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kept on the fire, one fluid ounce of water was introduced, and lasted about 115 seconds: 4 ounces lasted in one experiment, 294 seconds; and in another, 304 seconds; and the red heat was not kept up in the dish: the water was repelled at first.

18. In the copper bowl, No. VII., the thickness being .07 inch, or about .36 of that of the iron, the following results were obtained, the same tin bath being used, and the surface of the copper being smooth.

At a temperature of 4654°, one-eighth of a fluid ounce of water was repelled, the repulsion being perfect nearly to the close of the experiment. This quantity required 175 seconds to evaporate. At the initial temperature of 501°, the same quantity required 187 seconds to vaporise it. At the higher of these temperatures, in an iron bowl of nearly the same thickness, but in an oil bath, the maximum of vaporisation was not reached.

One-fourth of an ounce required 13 se conds to vaporise it at 469° Fah., and 405 seconds at 529°, at which latter temperature the repulsion was perfect nearly throughout the experiment.

Three-eighths of an ounce vaporised in 12 seconds, at the initial temperature of 471°, and the metal in contact with the dish was solid. At the initial temperature of 486°, the same quantity required 30 seconds, and the repulsion was perfect for 15 seconds.

Five-eighths of an ounce vaporised in 15 seconds, at the initial temperature of 481°, and also at 5091°. The minimum time of vaporisation being, probably, between these temperatures.

One ounce vaporised in 22 seconds, at 465, as the initial temperature; in 16 seconds, at 486°, and the tin was found congealed beneath the cup; in 17 seconds, at 511; the minimum time being probably between 486 and 5111.

Two ounces vaporised in 24 seconds, at 511, as the initial temperature; in 21 seconds at 526°, and in 22 seconds at 5564°; the minimum time of vaporisation being probably at or near 526° Fah.

From these results we see that between 471° and 486° Fah. 1,,, and 1 oz. vaporised in times differing but little from each other, the range being from 12 to 16 seconds; and that with two ounces, from 511° to 556°, the time of vaporisation was about four times the least of those just referred to. With quantities of water, varying from one-eighth of what the part of the bowl

which was in contact with the bath could contain, to one-half the capacity, the maximum vaporisation was between 471° and 481°, and 481°; and 511°, and the entire capacity of that part being filled, raised this temperature only to 526°.

This indicates the energy of the repulsion; for the evaporating surface being increased but about three times, and the water increased eight times, the initial temperature corresponding to the maximum of vaporisation was raised but '56°. It shows, further, that with metal at this temperature, eight times the volume of steam was formed in three times the time, when the entire capacity was filled and compared with one-sixteenth of this capacity filled; the quantity of 6121 cubic inches of steam, or nearly 3 cubic feet having been generated in 42 seconds, at the initial temperature of 526°, the steam having atmospheric pressure.

The copper, which was bright when the experiments were commenced, became oxidated as they progressed, thus tending to raise the temperature of maximum vaporisation.

Conclusions.

19. From the foregoing details may be deduced the following general conclusions, which will be found of practical import

ance.

1st. The vaporising power of copper, when supplied with heat, by a bad conductor or circulator, such as oil, increases with great regularity as the temperature increases, up to a certain point, the water being supposed thrown upon the copper surface in small quantities. Copper flues, heated by air passing through them, would be in this condition if left bare of water, and then suddenly wet. This holds with copper one-sixteenth of an inch thick, without indication that a limit will be attained by a much more considerable thickness. The temperature at which the metal will have the greatest vaporising power, is about 570° Fah., or about 233° below redness, according to Daniell.

The law of vaporisation of small quantities of water, by a given thickness of copper, is represented with singular closeness by an ellipse, of which the temperatures represent the abscissæ, and the times of vaporisation the difference between a constant quantity and the ordinates.

2. The same power in thin iron, 04 (32) inch thick, increased regularly, and was at a maximum, probably, at 510°. With thicker metal the power increases more rapidly at the lower temperatures, and varies very little,

comparatively, above 380°, with thicknesses exceeding one-eighth, and less than onefourth of an inch; attaining a maximum at about 507° Fah., when the quantities are small; rising to 559°, and much above, as the quantity of water is increased relatively to the surface of the metal which is exposed. Quadrupling the quantity of water, the entire amount being still small, nearly tripled the time of vaporisation at the maximum.

3. When copper of one-sixteenth of an inch in thickness was supplied with heat by melted tin, a worse conductor, and having a lower specific heat than copper itself, the time of vaporisation, in a spherical bowl, of quantities varying from one-sixteenth to onehalf of the entire capacity of the bowl, increased but three-fold, and the temperature of greatest evaporation was raised but 56°, or from 470° to 526°. When the bowl had half of the portion which was exposed to heat filled, the weight of the water was about one and one-tenth of that of the metal.

4th. The times of vaporisation of different quantities of water, varying from one-eighth of an ounce to two ounces, in an iron bowl one-fourth of an inch thick, and supplied with heat by the tin bath, were sensibly, as the square roots of the quantities, at the temperatures of maximum vaporisation for each quantity.

These temperatures were raised from about 460° to 600°, by increasing the weight of water about sixteen times, indicating that considerable quantities of water, thrown upon heated metal, will be most rapidly vaporised when the metal is at least 200° below a red heat.

5th. While a red heat, visible in daylight, given to a metal, even when very thick, and supplied by heat from a glowing charcoal fire, does not prevent water, when thrown in considerable quantities, from cooling it down so as to vaporise the water very rapidly, it is much above the temperature at which the water thrown upon the metal will be most rapidly evaporated. Thus one ounce of water was vaporised in 13 seconds, at about 550°, in a wrought-iron bowl one-fourth of an inch thick, and required 115 seconds to vaporise in a cast-iron bowl half an inch thick, at a red heat. Four ounces in the latter bowl vaporised in about 300 seconds, the bowl being red-hot when it was introduced; and two ounces vaporised in 34 seconds at 600° Fah.

6th. The temperature of greatest vaporisation, with a given thickness of metal, is lower in copper than in iron, the repulsive force

173

being developed at a lower temperature. With equal thicknesses of iron and copper, the vaporising power of the latter metal, at its maximum, was, with the oil bath, onethird greater than that of the former, and with the tin bath the power of copper 07 of an inch thick, was equal nearly to that of iron, one-fourth of an inch thick, each being taken at its maximum of vaporisation for the different quantities of fluid employed. As the maxima for the iron are higher than those for the copper, the advantage will be still greater in favour of copper when the two metals are at equal temperatures.

7. The general effect of roughness of surface is to raise the temperature at which the maximum vaporisation occurs, and to diminish the time of vaporisation of a given quantity of water at an assumed temperature below the maximum.

8. Though it has been shown that water thrown upon red-hot metal is adequate to produce explosive steam, even when it does not cool the metal down to the temperature of most rapid vaporisation, it is not the less true that metal more than 200° below a red heat, in the dark, is in the condition to produce even a more rapid vaporisation of water thrown upon it than when red-hot.

Stationary Temperature of Alcohol on heated Metals.

20. A curious fact was observed in regard to the temperature to which alcohol of the specific gravity 81, containing, therefore, 93 parts of absolute alcohol and 7 of water, could be raised in a heated dish. It is necessary, as an introductory remark, to recall the fact, that when the temperature of a liquid is gradually raised, by applying heat to the vessel containing it, a limit is reached when the temperature of the liquid becomes stationary, the vapour given out in boiling carrying off the heat which enters the mass. When alcohol, of the strength above stated, was projected into a bowl heated above the temperature at which repulsion of the fluid takes place, the temperature of the liquid did not rise to its boiling point. In fact, the stationary temperature, instead of corresponding with that of ebullition, was lower as the temperature of the dish was higher. This experiment was made in the course of attempting to infer the probable temperature at which water might be repelled from the more readily attained temperature of the repulsion of alcohol. Not being of direct application to the subject before us, it was not carried as far as in other hands it would deserve.

174

Sir,-As the mowing season is at hand, I hasten to lay before you a few hints on the subject of scythes. The common scythes are formed of a plate of steel, increasing in thickness from the edge towards the back, like most other cutting instruments. The consequence of this formation is, that as the blade wears away in breadth, through use and sharpening, its edge becomes thicker and thicker, till the angle is too obtuse for the purpose of cutting. Razors have the same defect; to remedy which, a French cutler, some thirty years ago, made their blades of a thin piece of steel of one uniform thickness, and then backed them with a rib riveted on like a tenanting saw. A patent has lately been taken out in this country for making scythes on a similar plan; I have seen and handled them, and find that they answer very well. But the mowers complain of these patent scythes being dear, as they cost from seven to ten shillings each. Very few mowers, I should think, having a common scythe already of their own, would feel disposed, or, if disposed, be able to throw it aside to buy a patent one, after the fashion of the French razor. By the use, however, of a very simple contrivance, the edge of the common scythe may be kept as thin as desired until it is entirely worn out; and which little expedient I wish to suggest through the medium of your excellent pub

lication; it is one that has been in use in Italy, time out of mind. Every mower in that country carries with him, conjointly with the whet stone, a little steel-faced hammer, and a little anvil. The hammer has a longish head, like those used for driv ing tacks, brads, &c. The anvil consists of a bar of iron, about one foot long. One end presenting a square surface of about an inch, faced with steel, and tapering to a point at the other end. At three or four inches below the

head, an iron disk, or a double looplike scroll, is welded on to the bar. The bar, or anvil, being driven into the ground (the hardest bit at hand) can enter no further than the disk. The scythe being then laid with its edge flat on the anvil head, is beaten with the little hammer, so as to reduce it to that degree of thinness, which the wear and sharpening is continually depriving it of An Italian mower performs this operation two or three times a day; and thys the blade is kept thin, and drawn out in breadth, for a long period of time. The anvil would, perhaps, be more conveniently portable, were the disk removable

from the bar. It might be of cast iron, about three inches diameter. A bit of stout sheet iron would be less liable to fracture.

I have the honour to be, Sir,
Your obedient humble servant,
F. MACERONI.

CIRCULATING DECIMALS.

Sir, Mr. A. Peacock is surprised that none of your mathematical contributors have taken notice of a certain question proposed by him in your 18th volume, respecting circulating decimals, &c. I am afraid that this neglect has arisen from your mathematical friends not attaching so much importance to the subject as Mr. Peacock imagined it deserved. In No. 661, he proposes the question:"Given 3488372+ a part of a decimal circulating series; required the whole of the series, and its equivalent vulgar frac

15 tion." Mr. Peacock finds that will

43

the question to finding a fraction that has the fewest possible figures, then in some cases the answer might be obtained by the rule he has given, when the decimal required to be produced is a pure circulate. But when the required decimal ("save the mark!") must be a mixed circulate, the method of continued fractions recommended by G. C. L. of Kentish-, town, gives a better chance of producing the vulgar fraction from which the deci mal is to be produced; but even in it there is no certainty, for I shall tell both gentlemen that I have two different vulgar fractions in my mind's eye, the first of which produces a pure circulate, and the second a mixed circulate, and that the first seven decimal places of both are 4256781. Could either gentleman tell me what were the fractions I had fixed upon? Certainly not. All that G. C. L. could do, would be to produce a series

175

of vulgar fractions that are alternately greater and less than the given decimal, and ultimately he would produce a vul. gar fraction exactly equal to the given The part of the fraction 4256781. probability of Mr. Peacock's finding the required vulgar fraction, would be in the ratio of infinity to unity. In all the calculations I have ever met with, we must take the decimals as we find them; some are finite, others recur, whilst others go on to infinity, following no regular law. Decimals, however, of this last order, Mr. Peacock does not recognise, or rather he is doubtful of their existence. However, if he will try to extract the square root of 2, or, what is the same thing, to find the diagonal of a square whose side is 1, he will find that although he should pursue the operation to as many places of decimals as there are particles of matter in the planet Jupiter, he would be as far from producing a circulating decimal as when he began. Well, then, if the ratio of the side of a square to its diagonal cannot be expressed in finite arithmetical terms, is there any thing extraordinary that this should also be the case with the diameter and circumference of a circle? Mr. Peacock still, however, fancies that the exact ratio of the diameter to its circumference may be obtained from some of the fanciful properties which he anticipates will be manifest when a better knowledge of circulating decimals is acquired! For his benefit, as well as all others whom it may concern, I shall give the following quotation from the writings of that eminent philosopher and mathematician, the late Sir John Leslie :

"The squaring of the circle is a problem which has at all times fascinated the attention and bewildered the reason of many superficial or antiquated students in geometry.

176

NOTES AND NOTICES.

at

Potatoe Beer.-A professor of chemistry Prague has succeeded in producing a very excellent kind of beer from potatoes, clear as wine, pleasant to the tasto, and strong.

A Walking-Stick, recently presented to Mr. Sopwith, surveyor, of this town, contains, in the dimensions of an ordinary cane, the following materials: Two inkstands, pens, pen-knife, ivory folder, Lucifer-matches, sealing wax and wafers, a wafer stamp, wax-taper, several sheets of post letter-paper and card-paper, a complete ar- highly finished set of drawing-instruments, ivory rule and scales, lead and hair pencils, Indian-rubber, Indian-ink, a thermometer, and a beautiful and wellpoised magnetic compass; the whole so arranged as to admit any instrument being used with facility. -Newcastle Paper.

New Carriage-Warmer.-Dr. M'Williams, of this city, has taken out a patent for a stove for heating carriages of all kinds, which is one of the most valuable inventions which has ever been made. It is remarkable in its structure, and may be sold for 6 or 8 dollars; and it consumes the most inconsiderable quantity of coal. The advantages of such a stove are almost too obvious to be mentioned. Taking up very little room, they may be fitted to the bottom of gigs or chaises, and of every variety of carriage, and are particularly well adapted to railroad cars. The expense of fuel is not above 3 cents for 100 miles travelling, at an ordinary rate. It is only necessary to make this invention known, to secure its introduction very generally. For a trifling expense, a stage-driver may now be as comfortably situated on his box, as by the by-room fire; and the pleasures of sleighriding may be enhanced a hundred fold. This stove is now used in the cars of the Baltimore and Washington Railroad, and gives entire satisfaction. The passengers are kept warm during the whole journey, and are never annoyed by smoke, the stove being air-tight.-Washington Mirror.

Ploughing by Steam.-Some experiments were lately tried at Red Moss, near Belton, in the presence of Mr. Handley, M. P. for Lincolnshire, Mr. Chapman, M. P. for Westmeath, and other gentlemen interested in agriculture, with a new and very powerful steain-plough, constructed by Mr. Heathcote, M. P. for Tiverton. About 6 acres of raw moss were turned up in a few hours, in the most extraordinary style,-sods 18 inches in breadth, and 9 inches in thickness, being cut from the furrow, and completely reversed in position, the upper sur face of the sod being placed exactly where the lower surface had been before. *** The plough of Mr. Heathcote, though a very powerful machine, appears to us to be much too complex and costly for common agricultural purposes; though we have little doubt that it might be used not only with effect, but with advantage, in reclaiming large portions of moss land, such, for instance, as the bogs of Ireland. Indeed, it is the opinion of Mr. Heathcote himself, that it would not at present answer to employ it in reclaiming a smaller portion of bog than 1,500 or 2,000 acres, though it may probably be cheapened and simplified so as to make it ultimately useful on a smaller scale.-Liverpool Paper.

Railroads in the United States.-It is estimated, on good authority, that at this time the railroads in the United States, either actually under contract or in progress of being surveyed, amount to more than 3,000 miles. Each yard of the highest iron rails, fit for a railroad, weighs 624lbs. As there are 1,760 yards in a mile, each mile of railroad, with a double track, will require 238 tons of rails, besides chains, screws, and bolts-amounting, in the whole, to at least 250 tons of iren per mile-250, multiplied by 3,000, is 750,000 tons of iron, that will

shortly be used in the United States in the construction of railroads. Such is the demand for railroad iron in England for the American market, that common bar-iron, which one year ago was worth only 67. 108. sterling in Wales, is now worth 97. 10s. at the Weish works, as appers by the British Prices Current. It is stated in the New York papers, tht at this time contracts have been ac tually made in England, by American houses, for 400,000 tons of railroad iron to be shipped to this country.-9. 10s. sterling is about 45 dollars of our money; but railroad-iron costs more than common bar-iron, and is at this time worth at least 50 dollars per ton, at the works in Wales or Staffordshire. Four hundred thousand tons of iron, at 50 dollars per ton, is twenty millions of dollars, that the people of the United States are bound to pay to the English by their present contracts for railroad-iron. If all the projected railroads of this country shall be laid down with British iron rails, we shall pay to the English nation, within the next seven years, at least fifty millions of dollars for railroad-iron. And yet we have in our mountains both iron ore and coa', of the best quality, and in quantities sufficient te yield iron for the whole world.-American Railroad Journal. - [Another interesting article on this subject will be found in a preceding page.-ED. M.M.1

Introduction of Burden's Boat into France.Baron Seguier, Member of the Institute, has constructed a boat after the plan of Burden's, of two double cones, 100 feet long, with the engine between them, which, with the boiler, presents some improvements. M. Cave, a mechanical engineer, has also constructed a double boat, for the navigation of the canal of Somme. It differs from the preceding in being open at the surface, covered with a flooring, and has two keels and two helms. A similar boat has been constructed for the navigation of the Loire, between Nantes and Angers, -Bul. Soc. Enc. l'Ind. Nat.

As we

J. H. labours under a popular error. have before mentioned, there is no reward offered for the discovery of perpetual motion.

Mr. Henderson's paper is left with our pub. lisher for him.

Communications received from Mr. EtrickCampo bello-Zeta-Mr. J. Wilbee.

The Supplement to Vol. XXIV., containing Ti tle, Contents, Index, &c., and embellished with a Portrait of Mr. Walter Hancock, C. E., is now published, price 6d. Also the Volume complete in boards, price 98. 6d.

British and Foreign Patents taken out with economy and despatch; Specifications, Dis. claimers, and Amendments, prepared or revised; Caveats entered; and generally every Branch of Patent Business promptly transacted. Drawings of Machinery also executed by skilful assistants, on the shortest notice.

LONDON: Published by J. CUNNINGHAM, at the Mechanics' Magazine Office, No. 6, Peterborough-court, between 135 and 136, Fleet-street. Agent for the American Edition, Mr. O. RICH, 12, Red Lion-square. Sold by G. W. M. R«YNOLDS, Proprietor of the French, English, and American Library, 55, Rue Neuve, Saint Augustin, Paris.

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Fleet-street.