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very-day electricity indeed, and hence their value lightning preventors, not attractors. You can dis re, silently and without shock, the largest electrical try, by simply holding one pole while you present arp needle toward the other. In this way there is oubt every right lightning conductor helps in a to discharge the clond silently, and prevents hes that would, without it, have occurred. But in excessive tension of storm electricity this purpose 10 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 ntiful "attractors" and a broken bar end in sunae, but not in a storm. If anything can be said to cact lightning it is the pointedness of the whole Jding or rising ground. Spikes make no difference, knobs as big as any dome; and nothing can be more surd than carrying ont conductors an inch above or one 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 elecical 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 e ground up "to the metal gutters," it is 80 far solutely 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 1 gutters, or inside, by descending a chimney. No onductors to the ground then are ever wanted,-you 1ave them already-but simply from chimney tops, or other "attractors," to the nearest gutters. Whatever metal 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 Inade 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.

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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 d this generation. Nowhere but among percentagers could it now occur, any more than destruction of hisetoric monuments, or fifty other crying Bedlamisms of the time.

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E. L. GARbett.

So

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[279] SIR,-I wish to ask the author of the [282] SIR,-In answer to "E. T.'s" question, asked Almanac" is it stated that the sun is in the constellation to a curious discovery recently made by M. Bazin. "Astronomical Notes" on what page of the "Nautical some weeks since, allow me to call his attention Gemini on the 1st July, 1870. On the contrary, we The time required for the exposure of a plate find in that work, as well as in several others on is now very short, but if the author's observations be astronomy, that the sun is stated to be in a certain good for anything this time may be diminished at least sign of the zodiac, and to have so much right ascension one-third by adopting the plan to be described. It will and declination. It is, indeed, "nonsense" to infer excite astonishment to learn that the plan consists in that he is in a certain part of a constellation from these admitting to the camera light which does not pass ares; because the point of intersection of the equator through the lens. M. Bazin makes four holes in the front and ecliptic is ever varying. The fixed meridian of of the camera, and fits them with glass coloured by a Greenwich, as it will be readily perceived by every one solution of carmine in ammonia, behind which he who has given this subject any consideration, is not, places another piece of unpolished glass. These holes therefore, a similar case. In thousands of years hence are uncovered at the same time as the lens, so that the would not "F.R.A.S." say that the sun was in the same red light falls upon the plate simultaneously with the constellation, because his R. ascension was found to be image through the lens. According to the statement of quite different? How otherwise, then, I ask can the the author the blacks and high lights are by this means "inference or conclusion" in question be anything much softened and the half tones greatly improved. G. FIRTH. but "illogical." 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, mention that M. Bazin has tried other colours, but finds and we must content ourselves by calling the notice of our photographic readers to the discovery. I may red to be the only one which gives satisfactory results.

LUNAR MOTION.

[280] SIR.-I have received the ENGLISH MECHANIC and must state that I am much pleased with the change. since Scientific Opinion has been merged into it, 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.,

Toronto.

ANDREW ELVINS.

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 π, 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

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.

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

TION.

hat of descending; and the third and fourth strains are

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[278] SIR,-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 whole of the bass is the diatonic. In the first strain it wants the sub-dominaut; in the second strain it certainly is the diatonic scale 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 leading note of the third strain in all the four harmonized parts should be omitted.

ARTILLERY DISCHARGES AND RAIN. [281] SIR,-Your correspondent understood 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 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 clondy weather which I have spoken of, this subject would not have been

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22

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 estiL. H. C.

mation.

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 illegibility is necessary or favoured in commercial circles, flatly deny, whatever may be the presumed rapidity of thought thereon attendant.

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[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) ex-
presses 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 dis-
cussion; 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 care-
fully 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 re-
modelled 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 de-
scription 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 know-
ledge 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 pheno-
mena 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, pro-
jecting 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. PRESTON.

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 contain half a bushel. A box 8in. by 8in. square, and 8in. deep. will contain a peck. A box Sin. by 8in. square, 44in. deep, will contain one gallon. A box 7in. by Sin. square, and 4 in. deep, will contain half a gallon. A box 4in. by 4in. square, and 44in. deep, will contain a pint.

EXTRACTS FROM CORRESPONDE

A WORKMAN'S TESTIMONY.

Brunswick-road, Sheffield, says:-Th
for some time to express my approbatia
add any testimony to its value. Ba
spondents. I have subscribed to m
tone of some of your recent
periodicals for about twenty year
such satisfaction from one befor
many points of interest contains
the rest being the articles on Che
'Science for the Young, Music, n
the Correspondence Columns. li
Ic ould point out three or four of p
whose hands I should like to gr
personally for their contributions,
perhaps be something novel to the
hands grasped by the somewhat bed
of the sons of toil. If some of
men, who spend their time and mone
would contrast one number of outs C
pot of beer,' I think they would at
that they pay "too much for their whisth

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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 bac The diagrams explain the rest.-REED TUNER.

[8949.]-REPUBLIC OF GUAIANA.-I am quite s 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 tha that I believed it was near Venezuela. I answered to the query about the "Republic" of Guiana I think even

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

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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 voëрy, “ 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, rtion of South America that the Oronoco, by its que bifurcation, detaches and isolates. Rising about Zaiddle of this vast tract, its first course is S. W. and Award, directly from the sea it is to reach; then, in heart of the continent, it splits into two, to the S.W. N. W., each equal in volume to the Rhine. The aer 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 an; and thus we have the only river in the known rld that, like Adam's in Genesis, is "parted," and a compasses 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." contines 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 Srdly 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 ot been moved, but very variously named, being the San Come and Nueva Guayana of old maps, afterwards ngostura, now lastly Ciudad Bolivar. This quarter, qual in extent to France, all drains to the Oronoco. he only low, moist, and unhealthy Guayana is the reaining or maritime part, comprising the three poor -olonies “J. G." has alone mentioned, where the ritish, Dutch, and French have scratched but the nerest margins of low coast. It is remarkable the gold liggings discovered only three years ago in a high and cool table-land of Venezuelan Guayana, had been heard

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1 by Raleigh, and for two centuries regarded as a fable.

-E. L. G.

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 impenetruble wood 20ft. Ligh-and it must now or shortly differ little in social and physical state from a bit of central Africa, savo 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 probably 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.

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 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. 137, 391, 417, 462, 518, 640, and 660.-CURRENT.

[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. LEG. IV. I find it quoted in one of MM. Lincoln's catalogues, 2s. and 3s., according to preservation. Plated varieties are existing.-BERNARDIN.

[4418.)-SILVER COIN.-A Roman Family Denarius;

[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.

[4448.] TRUE MERIDIAN.-A "Young Surveyor" will find that the best way to obtain the astronomical meridian in the field is by compass, allowing for the variation of the 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 query 4342 (August 5, p. 477) contains the results of determinations in 1868-9. Practical treatises on navigation give the method of finding the magnetic variation, from which, as just stated, the true For the determination of a fired meridian line refer to p. 285, is easily found. June 10, reply to query 2558, Sundial.-W. R. BIRT.

meridian

to

[4226.]-DOUBLE STOCKS.-I quite agree with "Norma" (although only an amateur too) that the best plan to save seed to raise double stocks from is to destroy all flower pips on single flowering plants that have only four petals, and to save the seed from those with [4461.]-SCREW CUTTING.-I am not sure that five, six, or seven petals: the more petals, the better the onto is a dictionary word. Perhaps your compositor seed, although I never saw a pip with more than seven has done rightly in altering it to into in my letter, on petals bear seed, and then only on the Giant or Bromp-page 525, but he has spoilt my meaning, while improving ton Stock. I never saw more than four petals on a pip my grammar. I remember the same thing once before. of the single-flowered annual Dwarf or Ten Weeks'-J. K. P. Stock.-W. E. CORDON.

[4340.]—FROM N. G. LAMBORNE.-N. G. Lamborne's velocipede was a four-wheeler, with the ordinary crank motion, driven by the hind wheels, 8ft. diameter; front wheels, 2ft. diameter; crank, 64in.; swinging treadles, 6in. joint at crank, and 4in. joint which holds the treadle to the frame near the front wheels; frame 5ft. long, extreme 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 management in placing the seat and treadles. I do not advise

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

[4467 and 4551.]-IMPRESSIONS FROM PRINTS AND TRANSFERRING ENGRAVINGS TO WOOD.

[4131.]-SUNDIAL.-W. H. C." will find a letter on page 46, Vol. X. of the ENGLISH MECHANIC, which may help 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.)-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 any one to make after this plan, although it is the best pressed together for a minute or two in a copying press. 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. 375, 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 spirit level 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.

no

[4174]-GEOLOGY.-"Veritas's" question cannot be replied to positively. It must be a time almost beyond computation-millions of years certainly.-AUGUSTUS. [4190.]-EMIGRATION TO THE WEST INDIES.— Two things are to be borne in mind-1, that in the globe's warmer half, viz., in latitudes below 30, wood clearing (which is the first essential) nor any out door manual labour can be performed by Europeans, except at elevations above 8,000ft., or at least 6,000ft.; 2, that nature has not, in the tropics, made the exploita tion of a labouring class, however poor-and least of all when they are freed slaves or their descendants-by a richer directing class, possible as she has here. Now, of the British West Indies (though nearly all are hillier than the summit of Scotland), none contain ground high enough for whites to work on, except the part of Jamaica east of Kingston. On these mountains, I believe that Englishmen, or at least "temperance 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

men,

that I have seen, except an invention that is now nursing.

-N. G. LAMBORNE.

[4368.)-LINING-OUT SHAFTING.-Cut a semicircle (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 indicate the contre line. pedestal to the next, and so on with a good spirit level, Level from one wood in 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 Apocynee. 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 mulberry 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 nearly the whole of the revolution. Now to satisfy myself, thisweek I took off the head of the heater 12ft. from where the water entered the exhaust pipe and watched the work of it with 101b. of steam, and instead of back pressure I had a partial vacuum when the greatest rush of water occurred, so much that the steam returned at that particular point with considerable noise; that point leave the pipe for the open air. Again I can get no loud can be seen with steam at 40lb. in the puffs as they and clear bark from the exhaust when pumping as I can when the water is shut off, and I certainly think the engine works easier when pumping than not: but one point I do not understand, my exhaust pipe direct from the cylinder is 12ft. long, and when I first tried it in 1863 I blew into a close cask of 120 gallons. Then I had twice as much silex deposited on its sides as I do now I have replaced it with an iron one as being more orthodox; I presume the reason is because the wood is the best non-conductor of heat.-ONE EYE.

[4416.]-PHOTOGRAPHICAL.-If "John" is thefortunate possessor of the fourth Volume of the ENGLISH MECHANIC, he will find all he requires, I think, in the exceedingly good chapters on "Elementary Photography," by "A. H. W.," on pp. 25, 41, 89, 116, 201, 250, and 285 in that Volume.-CURRENT.

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 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.

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

[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

the handle is turned; it also has a small hole in it for It will be the wire to pass through on to the coil at A. 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.

calculating the power of a steam-engine is 7854 d4 p r =

[4474.]-HORSE POWER.-The common rule for

550-horse power, or d3 pv = 700-horsepower-(a). But as the steam should be stopped off at the stroke.. dep v 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 d2 have by division d2 = 10 H. P. .. H. P. = 10 nal power of non-condensing steam-engines. And substituting 71b. per square inch instead of p in equation (a) de 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,

= nomi

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.] BOOKS. The "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, Or 2, dilute sulphate of indigo and it is ready at once. 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.

[4503.]-MENSURATION OF SUPERFICIES.-The cylinder 7in. by Tin. would equal 734 times in rule "T. W. H." has been trying for a three-sided triangle, and the globe being of the cylinder, indy namely, that the area is the square root of the continued of the wire.-E. L. G. 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 D B:

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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

[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 what-
ever 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 to describe an ellipse by the rectilinear movement of
his swaige; put in a piston, and use the sledge-hammer. the studs in the grooves. I believe this instrument was
A small quantity of this composition will be sufficient, described in the Mechanic shortly before its absorption.
sprinkled on the parts to be welded while in the fire.-T. W. BOORD.
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 CH. 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 In may be got rid of by proper means of ventilation. 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.

[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 a
pen at once, and its range is very large, compared with
mine, which toe, 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 dia-
meter 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,
which is more extraordinary still. "Cowper's Ellipso-
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 com-
pare one round body with another, as a ball with wire,
any reference to or its parts, 7854 or 5236, is
of place, and indeed absurd, as the solution will be ex-
act 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

out

[4511.]-WEIGHT OF BALL-Its contes, de product of radius and surface; and the its great circles. A circle of Tin. disme 22 round, has nearly 11 x 31 square index surface of ball is nearly 154, and its c 3 = 179 cubic inches, about 4 50 in wrought. In the other question be commensurable, that of 7in. diaz 28 x 28 of a quarter inch, a cylinde 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, 11cube is near enough.-E. L. G.

[4512.)-REVOLUTIONS OF BL1-The number of revolutions conveyed proto another is inversely as the diamete Thus, suppose the driving wheel er meter of 6ft., and makes 40 revolutio and the diameter of the driven wheel ki 3:6::40: r. Thus = 80, the number! of the smaller wheel. Of course, the Y tions will be much greater than this in the posed by "Ralph," but the principle is er EXHIBITIONER AT ROYAL COLLEGE OF SE

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

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

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2) is correct for c

[4513.]-HORSE POWER.-In this query the press of the atmosphere is excluded, as its action and reaction on the indicator is equal and contrary. Hence the f8v (1) is correct for non-coded 89000 formula R = j (8 + p) c engines; and, R = 33000 densing engines. But should the atmosphere be included in the application, the msk R = (8 - p)'v (1) is correct for non-condensing engines f8 v 33000

33000 and R =

(2") is correct for condensing engines Lastly, since both pistons go at the same speed, the

ratio of expansion p

262 + 152 4
152

4

logarithm of

is = 3.7

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2-3 14+1 = 94 x44861b. mean pressure throughout the stroke v introduced in formula (1), will give the theoretic AR. D.

[4517.]-STAINING GUT LINES.-I think the best colour to stain gut lines is a kind of greyish gree it is rather a troublesome process to undertake. B cupful of black tea in a quart of water, allowing the 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 da into a quart of water, and boil till the latter is red a pint. Take it off the fire and throw into it apar blue vitriol previously powdered; stir until the is dissolved, when the gut may be put in and kepa till it acquires the desired tint. It will not take minutes, and the gut should be rinsed in cles 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 w 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.

G

[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 e pale buff colour, and resembles a slightly shrivelled 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 cheaper light-coloured dry powder. As myrobalans are than galls and stronger than sumac, they are rapid 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 Hindoosi medicine and calico printing. It has an unpleasan bitter taste; produces with iron a durable black dye a 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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[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, 18, 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 7in. 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.

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 arc of 4, and its oscillations be isochronous or nearly so. The raising of the 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 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 5 or 6 2. The times of oscillation of pendulums of 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 lowered from any cause, the clock gains or loses accordingly; and hence the necessity for compensation pendulums.-W. P.

519.]-PHOTOGRAPHY.-Procure some good ben-
1, 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
118 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
oo 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
abers 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 suminer
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 suc-
sful in the Thames is the method known as "pater-
stering." 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
k lines myself, as those made of silk and hair" kink"
quently and are very apt to hitch instead of running
ee; 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
very now and then; don't strike directly you feel a
witch, but "bide a wee," and when you feel a second
ttack 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-
nethod 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
and then will often attract the fish. In these methods
let 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, but a "pure vegetable charcoal" is made by carbonizan ing 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.

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[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.

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[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. WAHSROF.

[4540.)-MOUNTING PLANE MIRROR IN FLECTING TELESCOPE.-Mr. A. White's plan would REfail. 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.

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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 can-
not 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 selec-
tion," and its cognate doctrines, showing 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, 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 pro-
duct 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.

[4548.]-IMMERSION LENSES.-These lenses pos-
sess 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 con-
clusions as to the suitability of this kind of lens to
his requirements. Any of our leading makers would
show him their working. An English in. may be pur-
ing the immersion principle to lenses of these long
chased for about £4, but I question the utility of apply.
foci.-H. P.

[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 more likely to live when taken in the autumn. Canaries, being bred under domestication, may be obtained at any time, and are undoubtedly the best birds for aviaries. If "Rebaf" purchases any, let him get the Norwich birds, or the Yorkshire-German ones seldom live 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. 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.

[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.

[4567.] MATHEMATICAL INSTRUMENTS. Broken instruments are hardly worth repair. The plates are steel and brazed in, and could hardly be got out. Excellent French and Swiss cases of instruments are to be had for a song at the second-hand shops. A friend of mine bought a 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.

[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 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 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.

Vic., cap. 99, The Habitual Criminals Bill,' sec. 17, it [4570.]-A LEGAL POINT.-In the 32nd and 33rd Old Metal Dealers; Act, 1861, who shall either personis enacted:" Any dealer in old metals, as defined in the ally 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 for copper, whether new or old, in any quantity at one or by any servant or agent purchase, receive, or bargain 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.

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the ENGLISH MECHANIC inform me if there is any [4574.]-PARAFFINE OIL.-Can any brother reader of 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 microscopes and telescopes is blackened with? If they would give a short description of the process it would oblige.— J. HAINES.

[4577.)-INDUCTION COIL.-TO "SIGMA."--I want to make an induction coil, and feel rather bothered with so many plans of construction that have been recommended." Inductorium" stated lately that the greatest inductive effect was at the centre of the coil, and nil at the two poles. Is it so, or not? If so, a partition in the middle of the coil would cause a loss of the best part of the electro-magnet. Will paper, soaked in paraffine, an[4554.]-PENDULUM.-Your correspondent "Vibra-swer as well as gutta-percha tissue to insulate the tor" has discovered a "mare's nest." He wishes to layers? and how much would be required? know why a clock should gain time by raising the bob, "Sigma" would give a working description of what he [4543.]-TORTOISE-SHELL COMBS.-The edges of as by the law a longer swing should be accomplished in considers the best plan of coil to give a spark Sin. or the fracture should be scraped smooth, so as to over- the same time as a shorter one ?" the law being, as he 4in. with 4 Bunsen's cells, he would oblige.-OPERATOR. lap each other, and freed from grease, then dipped into says, that a weight suspended by a silken cord will move hot water to sotten them, pressed together with hot in unequal spaces in equal times. In so far as the law tongs, and lastly, plunged into cold water till hard of pendulum motion, he is in a sense correct, although again.-T. W. BOORD. stated in such a common-lice manner. Yet he fails to

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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