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A CHAPTER ON SCIENCE AND ART.

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PLATE GLASS. — At the manufactory of St. Gobain, near Paris, a plate of glass has been lately cast, in a single piece, sixteen feet three inches in length, and eleven feet six inches in breadth. The ridiculously large mirrors of which we Americans are so fond, are all imported, and principally from England. The house of Chance and Co. send over a great deal annually, and find their account in so doing, notwithstanding the heavy duties exacted from them by the British government. Messrs. C. and Co. Pay a weekly duty of no less than five thousand pounds sterling.

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RAILWAY GATES. — We observe that a Mr. T. Lambert, of Stockton upon Tees, England, has invented an ingenious gate to be employed at the crossings of rail roads. This gate turns upon a central support, and is readily managed by one person. When open it prevents any one from passing on the road. It is furnished with an elevated circular signal, containing a lamp, which announces danger, at night. Its general effect tends to the protection of life and property at crossings, allowing at the same time the greatest possible facility for passing on the road.

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THE BOMB CANNON. — Experiments with Mr. Cochran's bomb cannon have lately been made at the Arsenal in Washington, and the efficacy of the invention satisfactorily tested. The first thirty-two discharges were made within four minutes. In another trial seventeen discharges were made in two minutes and twenty seconds — in a third, eight were made in a minute — in a fourth, three in the third of a minute. This cannon is readily managed by six men, while for ordinary guns eleven are required. The charge is introduced without either swab or ramrod. It can be fired at least eight times as fast as the common cannon. There is no recoil, and of course there is no necessity for breeching, and a hundred shots in quick succession do not produce inconvenient heat. These are the main advantages, but there are many others which we cannot here specify.

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VELOCITY OF CANNON BALLS. — It has been found by recent experiments that a thirteen-pounder, with an ordinary charge, impels its ball five hundred and six yards in the first second, and that, by increasing the load, it will send it eight hundred and seventeen yards in the same interval.

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MEDALS COPIED BY GALVANISM. — We spoke, in our last number, of Professor Jacobi's process for copying medals and engravings by galvanism. “The American Repertory of Arts, Sciences and Manufactures” (a very excellent periodical, whose publication has been lately commenced, at New York, by Professor J. J. Mapes) observes that several scientific gentlemen of that city have successfully repeated the experiments of Jacobi. The galvanic apparatus is very simple, and, by its aid, copper is precipitated from its solution as a sulphate, in a metallic form, upon the surface to be copied, making a perfect cast or impression. This discovery is of vast importance.

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IMPROVEMENTS IN THE DAGUERREOTYPE. — Mr. A. S. Wolcott, of New York, has nearly revolutionized the whole process of Daguerre and brought the photogenic art to high perfection. The inventor, it is well know, could not succeed in taking likenesses from the life, and, in fact, but few objects were perfectly represented by him, unless positively white, and in broad daylight. By means of a concave mirror, in place of the ordinary lens, Mr. W. has succeeded in taking miniatures from the living subject, with absolute exactness, and in a very short space of time.

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TRENCH’S PAPER MILL. — This is, perhaps, the most astonishing machine ever invented. By its means the common rags of the street are converted, in one process, and without leaving the mill, into a printed volume, cut into sheets and laid ready for the binder. Dr. Quin, in a late lecture upon the Mechanic Arts, at the New York Mechanics’ Institute, remarked very truly concerning Mr. Trench's invention, that a person might “throw in his shirt at one end and see it come out Robinson Crusoe at the other.” Mr. T. has deposited in the rooms of the Mechanics’ Institute a single sheet of paper containing six copies of Town's Spelling Book. He says that he can manufacture, if necessary, a single sheet one mile in length.

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THUNDER. — It is the opinion of M. Arago that thunder is never heard in the open sea, or in islands beyond seventy-five degrees of north latitude; and he thinks the same remark is applicable to continents. No reason is yet assigned. The opinion itself is based upon a variety of interesting researches.

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THE COMPRESSED AIR ENGINE. — We mention in our last a suppositious invention of a Mr. Bissell, of N. J., which professed to make use of condensed air as a motive power, and spoke incredulously of the attempt. It appeared obvious that no greater power could be obtained from compressed [page 247:] air than was employed in its compression, minus the friction of the compressing machine. However Mr. Bissell may think of getting over this radical difficulty, (one involving a leading principle of physics) still he can have no claim to be considered an inventor; for we find that the very same thing has been attempted, some time ago, by M. Houdin, and a patent of importation granted for it in Belgium.

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ANNUALS. — In the “Art Union, of Journal of Fine Arts,” it is stated that during the seventeen years in which annuals have been published in England, seven millions of dollars have been expended upon them. A table is given which shows that the engravers come in for the largest share of the spoil. The sums paid them precisely double those paid the poor authors. The binders come next after the authors.

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ÆROSTATION. — It is announced in the Parisian papers that M. Garnerin is fitting up a balloon at the Ecole Militaire which will accomplish the desideratum of navigating the air in any direction at the will of the æronaut. On each side of a boat (which serves for car) are placed four boards something like the sails of a windwill [[windmill]], which Mr. G. moves by the assistance of a machine in the interior, “the secret of which is known only to himself.” The resistance made by the air when struck by one of the boards “acts upon the balloon and carries it forward like a bird flying. Mr. Garnerin has already made several essays, which have been completely successful.”

This statement is nothing better than downright nonsense. It has been more than once demonstrated, a priori, that the control of a balloon in the manner here described is impossible. Among scientific men the idea ranks only with such projects as the quadrature of the circle, or the doctrine of perpetual motion. It is more than possible that the machinery here spoken of is the same as that of Mr. Green, the London æronaut, by means of which that ingenious gentleman proposes, not to direct the horizontal course of his balloon, but merely to regulate its elevation. It is composed o two fans, or blades of wood, attached to a spindle which passes through the bottom of the car. The fans are of one longitudinal piece, to the centre of which the spindle is fixed, in the fashion of a windmill, with but two winds or arms, their blades presenting a given angle horizontally, in which direction they move. A London paper describes the effect as follows.

“A miniature balloon of about three feet diameter, was filled with common coal gas; to this were attached the hoop, netting and car, and in the car a small piece of spring mechanism was placed, to give motion to the fans. The balloon was then balanced; that is, a sufficient weight was placed in the car to keep it suspended in the air, without the capacity to rise or inclination to sink. Mr. Green then touched a stop in the mechanism, which immediately communicated a rapid rotary motion to the fans, whereupon the machine rose steadily to the ceiling, form which it continued to rebound until the clock-work had run out. Deprived of this assistance, it immediately fell. The reverse of this experiment was then performed. The balloon was first raised into the air and then balanced. A similar motion was imparted to the fans, the action of which in this case was, however, reversed, and the balloon was immediately pulled down to the ground by their forces.

A more interesting effect still was then exhibited. The balloon, with the guide-rope attached to it, was balanced as before, the guide-rope having a small brass weight fixed to the end of it. The fans were then removed from under the car and placed sideways upon it, by which their action became vertical. Upon motion being communicated, the balloon floated in a horizontal line, dragging the guide-rope after it, with the weight trailing along the floor, and continued to do so until the mechanism ceased, when it immediately became stationary again. These experiments were frequently repeated with complete success.”

The guide-rope here mentioned is an invention very fully described, by Mr. Green himself, in the March number of the “Polytechnic Magazine.” It is another aid in the attempt at regulating elevation — a very material point. There are many causes continually in operation to exhaust the gas in an ascension — but none is more potent than the variation of distance from the earth. When the balloon gets up very high, into a rare stratum of atmosphere, the gas is excessively expanded and must be let off to prevent explosion. Meeting then with a cloud, the silk and cordage become saturated with moisture, and the whole machine falls with rapidity. Ballast must be thrown over — and to remedy this evil, is a very long cord, wound upon a windlass, and with several small buckets at its lower extremity, so contrived as to act either as floats, relieving the balloon of their weight by resting upon the sea, or as additional ballast by catching and retaining water. Mr. G. also gives an account of a drag by which his progress may be retarded while in the air. He speaks with entire confidence of the feasibility of crossing the Atlantic from America to Europe, and we have no doubt that he will shortly accomplish his design. He asserts that a current of air sets invariably from the north of west, at an elevation exceeding ten thousand feet — that in several hundred experiments he has never once found the case otherwise.