hair quently and are very apt to hitch instead of running e; besides, they are not so strong as the plaited silk. hen all is prepared, with the lead hanging 6ft. or 7ft. om the top of the rod, drop the line gently into the ater till the lead rests on the bottom.

Shift the bait

[4546.]-LATHE, &c.-TO "BIERLALA."-If you are limited to three rows of divisions, I think 180, 96, 84, are perhaps the best. I am strongly in favour of a row containing 11, 13, 17; also 19 and 14, if your diameter is sufficiently great, else the 6th and 7th of the 17 row come too close to the 9th and 10th of the 19 row, unless your holes are extremely small. Less than 7iu. diameter will scarcely hold them. I have this very day done the fitting of my new 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 to try it-single-handed I mean, of course. My hardened fast-collars are coned with the slide rest set 1 taper for the inside of collar, and deg. or 30min. taper for the outside of collar and the inside of 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 last line appears to be a misprint. The loose collars fit tight on to the 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 tempered at all.-J. K. P.

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

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720 360 200 144 120 112 ery now and then; don't strike directly you feel a 11 witch, but "bide a wee," and when you feel a second tack tighten the line, and give a sort of "lift," as the (I may add that Edwin Baker, of 14, Mount-row, erch is rather a delicate-inouthed fish, and if you Berkeley-square, London, issues a list gratis of the strike" hard you are apt to lose both fish and bait."Ready Reckoner for the Dividing Plate;") but there are erch generally swim in shoals, so if you succeed in also found useful for some amateurs who do very fine anding one keep to the same place. There is another work these numbers, say— ethod of fishing for perch, which consists in baiting with brandlings, and using either ordinary tackle or the Nottingham style. A few broken worms thrown in now In these methods nd then will often attract the fish. et the float be carried well under before striking.-A. T., Staines.

[4521.)-EXTRACTING HONEY FROM THE COMB. -Cut the comb in pieces with a sharp knife so as to divide all the cells, and place the pieces in a colander over a basin or jar to receive the honey as it drains off.

T. W. BOORD.

[4522.]-PURE CHARCOAL.-I am rather puzzled by Mr. Ibbotson's query. Does he inean what we, as chemists, call pure charcoal, or what druggists sell as such-a very serious difference? Pure carbon is almost impossible to obtain, except in the form of the diamond, Lut a "pure vegetable charcoal" is made by carbonizing willow or other wood in an iron retort. I imagine "What kind of fire and hot plate is pure ?" must refer to this. For such a purpose, with an iron retort fitted with an 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.-SIGMA. [4524.]-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 can bring the boiler nearer to the engine, or vice versa, by a telescopic joint made secure by a stuffing-box.-D. CLARKE.

[4528.]-CARVING AND TURNING SOFT WOOD.For external surfaces use the gouge and chisel. The insides of boxes, &c., are shaped and finished with what are called hook-tools; their form varies with the taste and requirements of the operator, and considerable practice is necessary to use them properly. The screws are cut with a rough kind of traversing mandril. The 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 palleys. "S." will easily comprehend its working from this brief description. If not, let him devise the working of a ship's rudder by the "wheel"

the principles 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 focussing is concerned, the fine movement may be dispensed with where the chain movement is used, but the fine movement, if well made, is useful for micrometrical 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 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 parallel inside, most decidedly, all the way to the top. WAHSHOF.

[4540.]-MOUNTING PLANE MIRROR IN RE FLECTING TELESCOPE.-Mr. A. White's plan would fail. Herschel shifted the optical axis of his telescope parallel to the tube, and so brought it close to the side. Mr. White shifts his angularly within the tube, which will have no other optical effect than he could get by sting the tube with the mirror. If he will consider his picture he will see that, without some as yet 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 as lie in the direction of the axis of the mirror; and very little of them, since he gets the tube (the lower half in his figure) in the way, and only the extreme upper edge of his mirror (as shown in the figure) would be available to form an image.-R. A. PROCTOR.

[4543.]-TORTOISE-SHELL COMBS.-The edges of the fracture should be scraped smooth, so as to overlap each other, and freed from grease, then dipped into hot water to sotten them, pressed together with hot tongs, and lastly, plunged into cold water till hard again.-T. W. BOORD.

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and Holtzapffel's lathes, to some of them were put these individual numbers, 221, 209, for very fine rings or flutes, when you use them 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 are formed and modified by surrounding conditions.-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, 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 so as not to be allowed to come to ear till the next season, the product will be found to consist partly of rye or some other of the 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 persons, that it can no longer be rejected. And it appears that poorness of soil has the same effect as mowing down. One observer 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 Gardeners' Chronicle, 1846, pp. 118, 102, and August and September, 1844; also Mag. Nat. Hist. new series, i. 574; and Rep. Roy. Soc., 1846, p. 381.-W. P.

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[4548.]-IMMERSION LENSES.-These lenses possess the great advantages of being easy to work, ard of possessing greater penetration" than a "dry" lens. Their price will vary from £3 for a German 1-16in. to £50 for an English 1-50in. 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's advice to persons about to be married-" Don't!" He will find an English fin. 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 lin. may be pur chased for about £4, but I question the utility of apply ing the immersion principle to lenses of these long foci.-H. P.

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[4552.]—AVIARY.-The best time 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 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 If "Rebaf" purchases any, let him get the aviaries. live more than two years in this country. Norwich birds, or the Yorkshire-German ones seldom 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. 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 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 so far as the law of pendulum motion, he is in a sense correct, although stated in such a common-lice 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,-that is to say, that a pendulum may vibrate in an arc of 7 or an are of 4, and its oscillations be isochronous or nearly so. The raising of the bob shortens the centre of oscil. lation of the pendulum, and thereby shortens the time of its swing, but makes no alteration in the time it takes to oscillate in a large or small are of a cycloid, or in a small are of a circle. Your correspondent should read "Clock and Watchmaking," by E. B. Denison, M.A.-ELECTRO-MAGNET.

[4554.]-THE PENDULUM.-" Vibrator" is in error respecting the pendulum. The following are among the laws of the instrument:-1. At the same station, pendulums of the same length move through cycloidal ares, whether long or short, in the same time. Common pendulums, which oscillate in circular ares, practically possess this property when their arcs do not exceed 2. The tines of oscillation of pendulums of 5 or 6. different lengths, vary as the square roots of 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 any cause, the clock gains or loses lowered from accordingly; and hence the necessity for compensation pendulums.-W. P. [4563.]-BRASS COIN.-This is a jetton or counter of the time of Queen Anne. They were used for calculating. The word jetton is derived from the French verb jetter, to throw or cast; hence to cast up an account.-T. W. BoORD. INSTRUMENTS. MATHEMATICAL [4567.] 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 splendid set some time since for 30s., but there seems a prejud ice against them. The pens are never so good as Ellio tt's, but whose are ?-J. K. P.

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[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 locus, 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 common" policeman, but go to head-quarters and any 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 the courtesy (as I would) to show their authority for the restriction; and if there is an 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 83rd Vic., cap. 99, The Habitual Criminals Bill,' sec. 17, it is enacted:" Any dealer in old metals, as defined in the Old Metal Dealers; 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 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, 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.

QUERIES.

[4572.]-GEOLOGICAL.-Near Malvern are some limestore quarries. Can any of your numerous correspondents inform me to what formation they belong?— PHILOSOPHER.

[4573.]-METHYLATED SPIRIT.-Can" An Associate of the Royal School of Mines," "Beta," or any other reader of the ENGLISH MECHANIC, inform me if there is, at times, 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.]-PARAFFINE OIL.-Can any brother reader of 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 ?-A POOR

MECHANIC.

[4575.]-ENAMELLING WATCH-CASES.-Will some other reader kindly inform me how enamelling is done on the backs of gold watch cases, &c. ?-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 microIf they would scopes and telescopes is blackened with? 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 in paraffine, answer as well as gutta-percha tissue to insulate the layers? and how much would be required? "Sigma" would give a working description of what he considers the best plan of coil to give a spark 3in. or 4in. with 4 Bunsen's cells, he would oblige.-OPERATOR.

But if

[4578.]-STRETCHING GUT-BAND.-Is there any way of permanently stretching a new gut-band 2in., which is about 8 yards long, and in. in diameter?T. E.

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