employed and situated, who have used intoxicating drinks as beverages, and our unprejudiced opinion has been and is, that the abstainers were stronger and healthier men.-ED. E M.]

E.

[2543.)-THE NICOL PRISM-"The Nicol's prisma. which our readers will have seen mentioned so often in the recent papers of Professor Tyndall, are expensive to obtain of any size. They are made of a crystal of calespar. cut across diagonally, the two sections being afterwards joined together by means of Canada balsam. It has recently been discovered that a prism, possessing the sams optical properties, may be made by eonstructing a vessel of glass, inserting a thin plate of calc-apar across the diagonal, the vessel being filled up with bisulphide of carbon. If this be so, Nicol's prisms of considerable size may be made cheaply, since blocks of cale-spar of conFebruary 26, 1869. I eat the above from a scientifle siderable size are often met with."-Mechanic's Magazine. periodical. Has any subscriber met with it, and, if so, I should be glad to obtain further details ?-CARTHUSIAN. [2544.]-HEATING WATER IN BATHS-L there not a patent apparatus to be placed in a bath to heat it in a short time?-A. M. M.

prising. Can any of your readers give me any information as to the durability of the india-rubber wheel tires? I have seen on hand-trucks at railway stations similar tires. How do they wear? I should be afraid the rough [2512.]-SODA CRYSTALS.-Thanks for G. stoned roads would destroy the tire of the steamer. Also Davis's able article in No. 261 of your publication, but although the tires doubtless will expand under the pres sure of the steamer, still the weight must be there, and not having any drying or heating apparatus, I must abandon the idea of commencing the manufacture, how can they be prevented sinking on soft land?-AGRIand having two pans, both idle, one to contain 120 CULTURE. gallons, and the other about 80, I should like to know [2531.]-BRAZING CAST IRON-The impression for how to manufacture an article of simple process, and April 8th contains an answer to my query from "Blue marketable, to keep them going these bad times. Being Ruin;" my best thanks to the correspondent for his no chemist myself, probably G. E. D. would kindly kindness. The method of laying the work in moulding suggest something.-SODA CRYSTALS. sand will not suit my purpose, and pouring melted iron [2513.]-TAR DISTILLING.-TO "FEU FOL-over the joint is not what I should term "brazing." I will LET.-Will "Fen Follet" be so kind as to describe define more particularly the information I seek. I very to me the process of tar distilling; how long it is frequently have to repair important bright parts of The boiled before the pitch is run off; how to separate the machinery, cast iron (small pieces generally). articles when the pitch is run off, such as naphtha, defects are caused by friction. I file a slot in the cast oil, benzole, carbolic acid, ammonia, crude anthra- iron, and fit a piece of wrought iron in its place to comcene, &c., or where can I procure a book that will tell pensate for wear. My difficulty is this: I cannot get the what I wish to know; the price, and where to be had? spelter to unite the cast and the wrought iron-it has an -T. BROWN. affinity for the wrought iron, but will not take on the cast iron. It can be accomplished I am certain, as I [2514.]-SPICE MANUFACTURING.-Would any brother reader tell me where I can get the informa-have seen specimens of cast-iron neatly mended by tion how to make spice, or where I can get a book to brazing pieces of wrought iron to compensate for wear. tell me; also the means to colour it, price of book, For the information of St. George, I can assert that the process of Mr. Armitage, of Kirkstall, for case-hardening, is not new. I have seen prussiate of potass used in the way described twenty years since. I always use prussiate of potass for hardening my work (wrought iron), if there is much friction, especially bolts and pins.-RECIPROCITY.

and where to be had ?-T. BROWN.

[2515.]-BOILER-A few days ago I was told that if a boiler, the first time it is used is made to get up steam quickly, it will ever afterwards be easy to get up steam. If, on the other hand, the boiler is heated slowly on first using it, a difficulty will always be experienced in generating steam. Is there any truth in this statement, and if so, what is the reason?-W. H. THORPE.

[2516.]-EXPLOSIVE COMPOUND.-Are there any two liquids, inexplosive in themselves, which will, when mixed together, explode directly, or become cap able of being exploded; if so, what are they? In what proportion should they be mixed?-E. KENNEDY.

[2517.]-ELECTRIC ENGINE.-Is there such a thing as an engine worked by electricity of one horse power? What is its total size and weight? What the cost, and where could it be bought ?-E. KENNEDY. [2518.]-GAUGE FOR A KITCHEN BOILER. -Would it not be a useful and comparatively inexpensive thing to affix to all common kitchen boilers a small water gauge? It might be secured from fracture by being loosely cased in the manner of spirit levels, and its action having been once explained to the kitchen servants, I feel sure that many a boiler would be saved from cracking and uselessness. Is there any objection to this idea beyond that of cost ?-A. C. G. [2519]-VULCANISING INDIA RUBBER.-Will one of your readers kindly inform me how to vulcanise india rubber? Can the apparatus used by dentists for hardening vulcanite (which I possess) be used for the purpose, and how ?-GUMMY.

[2545]-EMIGRATION TO NEW ZEALAND.-Will "Josh." "H. Coggins," or any reader, favour me with a few hints, as I am going to emigrate to New Zealand? I have saved £48, and I am a single young man, a Jack of many trades, but master of none.-W. STONE. [2546.]-BATTERN-MAKING.-Will anyone be kind enough to tell me if there is any work published on "Pattern-making? If so, the price, and where to be had.GALLOWAY.

[2532.]-LEAD FOR "RELWOT'S" ENGINE.-(To
Mr. Baskerville.)-Allow me to congratulate Relwot for
obtaining such an excellent and valuable answer from
answer is worth pounds ia THE ENGLISH MECHANIC, not
our good-natured correspondent, J. Baskerville. Such an
only to Relwot, but to others as well. I wish to ask J. B.
one question-Why would he give so much lead to the
valves of the engine in question? I should have thought
4 in. lead decidedly too much for any stationary engine,
except it was a very high piston speed, as in my opinion
the piston speed is the main point to be considered when
deciding the proper lead for an engine. But I should
much like to see the question of lead well argued out in
these columns by some one that can fight, for scarcely
two engineers seem agreed upon this point. Will J. B.
kindly give me a single rule to find the proper weight
and size of engine fly wheels?-STEAM SPIRIT.
[2583.]-COCOA-NUT.-Will one of your numerous
readers be so good as to account for the milk in the cocoa-

[2520]-WATERPROOFING PAPER.-Can any of my brother readers inform me of the best method of making paper waterproof?-A. SPEIGHT.

[2521] CURIOUS AFFECTION OF THE TEETH. -Can any reader tell me the cause of the following strange affection of my teeth? Some time back a rough deposit began to be deposited on my teeth, till it had accumulated to the thickness of a sixpence, gradually covering the tooth and eating away the gum all round until the tooth fell out without pain, and scarcely any loss of blood. Nine of my teeth have fallen out in this manner. A druggist whom I consulted told me it was canker, and a doctor said it was scurvy; neither of their remedies did me any good. When the limelike coating, with which the tooth is covered, is scraped away, the tooth beneath appears to be as perfect as ever. Will some one help me, and prevent the loss of the rest of my teeth?-SUBSCRIBER FROM THE FIRST.

nut?-MINNEHAHA.

[2547.]-PRINTING NAMES ON PLANS.-Will some brother reader be kind enough to inform me of a method of printing the names of fields, trees, &c., on plans of estates? I have lately used a printer's pallet and type, but with not much success.-LAND SURVEYOR

[2534.J-SOLUTION WANTED.-The straight lines
AD, BE bisecting the sides B C, AC of a triangle inter-
sect at G: show that A is double of G D.-MINNEHAHA.
[2535.]-OLD COIN.-About 50 years ago I found, in an
old quarry, a coin, token, or medal; it is of copper, and
about of an inch in thickness. Enclosed is a copy,
size. It is corroded a little, and abraded on one side.

[2523.)-RUST IN WATER.-BREWING.-Will any of your numerous readers inform me the way to construct a cheap filter, which will separate rust from water; also has water, impregnated with rust, any injurious effect on the brewing of ale, especially as to flavouring it in any way; also the best and cheapest form of attemperator for checking the rise of heat in a fermenting square, dimensions 6ft. square, and 5ft. deep, usual length of brewing 25 barrels, temperature of water direct from the well 538 ?-CROMWELL.

[2524]-LONGITUDE.-Will some reader tell me the difference of time between Belfast and Glasgow? -SCIRE VOLO.

[2548] GILDING BATTERY.-Will any reader lend me a little assistance? I have a gildingbattery, Daniell's two cells, and cannot get it to work, as I am in error somewhere. The copper cells are about of an inch larger in diameter than the porous pots, which are 24 inches across. half-way up, and banked round at the top on the copper I have put sulphate of copper round outside of pot nearly rim, that keeps the pot upright, and filled op with water inside the pot to immerse the poles. I put oil of vitriol and water, one part vitriol and two parts water; but I could get no action on the poles. The wires-one from each-were ordinary stout copper, and I led them into some strong cyanide of potassium dissolved in water, and kept it over a gas-burner, putting a piece of 22-carat gold but I could make nothing of it. If any reader will set on one wire, and the article I wished to gild on the other. me right I shall feel extremely obliged.-ONE IN A FOG.

Will Mr. H. W. Henfrey, or any of your readers, kindly
inform me what it is, and if it is of any value?-TAFFY.

[2525.]-CONTENTS OF PART OF SPHERE.Will some brother reader inform me how to find the content of part of a sphere greater or less than a the two plane surfaces at right angles?-ANTHONY. [2526.]-SUBMARINE LAMP.-I have made several fruitless efforts to make a lamp some 3in. diameter by 5 or 6 long, that will burn under water. Could you get me any information on the subject? I want it to burn when submerged some 4 to 6ft. in fresh or salt water. I have tried a candle in a lamp fed with air by india-rubber tubing, but it went out speedily. Information as to the construc tion of such a lamp would oblige.-W. A. HACKETT.

[2586.]-ELECTRO-PLATING.-About twelve months ago I plated some tea-spoons, and they have a most disagreeable taste and smell when used for eggs, custard puddings, or plain boiled rice; I should be glad if some correspondent would kindly tell me the cause of this, and how it can be remedied.-A. R.

[2537.]-WRITING TELEGRAPH.-Is Meyer's telegraph, consisting of two cylinders having an isochronical motion, a new invention ?-THOMAS.

steel requires any preparation. If he will do so, he will very greatly oblige.-B. S. BURDEN.

[2551.]-THE SPECTROSCOPE.-It has often occurred to me that some of our numerous brethren who practise with the spectroscope might, if they were asked. give us a paper or two concerning the practical working of the instrument. And if any one has made one of these instruments at a cheaper rate than paid for at an optician's (of course it is not the elaborate construction of the instrument but its efficient working when completed, perhaps he will give a description and probable cost of making the same. It any will do this I think he will receive the hearty thanks of many others besides myself. -A. J. JARMAN.

[2538.]-INCRUSTATION ON POROUS CELLS.-
Could any brother reader tell me the best way for taking
off the copper incrustations on my porous cells, or suggest
a good means for preventing them?-ELECTRIC CLOCK.
[2539.]-OKE.-I wish to know the exact value of a
Turkish "oke;" a paper said lately it was equal to a kilo-
gramme. Is this not an error ?-CALCULATOR.

[2540]-SMOKE ON WALLS.-I beg to submit the following question to the investigation of the scientific correspondents of our E. M. I observe that, in a kitchen or any other place of which the walls have been whitewashed, the smoke is deposited on the whole surface of the walls and ceiling, with exception of the edges or intersections. What may be the reason of this? Are there at those places currents which prevent the deposition, or is this phenomenon of the same order as the one that is observed with the iodine vapours in presence of a relief or of an engraving?-V. M. BEECHY.

2541.]-GALVANIC BATTERIES.I have been studying for some time past the problem how to make I tried many substances, and heard afterwards that an economical, constant, energetic, and lasting battery. several had been already tried and had failed; might it not prove very useful to many readers to have a list of all the substances proposed or tried, with the results? This would spare much time and prevent waste: many readers could bring their brick to the building besides learned "Sigma," who has promised, I believe, to give us a note "On Batteries."-V. M. BEECHY.

[2527.J-ROSCOE'S LUBRICATOR.-Will some one of our practical correspondents kindly inform me whether Roscoe's patent lubricator lubricates the slide-valves of a locomotive engine when the engine is running with steam on, or only when the steam is shut off?-G. W. R. [2528.]-MUSICAL BOX-Would some kind and competent reader give a full description of a musical-box? I would be particularly obliged if some one would tell me how the uniform motion is obtained.-OMAR. [2529.]-INVENTOR OF THE MANGANESE BATTERY.-Will Mr. W. H. Stone," who gave a description [2542.]--PHOTOS. OF AUSTRALIAN SCENERY. of the manganese battery, state the name of the inventor-Would any kind brother reader tell me where I can of the same?-X. Y. Z. procure photographs of an Eucalypt tree, and of an [2530]-THOMSON'S ROAD STEAMER.-The ac- Australian acacia, or of an Australian landscape with coint in your paper of Thomson's road steamer is sur-those trees?-BERNARDIN,

dents inform me what the copper coin is, a copy of which I enclose-FLINT.

[2558]-SUN DIAL.-I have made a sundial, horizontal, and want to have the meridian line correct. Will some of our brother correspondents be kind enough to tell me the exact declination of the needle for the present time, as I can have access to a compass? I have asked three persons who used the compass in mines, and they all said it pointed north: not one of them knew there was any de elination at all, and one would not believe it until he asked an optic an, who informed him that it was so.-A. H. Z. [2550.-ANTIQUE.-I have in my possession a cornelian ring with an antique head cut on the stone.

The inside of the cutting is beautifully polished, and I lave been told that the secret of polishing the engraving is lost; is this so? Perhaps some of your readers, "gem collectors," would kindly inform me, or give me any hint whereby I could judge if the cutting is an setique or a modern one?-VIVIS SPERANDUM.

[2560.]-MICROSCOPIC.-I should feel under obligation to your microscopical readers who would inform me what is the view of first-class observers as to the lenses in the compound eyes of insects-the dragon-fly for instance. Do they consider the hexaronal piece is all lens, or that a minuter circular lens is fixed in this hexagonal setting?-F. F.

[2561.]-BOOKS.-' should be glad in reading of the sizes of books to be able to know exactly what is meant, as I am neither in the trade nor otherwise able to learn. My requirements are the sizes in inches of the page of all from imperial 4to to 32mo?-F. F.

[2562.]-HARMONIUM.-I intend to make a harmonium pan according to " Eleve's" instructions to a "Country Amateur, No. 245, page 279, but there are one or two things I should like to know before I begin, that is, the size of the reed hibs in the veneer at top and bottom, and also if the veneer is the very thin kind that is sold in the shops? I should think that the reed veneer at least would require some thickness in order that the reeds may be screwed to it. Perhaps "Eleve" would be so kind as to enlighten me on the subject. I would also take it very kindly if some of your harmonium correspondents would show me the way how two or more rows of reeds are placed in a harmonium-how the channels are connected with one another? I may mention that I have an apparatus under the keys of my harmonium by means of which a tune in any key may be played on the white keys alone, except where an accident occurs. when the black is used. This is done by merely shifting a small knob in front of the key-board, according to the key to be played upon. Perhaps some of your musical correspondents would say whether it is an improvement or not. It must be an advantage to those who would like to play a common tune in as easy a manner as possible, who are not very well versed in the mysteries of sharps or flats, as by this a tune in four or five sharps or flats is as easy to play as one in the key of C.-VALVE.

[256]-SMALL COPPER COIN.-Obv., a shield of arms, "A Halfe Penny, 1668;" rev., two men holding a piece of cloth, For the Poor of Dover." Why was it struck, and by whom?-OLD COIN.

2564.1-LEADEN COIN SIZE OF A HALFPENNY.-On one side a rude "W," on the other a device probably intended for an anchor. Should like information about it ?-OLD COIN.

255-HERBAL OF THE BIBLE.-Will any reader of the MECHANIC tell me of a book treating of the plants named in the Bible?-IXION. [2566]-TOOTH POWDER.-Will some brother subscriber kindly give a good recipe for a tooth powder?-INQUIRER.

(2507.)-CHIMING CLOCK.-I have a chiming clock, the weights of which are so heavy (281b. each) that whenever a line breaks, the weight, falling from a height of perhaps 5ft, has an unpleasant way of breaking through the floor. Can any reader suggest any means by which this may be prevented? I have thought of a bag filled with hay, or something similar, to be placed at the bottom of the clock-case, and so act as a buffer. In that case, what wonld be the best material to stuff the bag with ?-TooDLES.

[2568]-HARD WATER.-I find the Thames water is soft, but that the same water when it has passed through the water works gets hard. How has this change been brought about? Can anyone explain the mystery ?-STEADY HAND.

[2560.]-BAT HANDLES.-Can any of my brother subscribers tell me how to prepare and glue up bat

handles?-95, VOL. 4.

[2579.]-MALLET.- The enclosed drawing is a
mallet with a metal shell and wooden faces. It is
We have broken the one we
very useful in our trade.
had, and we cannot meet with another. We have

THE SIZE OF ATOMS.-Sir William Thomson, who contributes an important paper on the "Size of Atoms" to last week's Nature, thus sums up: The four lines of argument which I have indicated lead all to substantially the same estimate of the dimensions of molecular structure. Jointly they establish, with what we cannot but regard as a very high degree of probability, the conclusion that in any ordinary liquid, trausparent solid, or seemingly opaque-solid, the mean distance between the centres of contiguous molecules is less than the hundred-millionth, and greater than the two thousand-millionth, of a centimetre. To form some conception of the degree of coarse grainedness indicated by this conclusion, imagine a raindrop, or a globe of glass as big as a pea, to be magnified up to the size of the earth, each constituent molecule to be magnifiied in the same proportion. The magnified structure would be coarser grained than a heap of small shot, but probability less coarse grained than a heap

of cricket-balls."

THE COLOURING MATTER OF BLOOD.-Herr
for a con-
Hoppe-Seyler of Tubingen, who has
siderable time been investigating the colouring
matter of the blood, and has discovered that the so-
called Hæmatin is an essential product of its decom-
position, shows that this substance is a product of
oxidation formed immediately on contact with the air;
and, that, moreover, by decomposition of the colouring
matter of the blood, another substance, besides albu-
men, results, which he calls Hæmochromogen. Both
have peculiar effects upon light, which can be recog
nised by the absorption-bands in the spectrum, and
enables them to be distinguished. Both contain

iron.

THE LATEST EXCAVATIONS IN POMPEII, &c.-The Giornale di Napoli, of March 26, states that on the occasion of a royal visit to Pompeii on the preeeding day, some excavations were made in some houses situated on the right of the Via Stabiana, and a variety of treasures were found, viz.: a large number of objects in terra cotta, iron, and bronze, a beautifully-chiselled silver cup, a very rare glass oil lamp, a still rarer and perhaps unique object, cousisting of a small terra cotta cup with a metallic cup inside containing a night-lamp like those in modern use, a large gladiator's sword, with the metallic portions of the scabbard; many copper and silver coins of the time of Vespasian, and an amphora full of small onions near the skeleton of a woman. The skeleton of a man was also discovered, holding a pickaxe in one hand, au iron bar in the other, and with many bronze objects scattered at his feet, near a wall which had been partially broken through.

[2570.]-GLAZIERS' DIAMOND.-Will any sub-
scriber inform me how to soften the metal for taking
THE LONDON CO-OPERATIVE WATCH
out glaziers' diamonds; also, what metal is used, and
how to re-fix the diamond?-IGNORANCE.
MANUFACTURING COMPANY.-On Monday night
(11th inst.) a crowded meeting of the workmen engaged
[2571]-MATHEMATICAL TABLES.-Will any
kind friend inform me in which of the modern cyclo- in the various branches of the clock and watchmaking
trade in Clerkenwell was held at the Amwell-street
pædias is the best and fullest account given of the School-room, Pentonville, for the purpose of consider-
mathematical tables published to the present time.-ing the advisability of the trade, as a body, support-

W. H., Cinderford.

[2572]-LARGE FILTER-Would some person of experience advise me about a filter? I require about 5000 gallons of clean water every 24 hours. My water carries a considerable quantity of sand, insects, vegetable matter, &c., and is often during the day quite turbid. Could I construct a filter, using a large treacle or other cask in the manner described on page 578, Vol. X? Would "W. H. H.", 611, Vol. X., tell me where he got his "moulded carbon filter blocks"? Would common wood charcoal answer?-HYDRO. [2573.]-EOLIAN HARP.- Would someone tell me the best way to make an Eolian harp; also the best Katerials for same? A small drawing with measurements for one to fit in a common window sill would help me very much.-R. B

(2574)-BRONZING MODEL VESSEL. I am making a small model vessel, which I wish to bronze in imitation of copper on the bottom, and I want to know if the best copal varnish put on will cause the bronze to stick; if not, what wili?-ONE IN THE

support the London and Clerkenwell Operative Watchmakers' Manufacturing Company." Several objections to the schetne having been replied to, to the apparent satisfaction of the meeting, the proceedidgs concluded with a vote of thanks to the chairman.

A STEAM-ENGINE WITHOUT A CRANK.— The Milwaukee Daily News thus describes the performance of an engine, which, however, we fear our readers will read with considerable doubt. The engine is very simple, and consists of a cylinder 12in. lohg and 6in. bore (in one already built), with the shaft passing through the centre of it. The cylinder is furnished with a piston at each end, precisely like the pistons of common crank engines; to these pistons are connected short rods, with a friction roller at the outside end working in the inside of an elliptical ring, which passes around the shaft outside of the cylinder; outside of the ellipse is another friction roller, connected to the piston by compensation levers in such a manner that when the pistons are moving towards the cylinder, the rollers act on opposite sides of the ellipse, both pulling directly towards the centre, thus causing them to move forward on the ellipse, and communicating a rotary motion to the shaft. After the rollers have passed forward to the shortest diameter of the ellipse, the steam is exhausted from the ends of the cylinder and let into the middle, between the pistons, pressing them outward, causing the rollers in the ends of the piston rods to act on the inside of the ellipse, and coutinuing the forward motion of the shaft until they arrive at the long diameter, when the steam is exhausted from the middle of the cylinder, andis again applied at the ends. The results obtained were surprising, and can hardly be credited by helievers in the infallibility of the crank motion. The cylinder is about the size of the cylinder of an eight-horse crank engine, with a stroke of 3in. for each piston, and the power evolved was at least 22-horse power, and some present at the trial placed it as high as 25-horse power, with a speed of 100 revolutions per minue, and 501b of steam, consuming about the amount of fuel required for a 10horse engine.

THE PULSE.-Dr. Omanza describes a method of registering photographically, the beats of the pulse. The appartus essentially consists of a small inverted funnel, having a long narrow stem and a caoutchouc base. This instrument is filled with mercury to a certain distance and its base is applied to the heart or an artery; the oscillations of the mercurial column are then photographed by well-known processes. It is said that with this apparatus the apparently single stroke of the pulse is shown to consist of three, or even four, in succes sion.

and form,

He

DIMINUTION OF WEIGHT IN MAN DURING THE COLD MONTHIS.-Mr. Milner, of Wakefield (Am. Jour. of Med. Science), some years since performed a series of experimen ts with a view of determining the periodical fluctuations in weight, substance, which the whole body undergoes. weighed every prisoner upon his entrance into the convict establishment at Wakefield, and subsequently at the end of every calendar month, all of them being subjected to similar conditions of temperature, food, The number of men exercise, and ventilation. weighed exceeded 4000, and the total number of individual weighings was 44,004. From his experiments it was found that there was a progressive loss of weight in January, February, and March, and a gain in April, May, June, July, and August, and a loss in September, October, November, and December; or, in other words, an increase of weight during he hot These months, and a diminution during the cold. results are in accordance with physiological truth, for Dr. E. Smith has shown that the quantity of carbonic acid exhaled in winter is largely in excess of that given out in summer, and the sudden weight in April is found to correspond with an equally abrupt diminution in the quantity of carbonic acid expired.

UNIVERSAL STANDARD OF MEASURE MENT. According to the Memorial Diplum atique the Austrian Government has just signified its ass en to a proposal of the French Government for an International Commission to assemble in Paris in order to Already 15 European Powers agree upon a common standard of measurement for all civilised nations. have announced their willingness to take part in the commission. Even England, which hitherto has been disinclined to depart from old customs, will be represented by the Directors of the Observatories of Greenwich and Oxford. The French Government now only awaits replies from the United States, Brazil, and the South American Republics previously to calling together the commission. The Minister of Foreign Affairs would of right be the honorary president, but the proceedings will really be directed by the vicepresident, General Morin, Director of the Conservatoire des Arts et Metiers, in whose archives is deposited the official standard of the metre recognised in France.

ing the above company, established by operative watchmakers to promote the production of genuine London work. Mr. C. Young, who occupied the chair, opened the proceedings by declaring his conviction that the only way to retrieve the present depressed state of the trade, owing to the large importation of foreign watches duty free, was by the workmen combining together in a co-operative company to produce a watch equal in every respect to the best foreign watches imported, and at as low a price. There were three points upon which he believed there was no difference of opinion-viz., that if the watchmaking A CURIOUS DISCOVERY.-Dr. Milio, the celetrade was to be kept in this country, the whole system of production must be changed; that watches should brated surgeon of Kieff, has recently been at St. be of one uniform gauge; and that all foreign watches Petersburg explaining a means he has invented of sold in England should have the maker's name, and illuminating the body by means of the electric light to thus prevent them being palmed off on the public by such an extent that the working of the human machine may be observed, almost as if skin and flesh unprincipled sellers as English lever watches. The were transparent. The Moscow Gazette asserts that, meeting was then addressed by Mr. Ganney, who described the system of watchmaking by machiwery as to demonstrate the feasibility of his process, Dr. Milio placed a bullet inside his mouth and then lighted practised in America. It was acknowledged by all that the Clerkenwell watchmakers were the best work- up his face, upon which the bullet became distinctly [2575.]-GUTTA PERCHA v. ROPE BANDS.-Will men in the world, and the company were prepared to visible through his cheek. Dr. Milio does not propose any machine worker tell me which bands work best-supply a silver lever-plate watch, jewelled in four to lay bare all the secrets of the flesh, to explore the This watch had been designed and recesses of the heart, or to perform any miracles, phyutta percha or hemp rope, and which do their work holes, for 50s. sical or metaphysical. But he claims to have discovered best ? I believe rope is affected by the damp or dry produced by a committee, composed of the very best weather-I mean round bauds.-SUSSEX. a new and effective way of dealing with gun-shot workmen in every branch of the trade, and every part of the watch would be made in one building, thus wounds; first, by means of electric illumination he effecting a great saving in time and expense upon the discovers the precise situation of the bullet: next, by present system. Messrs. Newton, Holdsworth, Jones, means of magnetism, he proposes to extract the bullet Hislop, Mead, and others addressed the meeting in-provided always that the bullet contain some portion of steel. Against leaden bullets his system is powerless, and he therefore intends to represent to the were carried by large majorities:-"That in the International Committee, which lately met at Geneva, opinion of this meeting the union of labour and capital under a well-organised system of co-operation the desirability of recommending an admixture of is essential to the maintenance of the watch trade in steel in the manufacture of all future bullets. Dr. Milo's experiments with bullets containing only a That watches should be made by a Clerkenwell." said to have been uniform gauge, and that every watch should bear the slight admixture of steel are ་་ maker's name." "That this meeting pledges itself to thoroughly successful.

DARK.

[2576.]-PNEUMATIC PARADOX.- Could any of your ingenious readers give me an explanation of the

action of this little instrument?-SWANSEA.

[2577-BORING GLASS.-Can auy of my fellow-support of its objects, and the following resolutious readers inform me how to cut a hole, 2in. in diam., in the centre of a common piece of glass?-C. H.

[2578.]-CONTACT BREAKER.-Will "Tangent kindly say where I can purcase one of Rhumkorff's double quicksilver contact breakers, and at what price? Are they difficult to make?-THOMAS J O'CONNOR.

J. L. T.-Write to the Secretary of the Institute of Surveyors, APPLICATIONS FOR LETTERS PATENT DURING THE 12, Great George-street, Westminster.

The English Mechanic

AND

MIRROR OF SCIENCE AND ART.

FRIDAY, APRIL 29, 1870.

vious knowledge of them, of course failed to reap awakened interest in microscopy, and an inquiry the full benefit of the display; but those who as to the society represented, and other kindred were acquainted with the elements of natural ones in London. One thing should strike every history and microscopy, and who came to see and visitor to such a display as that of Wednesday not to be seen, found it possible to gain good re- night last-viz., the amount of freely offered sersults even in the heat, bustle, and jostling of the vice devoted to the getting up and successful crowd of fair and unfair visitors. The makers conduct of these soirées. Such service amply of microscopes were there, and had their tables proves the zeal of truly scientific men, and when richly garnished as aforetime, with burnished we learn that previous days of careful attention brass and glaring lamps. They showed, too, many are essential to the success of these exhibitions, THE ROYAL MICROSCOPICAL SOCIETY. highly attractive objects, but little or nothing we ought to be grateful to the officers and memnew to the advanced microscopist, though much bers of the Royal Microscopical Society, and to THE ANNUAL SOIREE. that was interesting to the passing gazer. But others on like occasions. May all these societies why should they make great efforts continually? find many new friends, ample funds, and a They have had their day, or their nights, and all thankful public to appreciate and applaud their the microscopic-loving world has admired their craft and landed their ingenuity.

ON
N Wednesday, the 20th inst., while nearly
all London was intent upon what it con-
ceived to be great things, a select company of
sage gentlemen were equally intent upon the
Amongst the objects shown by makers were
smallest of small things, in the precincts of King's some very fine sections of coal and coal-like fossil
College. At an early hour on that day the secre- wood. We noted also a particularly fine Podura
taries and chief members of the Royal Micro-scale, shown by Beck and Beck, and a few fine
scopical Society were at full preparatory work in objects under some instruments by Mr. Ross and
by Mr. Swift. The Society displayed a very good
their rooms. Cabs arrived every half-hour laden series of educational microscopes, with their
with microscopes, and the great savants were prices attached, and beginners would be delighted
hastening about, some with coats off, placing and to see such a series. The most straightened in
numbering the instruments. Several hundreds means may be comforted by such a show; for the
pounds' worth of microscopes arrived during the small outlay of three, four, or five guineas a
neat and useful little instrument may be had.
morning, and it was no slight proof of public
scientific spirit that all them were delivered and
located without difficulty and without expense.
Our own humble microscope gained its place
amidst a crowd of flaunting competitors which
were gloriously bright in highly polished brass,
and beautiful in appearance, but not a whit more
useful for all practical microscopic science. A
rich man may readily spend £120 with Mr.
Ross for a first-class instrument, but we are con-
fident that our own, at a cost of about £20, will
do as much and as good work, though less to look
at and lighter to move.

On this occasion, for the first time since its establishment, the Royal Microscopical Society attempted to inaugurate a new style of exhibition, Hitherto these displays have been of a very miscellaneous and heterogeneous character. The several makers of microscopes had seized the freely-accorded opportunity of showing their craft and skill to the great visiting public, and, in truth, the annual soirees have been theatres for the performances of Messrs. Ross, Smith and Beck, Powell and Lealand, Swift, Baker, Crouch, Murray and Heath, Stewart and Co., and other well-known makers. These soirees have really been manufacturers' bazaars, and greatly, it is understood, have they profited by them. During five or six of the latest of such displays the student will have observed many gradual improvements in the form and in the accessories of the instrument, and will have noted each step in advance in concurrence with the year of exhibition.

Still this was not fulfilling the highest purposes - of Microscopic science. It showed what was profitable, but not always what was scientific. To obtain results in the simplest and cheapest form is the desideratum of the student; to show them in the costlier form is perhaps that of the maker, not that the makers are without merit, for they have met the spirit of discovery and research nor can they be blamed if they also look for a tangible profit.

The Royal Microscopical Society has gradually gathered, by bequests and by purchase, a very considerable number of objects, chiefly indeed by gifts. The late Dr. Wallich, Mr. Richard Beck, and several others have given a most valuable series of objects to the Society, and the question has naturally arisen-bow, and when, shall these be exhibited? No occasion can be so good as the annual soirée. But, then, the instrument makers have nearly shut out the gentry of science. Well, let the gentry of science, for once, claim space with the makers; row such has really been the result. The Microscopical Society resolved to display its treasures, and never did they come to a worthier resolution. They printed a list of desirable objects, circulated it amongst the members, and thus contrived to offer a somewhat more systematic and really useful exhibition than aforetime. It was less showy to ladies, but far more instructive to men. For the first time, in fact, the soirée has been less miscellaneous, and more truly illustrative of particular classes of objects.

There was, indeed, no time for a leisurely study of the various objects, and those who had no pre

zeal!

COLOURS, AND COLOUR BLINDNESS.
BY "OMICRON."

IT is very evident to those who thoughtfully
consider the earth as the residence of man,
that the beneficent Creator has provided it not
only with the materials that are essential to the
existence of mankind, but He has provided much
that only contributes to his enjoyment. He has
not only considered the needful, He has con

sidered the beautiful. Enter the woods, and the

Dr. Carpenter was the lion of the evening, if the name of so large an animal is allowable' in ear is gratified by the songs of birds and the hum connexion with the smallest of creatures. On a of insects; the eye is pleased by the thousand raised platform at one end of the large room, he beauties of the landscape, and the variation of exhibited a very interesting series of objects from light and shade; all around is seen a tinted mass It is impossible to do any that speaks of the glory and goodness of the deep-sea dredgings. descriptive justice to them in a brief space-in fact, some considerable previous knowledge was Creator. And among the various examples of necessary to appreciate them at their true value. the care bestowed by Providence on man, one The wonder was not so much in the structure of of the most striking is the lovely mantle of colour a particular object as in its profound extraction. that is everywhere spread round about him; and To gaze at little spiudle-shaped "tests," or shell- yet what man has long and commonly enjoyed, like coverings, which were brought up from he often undervalues. To appreciate the full depths of 300, and 540, and 640 fathoms of sea-effect of this gorgeous robe of colour, it is neceswater, was no slight pleasure; while to examine sary to conceive a blind man suddenly restored them in connection with the useful little descrip- to sight. With what pleasure would he welcome tive catalogue printed by the Society, and also in this new sense! With what delight would he the clever enlarged drawings overhead, was full drink in this new source of enjoyment! With of instruction and entertainment. One object, a what interest would he survey the scene before small complete specimen of Orbitolites was most him, in its gay apparel! How long couldhe gaze attractive, for in it we studied the nucleus of the upon the far-reaching expanse of lively green disc formed by a spire of several turns, and the below him, and the calm deep azure above him approach to a cyclical arrangement, showing that without tiring of its loveliness. And after he had the whole subsequent growth takes its course on enjoyed the view of Nature in its marvellous a cyclical plan. Then there were a series of assemblage of tints and colours, with what Cristellaria, showing every gradation from the delight would he consider the details of the straight to the nautiloid form, which next to the seene, how tenderly he would touch the flowers, and, Globigerince and Orbuline are the most com- above all, how thankful would he be in the possesmon inhabitants of the abyssal waters. Beauti-sion of a sense which affords him such intense fully constructed are their finely-tubular shells, gratification! Very few value colour at its true while under another microscope was visible the animal itself of Cristellaria, which was obtained it, and consider other forms of beauty far preworth; and many often speak disparagingly of by dissolving the shell of a fresh specimen in ferable; and dilute acid.

human creatures living in a white world, they would soon feel what they owe to colour. The fact is, that of all God's gifts to the sight of man, colour is the holiest, the most divine, the most solemn."

many speak slightingly, because What could be a greater intellectual luxury sensitive to any kind of beauty. They really do not appreciate it, and are not "Such expresthan this bringing up, as it were, from the silent abyss of waters, some of its choicest and tiniest sions," says Mr. Ruskin, "are used for the most inhabitants, into the very heart of noisy and part in thoughtlessness, and if such disparagers populous London, and displaying them easily and of colour, would only take the pains to imagine pleasantly to the curious eye of every privileged what the world and their own existence would visitor to King's College on this Spring night? become if the blue were taken from the sky, and Here were some 1200 sightseers; many brought the gold from the sunshine, and the verdure from in commodious vehicles, all spared every kind of the leaves, and the crimson from the blood, drudgery and dredging labour, provided with fine which is the life of man, the flush from the cheek, instrumental aids to observation, in every respect the darkness from the eye, the radiance from the duly facilitated, and to crown all, with Dr. Car-hair-if they could but see for an instant white penter himself at hand, ready to answer any intelligent questioner, and sufficiently tolerant even of the bore and the bungler. In the upper rooms were the usual smaller displays, and relatively smaller, though by no means absolutely small, people of microscopic science. How pleasant on The investigation of the cause of colour has these occasions to meet old friends and ever to been attempted by several philosophers, though see old sights! On no account would we miss we can give here little more than the names of that amiable elderly enthusiast in polarised light, the more celebrated. Among the ancients, the who though literally one of the "nation of shop-hypotheses to account for the phenomenon of keepers," is a valued co-operator with the friends colour are sufficiently vague, and colour blindness, of his science. Ask him any question about or chromato-pseudopsis does not seem to have in polarised light, and you may count on a good and any way engaged their attention. With the useful reply. Long may we live in light! and Pythagorean school, colour was the superficies of and probably he would himself utter the prayer body; and Plato considered it as a flame issuing of one of the famous Homeric heroes, "Let me from bodies. Aristotle's notions were equally die in light,"-if we ventured to add one word to mysterious and inaccurate. After the long that prayer it would be "polarised." interval of the Dark Ages, when culture began to settle among the inhabitants of the West, modern philosophers promulgated their hypotheses. Des Cartes, the ingenious founder of the system of vortices, imagined colour to be a modification of light, and the difference of colour was produced by the rotatory motion of the particles that com

To the great, tumultuous, busy, or idle world of London, such sights as we have attempted to describe are unknown. Even the scientific world in other branches of study, scarcely know of their occurrence. Let us hope that the attention we have directed to them will bear fruits in a newly

cular colour, and to transmit or stifle, or as it is called in optics, absorb the others."

most intense purity, followed by a blue, which,
though at first its purity is affected by the green,
subsequently becomes of the purest indigo tinge, Mayer, in an essay "De Affinitale Colorum,"
though the illumination is more feeble than in objects to seven colours being received as
the yellow and earlier portions of the spectrum, primary, and regards all colours as being produced
and the luminosity is finally extinct in the violet from three primary ones, red, yellow, and blue,
rays. In experimenting on the ray of light it regarding white as a neutral mixture of rays of
should be as nearly as possible a mathematical all colours, and black as a mere negation of
ray. If the perforation be of about fin., and the white. Without departing from Mayer's doctrine,
distance from the screen to the prism, say, 18ft., any other three prismatic rays may be assumed
the spectrum will be 10in. long and 2in. wide, as the fundamental colours, for Dr. Young has
and show all the phenomena distinctly, and if the assumed red, green, and violet, and states as an
sun's rays can be collected by a lens of short focus experimental fact in support of this doctrine,
the purity of the colours will be much enhanced. that the perfect sensations of yellow and blue
Should the spectrum present the appearance we may be produced, the former by a mixture of red
have described, the experimenter may congratu- and green, and the latter by green and violet.*
late himself on being free from any strongly Mr. Hay, in his work on the Laws of Harmo-
marked form of chromato-pseudopsis, which is the nious Colouring," reports on some experiments he
expression that colour blindness is usually had attempted with three primary colours, and
known by in this country, and which means a he says "that he could not by analysis prove
false vision. On the Continent this peculiarity that there were only three colours, but that he
has received the appellation of Daltonism,* from sncceeded in proving it to his own satisfaction,
the celebrated John Dalton, the founder of the synthetically in the following manner :-After
Atomic theory, who suffered in a most marked having tried every colour in succession, and find-
degree from colour blindness, and who has de-ing that no one could be separated into two, I
scribed his own peculiarity with great care, in the next made a hole in the first screen in the centre
"Proceedings of the Manchester Philosophical of the blue of the spectrum, and another in that
Society," and has proposed a theory to account for of the red. I had by this means a spot of each
the phenomenon, of which we shall say more here- of these colours on the second screen; I then by
after.
means of another prism directed the blue spot to
the same part of the screen on which the red ap-
peared, where they united and produced violet,

posed light. From this date all the students of
physics connected colour with the phenomena of
light, accounting for it by the rays of light
entering the eye at different angles with the
optical axis. The experiments of Sir Isaac
Newton, however, began a new era in the history
of chromatics. By passing the solar ray through
a glass prism, it was plainly proved that light
was not homogeneous, but that it was composed
of a bundle of varied-coloured rays, some of
which were more refrangible than others. These
coloured rays were not capable of being sub-
divided into others; hence they were considered
primary, and the property of colour was supposed
to be occasioned by different substances reflecting
certain particular rays more copiously than
others. This theory was so simply deduced from
the observed facts, that it immediately obtained
universal belief, and all former theories died out
and were remembered only as matters of history.
Au object that appears white, reflects all the rays
indiscriminately, or does not sufficiently separate
them to make the distinction obvious, while a
body that appears black, absorbs, instead of
reflects, the rays that fall upon it. Simple as
this theory of Sir Isaac Newton's is, it must be
evident that it advances but a very little way
towards settling the troublesome question of dif-
ference of colour; for it still remains to be shown
why it is that certain bodies can reflect certain
rays more abundantly than others. Sir Isaac To return to our experiments on light and
attributes this effect to the density of the bodies. colour, and to completely establish the analysis of
He had observed while pressing together the sur-light, it will be necessary to form the solar rayas pure and intense as that of the spectrum. İ
faces of two prisms which were slightly curved, again in its integrity, from the many-coloured did the same with the blue and yellow, and pro-
that at the point of juncture the prisms were bands, in which it has been divided by the prism.duced the prismatie green, as also with the red
perfectly transparent, like one piece of glass; but It will be seen that the distance from the prism and yellow, and orange was the result. I tried in
that round that point appeared concentric rings to the screen, has nothing to do with the forma- the same manner to mix a simple with what I
of different colours, sensibly separated from each tion of the spectrum. However near the paper is called a compound colour, but they did not unite,
other. To make the experiment more completely brought to the prism, the spectrum is still visible, for no sooner was the red spot thrown upon the
and perfectly, he took the object glasses, one plano- though reduced in size, whence it necessarily fol- green than it disappeared. I tried the same expe-
convex, belonging to a 14ft. refracting telescope, lows that the ray has undergone division, imme- riment with two spectra, the one behind and of
and the other a large double convex, that belonged diately on leaving the prism. Let another prism course a little above the other, and passed a spot
to a telescope of 50ft. focal length. On bringing of a similar angle be placed in a reversed position of each colour successively over the spectrum,
the two object glasses into contact, the same (with reference to the first prism) very near the which was furthest from the window, and a similar
peculiarity manifested itself; at the point of con- first prism, and the ray of light will be perceived result occurred. It therefore appeared to me that
tact the two lenses appeared colourless, and this emitted in a direct line from the second prism, these three colours had an affinity to one another
spot was surrounded by a circle of blue, white unaltered and undeviated, as if no prism had that did not exist in the others, and that they
yellow, and red; the blue being small, and ap- intercepted the ray. To effect the confusion of could not be the same in other respects, except
parently possessing no trace of violet; the yellow the different coloured bands, a similarly con- colour and refrangibility, as had hitherto been
and red were far more prominent. This was structed prism is not indispensable, for a double taught."+
succeeded by another circuit, consisting of violet, convex lens employed in a similar manner equally
(To be continued.)
blue, green, yellow and red, all in about equal well effects the purpose.
proportions, excepting the green, which was less be produced by the assemblage of the entire
predominant than the other colours. The third pencil of rays, for if any portion be intercepted
circle was composed of purple, blue, green, yellow before it falls upon the lens, white light is not
and red. In this circle the green was more the result. If the violet end of the spectrum be
noticeable, and vied in brilliancy with any of the intercepted, the light will have a tinge of yellow,
other colours, except the yellow. The next and if the blue and green portion of the spectrum
circle was composed of green and red; the green be obstructed, the resulting combination of the Twiréseems to possess the property of tenacity
being very vivid. After this the colours grew other lines will be more and more red, till when
more and more faint, and incapable of being only the least refracted portion of the spectrum in the greatest, and leaden wire in the least
detected, till, after a few more bands of colour, is allowed to fall upon the screen, a brilliant red degree. The tenacity of cast iron is taken ad-
they finally terminated in complete whiteness. is the result. If the rays at the other end of the vantage of in the most scientific manner in the con-
Since the distance that the glass plates were spectrum-namely, the red extremity-be cut off, struction of the Britannia Tubular Bridge. It will
separated produced corresponding variations of the resulting light will pass through shades of be of some interest to those readers who do not
colour, Sir Isaac Newton concluded that colours green, blue green, blue, and at last, violet. By intend to study the subject in its details, to have
proceeded from the thickness of the plate of air intercepting intermediate portions of the spec-
intercepted between the glasses; that is, that the trum, the resulting light will exhibit every variety some particulars respecting this bridge, and for
different colours were transmitted or reflected of shade and colour that is to be met with in these the following is inserted :-The design of
according as the segment between the lenses nature. Now, if we consider that all these shades the bridge was made by the well-known engineer
was thicker or thinner; and the general law are produced on paper, which we usually term R. Stephenson, and forms one of the most wonder-
deduced by Sir Isaac Newton was, that the colour white, that is when exhibited to the full light of ful structures in the world. It spans the Menai
of all natural bodies depended on the density of the sun, and all the solar rays are equally re-
the body, or the size of the component particles. fracted, and that this same paper when placed in Straits on the line of the Chester and Holyhead
The experiment of the decomposition of light the red, green, or blue portion of the spectrum, Railway, within sight of Telford's chain suspen-
into its various component rays, is so simple and appears indifferently red, green, or blue, and that sion bridge, and was begun April 13, 1846,
beautiful, and, above all, so excellent a test for this phenomenon takes place whatever colour the completed, July 25, 1850, and opened for
colour blindness on the one hand, and a delicate body that receives the spectrum may appear in traffic, October 21, 1850; total cost, £601,865.
perception of colour on the other, that we trust white light, we are forced to conclude with It is made of cast iron, of a tubular form, in the
many of our readers may be induced to try it. Newton, that "the colours of natural bodies are
Let a prism be procured whose sides contain an not qualities inherent in the bodies themselves, tube of which the trains pass. Four of these
angle of about 55° (and the more perfect is the by which they immediately affect our sense, but tubes span the strait, two of which are 250ft.
prism, the more successful will be the experi- are consequences of that peculiar disposition of malleable iron in the tubes is 10.000 tons, of cast
and the other two 470ft. long. The weight of
ment), and held in such a manner that a ray of the particles of each body, by which it is enabled iron 1400 tons. In the middle of the strait is the
light may fall upon it from a small perforation in more copiously to reflect the rays of one parti-Britannia Rock, from which it has taken its
the shutter of a darkened room. The ray of light
name. The tubes are supported by piles of
will be refracted from its original direction, and
*In fact, scientific men have been sorely puzzled to
be bent upward; at some distance from the prism express the peculiarity generally known by the term high, and from the front to the end of the wing
suggest a convenient appellation that shall accurately masonry; that on the Anglesea side is 143ft. 6iu.
must be placed a sheet of paper, to receive the "colour blindness." Mr. Wheweil suggested" Idi-walls is 173ft. These wing walls terminate in
ray of light in its new course. On the screen pots" to designate the sufferers, which, however accu-
will be perceived an oblong spectrum containing receive any general favour, and Sir John Herschel tian character, and for each of these 2000 cubic
rate in its derivation, is too much like "Idiots" to pedestals, on which repose colossal lions of Egyp-
all the primary colours, at the bottom the least proposes Dichromic Vision" to mark the cause of feet of stone were required, each weighing 80
refracted colour, red, of a most brilliant tone, suffering. This term (as its derivation implies) sup-
more vivid than can be produced by any other poses that only two, and combinations of two colours tons, and being 250ft. 6in. long, 12ft. Gin. high,
can be seen by some eyes, while three, and combina-
means, or than any substance in nature presents. tions of three are visible to a normal eye. Mr. Pole, * Young's "Lectures on Natural Philosophy."
This dies away into an orange, which by insen- who describes with great care the affection of his eyes,
Ray" On the Laws of Harmonious Colouring."
sible degrees gives way to a pale straw colour, in the volume of the "Philosophical Transactions
for 1859," adopts this expression, and thinks it fully The right of reproduction is reserved by the
which in its turn is succeeded by a green of the explains his inability to detect certain colours.
Author.

White light can only

STRENGTH OF MATERIALS.‡
BY A. TOLHAUSEN, JUN.
(Continued from page 97.)

HE table given last week shows us that iron