and three inches diameter throughout. I then took a dry fir straight-edge, twelve feet long, one inch thick, and four inches wide, which had been in use ten or twelve years, and was of course well seasoned, and on this I screwed two brackets, so as to feel that they touched each end of the ten feet shaft. When these dimensions were taken the thermometer in the shade stood at 14o. Reaum. (63° Fahr.) Last winter I had this shaft removed out of doors, and laid on two bricks, that it might be the more readily measured, and the frost have a better chance of acting on it. After the frost had set in some time, and when the thermometer was

140. Reaum.-making altogether a difference of 28 degrees-the contraction was one-tenth of an inch in the ten feet. I measured it again next morning, and found the contraction to be exactly the same.

Now, to have an idea of the practical importance of such a degree of contraction as this, we have but to consider that one-tenth of an inch in ten feet is equal to one inch in every 100 feet, or seven inches in an iron structure of the length of Southwark-bridge. Nor should the engineers of your country contemn such a source of danger from a notion that such a degree of cold as -14°. Reaum., is not likely to be experienced in the latitude of England. For in the winter of 1814, when the Thames was frozen over, and there was a fair held upon it, the degree of cold was fully equal to this.*

The iron shaft was again measured, when the cold had increased to 21o, and it was found to have shortened exactly one-eighth of an inch.

The cold here during the past winter has never exceeded 25°; but this is quite enough, since it is sufficient to reach both the water and gas pipes, and to cause immense inconvenience; for if such pipes are once frozen, it is of no use meddling with them till April or May. Even as late as July 4, the frost has been found in the ground four feet below the surface in particular situations. Coal gas condenses at 10 or 12 degrees of frost in out-door situations. A gentleman that has a large establishment in

*The thermometer in England has been observed as low as 2 deg. below zero of Fahr. scale, which is 151⁄2 deg. below the zero of Reaum. ED. M. M.

St. Petersburgh, lighted with coal gas told me that he had sad trouble with the lamps at a distance from the building. There are two gas lamps at the principal entrance to the factory where I am employed; the pipe is brought in a slanting downward direction inside the building, and a copper vessel is attached to it by a small cock and screw, to receive any of the gas that may be condensed; but though some condensed gas does find its way into this vessel, the cold is so intense that the pipe is at times frozen up with a solid body of ice to within a foot of the burner, which of course puts out the light. I have taken the copper vessel when thus filled with frozen gas, and put it on a slow fire, where as the liquid evaporated it burned with a yellowish blue flame, sufficient to show that it was hydrogen I am, dear sir, yours truly, WM. REED.

gas.

Peterhoff, Jan, 1834.

MARYLEBONE LITERARY AND SCIENTIFIC INSTITUTION.

Extract from the Quarterly Report, read to the Members, May 27, 1834.

"In the short period of one year from its establish ment on the present plan, the committee have been enabled to take premises more extensive and commodious than those of any similar institution in the metropolis. They possess already a library of 2,000 volumes, among which are many of the most valuable standard works in the English language, and a reading-room, supplied with ten daily papers, and every periodical work of merit. Classes for the instruction of members in mathematics, chemistry, botany, music, a nd the French language, have been formed; and lectures are regularly delivered by eminent professors, among whom areSir A. Carlisle, Dr. Lardner, Dr. Copland, Dr. Sou thwood Smith, Messrs. Hemming, John Taylor, Burnett, Wallis, and M'Culloch.

"The increase in the number of subscribers, during the past quarter, having been greater than that of any preceding quarter (135 new members having joined the institution during that period), induced the committee to make arrangements for a more commodious lecture-room. The negotiations which were then entered into for the purchase of addition al ground are now completed, and the erection of a theatre, capable of containing 850 persons, will immediately be com menced."

INQUIRIES.

Electrical Machines.-Sir, I have in my possession a piece of plate glass, out of which I wish to make an electrical plate machine; I have therefore to solicit, through the medium of your valuable Magazine, an answer from some of your numerous mechanical readers, to the following questions. Permit me to add, that I hope they will not for a moment hesitate in imparting to a young inquirer after knowledge, all that information which is essential to the production of a good electrical machine.

1. By what method can I convert an irregular sided piece of glass into a true circle?

2. How is the hole in the centre of the circle to be made; and by what means is the axis by which it is to be turned (when made) secured, so as to be able to turn the glass when four rubbers are pressing rather hard against it?

3. The thickness of the glass is about ths of an inch will this be a sufficient thickness? The utmost size that I can make it, will not be more than 13 inches diameter.

4. Will a machine of that size be powerful enough to perform all the common electrical experiments, such as firing gunpowder, spirits of wine, the thunder-house experiment, &c.? I am, &c. J. L.-B********, April 12, 1834.

Grinding and Polishing.-Sir, There is a piece of information which is very much wanted, and for which you may look in vain in the large Encyclopædias, namely, the mode of polishing by hand in the small way. I have an idea, that it is the powder of the substances themselves which is rubbed off in the process of grinding, that is employed to give the last exquisite polish; at any rate, it must be so with the diamond.--I am, &c. yours, G. DAKIN.-Dereham, March 3, 1834.

Optical Instruments.-Sir, Can any of your correspondents give me practical directions for constructing a Catadioptrical Phantasmagoria, of which a brief description is given in Dr. Brewster's Natural Magic? Supposing the diameter of the concave mirror to be 9 inches, and its surface nearly flat, I wish to know the size of the box or case, the size and focus of the lens for magnifying the objects, &c. &c.; I have been informed by an optician that the thing is altogether impracticable. I should also like to know what kind of an object glass I must procure for a magic lantern, the plane convex lens or bull-eye being 8 inches diameter and 10 in. focus-I am, &c. J. BATEMAN.

Weights and Measures.-Sir, Would you have the kindness to inquire, through the medium of your valuable Magazine, whether the weights in the town of Lincoln are the same as in the other parts of England, and how many pounds butchers' weight go to the stone? By so doing, you would oblige your constant reader, J. P.

Creaking Shoes.-Sir, I am a very nervous and irritable subject, and when employed in my study, am annoyed by the slightest disturbing circumstance, even a whistling wind, or a sudden crack in the furniture; but of all things the most obnoxious to me is the creaking of shoes or boots, either in a room or the street. If any of your readers can inform me of a preventive or remedy, they will confer an everlasting obligation on a real sufferer. I have had recourse to keeping the soles constantly damp, but this is liable to cause a cold by its effects on the feet, and also soon destroys the stitches.-I am, &c. S. S.-Gray's Inn, May 12, 1834.

Ascent of Smoke.-Sir, Is there any state of the atmosphere during which smoke will not ascend; and if so, what is that state, and how does it operate to prevent smoke from ascending? There are times when smoke seems to ascend much less readily than at others, and this I have heard attributed to the "heaviness" of the air. But surely this must be an error. Would not the smoke of a fire kindled on the top of a high mountain roll downwards instead of ascending; and that, not because the air in such a situation is heavier, but, on the contrary, because it is too light to afford the smoke the requisite support? If it were true that the denser the air, the greater is the difficulty in ascending in it, would not the same principle apply in the case of liquids, and might we not thence expect a cork or a ship to float more buoyantly in fresh water than in salt, contrary to the well-known fact. I trouble you with these queries from having more than once heard the remark made in London, that "the smoke does not ascend to-day, because the air is too heavy." The inhabitants of this city should know something of smoke; but if they are in error touching the cause of its not ascending, I trust that some of your ingenious correspondents will take the trouble to enlighten them. Ex fumo dare lucem, is, I hope, an object not unworthy of the "Mechanics' Magazine," even in a case of so little importance as the present.-Your obedient servant, Z.-April 22, 1834.

Sir,-A subscriber to the Mech. Mag., would be much obliged to any of its ingenious correspondents to inform him, how a square hole is to be filed by a round file?

B. T.

NOTES AND NOTICES.

An iron carriage, designed as well for heavy guns as for light field-pieces, has been constructed by order of Marshal Soult, under the direction of Captain Thierry, of the French artillery, and tried in the presence of the officers of that corps stationed at Nevers, when it met with their decided approval. It consists wholly of wrought iron, is much simpler in its construction than the wooden earriages at present used, and is of the same weight. The wheels are likewise of iron, of an elegant and peculiarly light make, cost less than any wooden wheels, and may be promptly repaired on the spot when injured. The avant train" is of the same material as the carriage, and bears a munition box of wrought iron, modelled on a similar principle to the vessels for water used in the French navy. An apparatus of greased leather encloses the box, and renders it impenetrable to moisture. By means of a mechanical power, derived from a simple iron lever, the carriage is arrested on the chassis, after its recoil, at a convenient distance for reloading. After this last operation, the mechanical check is removed, and the carriage descends to its proper position in battery by its own action, with a uniform motion, and without manual labour. Captain Thierry has also so arranged the construction of the chassis, which is made of iron, as without exposing it to too severe a strain, has enabled him. effectually to master the recoil of the piece, and within far narrower bounds than can be set in the

case of any wooden carriage. With a charge equal to one half of the weight of the ball, and after simply moistening the chassis, the recoil has never exceeded one metre and forty cents (55,200 inches).-United Service Journal.

1000

The House of Commons has, on the motion of Mr. Chas. Grant, appointed a Select Committee to inquire into the best means of promoting steam communication with India. The Messrs. Seaward, of the Canal Iron Works, in a pamphlet which they have recently published on this subject, recommend that vessels of very large capacity should be employed-of 1,600 tons, for example, with engines of 246-horse power. Such a vessel, they say, would allow of 900 tons being appropriated to merchandise, 100 to provisions and water, and 460 to coals-which last would suffice, with occasional assistance from the wind, to carry her to the Cape, where a further supply of fuel could be obtained. The time occupied in the voyage is calculated not to exceed eleven weeks.

"I perceive," says Kinclaven, "that Mr. Cheverton declines giving a solution to the question (see No. 562). He kindly informs me, that it Well, was a stale manoeuvre my proposing it.' well; if the readers of the Mech. Mag. should think so, then let it be so. Still I believe that most of them will agree with me that Mr. Cheverton himself has been guilty of a much staler manœuvre, in trying to act the part of the fox in the fable, by contemning that which (he knows right well) is far beyond his reach.' There are also some most unfounded statements in his last postscript, which I shall reply to in due time. For a short period I leave him to the tender mercies of his new female opponent, the highly-gifted M. S."

A printed paper has been sent to us, entitled, "A General Description of Proposed Improvements in London, projected by Mr. W. D. Holmes, C. E." We do not approve of all the author's suggestions, but there are two of them which we think extremely well deserving of consideration. The first is, that the Regent's Canal should be drained and converted into a railway, in which case it would form an extension of the Birmingham line, to the Thames, through one of the busiest

portions of the metropolis. The second is, to provide means for collecting, carrying away, and rendering available, as manure, the filth which now runs from the common sewers into the Thames" (a thing often proposed before). Mr. Holmes estimates that" the amount of manure now passed into the river and otherwise wasted, exceeds 12,000 tons per diem;" and that it "may almost, without expense, be concentrated to about 7,000 tons, which will yield a profit of 400,000l. per annum, áfter paying all expenses attending it.'

The Birmingham Musical Festival will take place, under the patronage of their Majesties, in the second week of October next. The spacious hall, in which the performances are to be held, is rapidly finishing; it will undoubtedly be one of the finest and best adapted rooms in Europe for the production of grand musical effects. The stupendous organ is also advancing towards completion. The hall, though of such dimensions as to be capable of holding nearly 8,000 persons, is so admirably constructed for the free transmission of sound, that it is believed the voice of a single speaker will be heard in any part of the vast area. -Cheltenham Chronicle.

Mr. Barton complains that Mr. Baddeley has misrepresented the actual construction of his metallic piston, in his communication of last week, respecting an alleged improvement of it by the Messrs. Heaton. He promises to send us, in time for insertion in our next Number, a paper in which this will be clearly demonstrated.

The contractors for executing the metropolitan end of the Birmingham railway, commenced operations on the morning of Wednesday last.

The completion of the beautiful new cut, by which the drainage of the Bedford Level has been rendered complete, and the Wisbeach river made navigable for vessels of 200 tons burthen, as far as the town of Wisbeach, was celebrated by a grand festival on the 23d ult. The plan was laid down by Mr. Rennie in 1824, and has been executed under the direction of Mr. Tycho Wing. It has cost about 200,000l.

SNOWDEN'S RACK-RA!LWAY.

The attention of the public has been earnestly invited, by a printed pamphlet, from the pen of John Ward, Esq.,* to the merits of a plan of railway conveyance patented several years ago by Mr. Snowden, the agricultural implementmaker, of Oxford-street, but hitherto treated (as is alleged) with most undeserved neglect. Mr. Ward asserts that "Mr. Snowden's admirable invention may be fearlessly put in competition with the most approved locomotive steam-engine and railway, and will far excel any thing hitherto produced, as well in respect to power and velocity as in regard to expense and actual outlay of capital." We shall first describe what these inventions are, and then inquire how far they justify the high opinion thus expressed of them.

The illustrative sketches which accompany this notice have been made up, partly from a personal examination of an experimental piece of railway, now exhibiting on Mr. Snowden's premises in Oxford-street, and partly from a drawing, furnished to us by Mr. Ward, of the description of carriage which, in his opinion, would be best adapted to such a railway, supposing manual power to be the motive force employed. Fig. 1 is a sectional elevation of the railway and carriage; fig. 2 an end elevation; fig. 3 a ground plan.

The railway is formed of two side-rails resting on suitable bearings, and properly braced together, with flat surface plates (LL), each three inches in width. Along the inner side of one of these rails, immediately under the surface-plate, runs a rack (K), into which a horizontal cogwheel (B), four feet six inches in diaméter, works. The shaft (A) of this cogwheel passes up through the centre of the working section of the carriage; and beneath it there is another wheel, but without cogs, attached loosely to the same shaft, which serves to keep the cogged one at the proper pitch-line. A second wheel (D), similar to C, is placed below the part of the carriage (1) intended to be appro

* A New Discovery, whereby Manual Labour can be most advantageously substituted for Steampower on Railways, &c. Being an Exposition of the Merits and National Importance of Mr. Snowden's Patent Improvements on Railways and Car riages. London: E. Wilson, 1834.

priated to passengers, in order to prevent the possibility of its slipping off the flat rails (LL). A winch (G), worked by men, who may be seated as in rowing, which is well known to be the most favourable position for the application of human strength, sets in motion two pulleys H H, which, by means of the wheel-work in connexion with them, impart rotation to the shaft (A), and thus propel the carriage. A fly-wheel (F), of the ordinary construction, is introduced to equalise the motion; and there are two guide rollers (E), which enable the carriage to adapt itself to whatever inequalities the line of railway may happen to present. wheels (as there is no flange to the rails) may be of any of the forms in common use in the accompanying engravings they are represented as of a conical shape, but that is probably the least advantageous that could be employed.

The

Mr. Snowden calculates that the entire weight of a locomotive apparatus, on this plan, with accommodation for sixteen passengers, besides the hands employed at the winch, would not exceed 18 cwt.

The particular grounds on which Mr. Ward rests its claims to superiority are these:

1. The employment of the rack-rail and cogged-wheel makes it (comparatively speaking) unimportant whether the railway is even or uneven; it may follow the natural inclination of the ground; and hence there will be “ no wasteful expenditure incurred for cutting down hills, or filling up hollow ground, to the required level." Mr. Snowden's inventions have accomplished what has been hitherto " unsuccessfully sought by the public, and in vain endeavoured to be achieved by scientific men." The expense of constructing the railway will be reduced, in short, to "little more than the cost of the iron," and of the ground required to be purchased.

2. The rails being flat at top, and without flanges, would oppose the least possible resistance to the progress of the carriage.

3. The first cost of the carriage—remembering always that manual power is to be the motive agent employed— "instead of being 1,000l., as is the case when steam is used, would not ex