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quaintance among philosophers, and the intelligent manufacturers of these kingdoms, that the latter requisites will appear sufficient to render his journal interesting even to the few who are so fortunate as to have access to all the expanded sources of philosophical intelligence : but, at the same time, he insists on the observation that those sources, namely the academical transactions, and the mutual communications of men of ability, under all the dificulties of price, distance of publication, difference of language, multiplicity of perusal, and the efforts of mental abridgment, must continue unknown to a very large class of men of science. He declines entering into any absolute promises, either with regard to the ability or the integrity proposed to be shewn in his undertaking, or to the specific ineans by which he hopes to merit the public approval. It appears to him more natural and easy, to leave every indi. vidual of principle and understanding to imagine what ought to be done ; and he observes that the duties hereafter to be exercised will present themselves in the regular course of events, and leave no cause for hesitation.

In the latter advertisement, written after the completion of the forst volume, Mr. N. expresses his satisfaction that his work has afforded him the friendship and correspondence of men whose virtues and talents he reveres. He points out to the public, that nearly half of the papers in his volume are original and interesting ; that above one third relate to new and important works, which have never yet appeared in our language; and that the remaining part consists either of digested reports and abridgments of excellent but voluminous papers, dispersed in academical collections, or of such as from other circumstances deserved to be copied entire.

We will now consider some of the contents of this useful publication ; slightly passing over or omitting such as we may have had occasion to notice in the other departments of our undertaking, and dwelling more particularly on such as are either entirely original or uncommonly interesting.

The Principles and Application of a new Method of constructing achromatic Telescopes. By Robert Blair, M. D. This paper is an abridgment of the Doctor's account inserted in the third (Mr. N. has by mistake said second) volume of the Edinburgh transactions, and was analysed at some length in our xixth vol.N.S. p. 246 & seq. We scarcely need to remind our philosophic readers, that this invention consists in the use of one or more fuid mediums, of which the dispersive powers, being opposed to each other, not only correct the focal irregularities of the extreme rays of the Newtonian spectrum, but likewise those near the middle; to which, former opticians had little if at all atRev. JULY, 1799.

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tended. It would give us pleasure, if we could announce the progress or complete practical application of this ingenious theory. Whether it be, that the fluids are subject to alteration from chemical agency or mechanical subsidence; or to the circulations from heat to which Count Rumford has so lately directed the attention of the world; or from whatever other cause it may have arisen ; the fact undoubtedly is, that the inventor some years ago took out a patent for these telescopes; and that some of them, of small dimensions, but of considerable aperture and accuracy, were put into the hands of a few artists in this capital, since which time the subject has remained dormant. : A remarkable Effect of the Inflection of Light passing through Wire Cloth, not get clearly explained. Mr. N. relates, from Mr. Rittenhouse's paper, in the second volume of the transactions of the American Philosophical Society, a fact which presents itself on looking through a fine muslin handkerchief, or wire cloth, at a distant light. The light seems multiplied, and the images are arranged in a certain regular order. This phænomenon appears to much greater advantage, if the cloth be stretched over the object-glass of any telescope or small perspective. Mr. Rittenhouse ascribed the event to inflection. On repeating and varying the experiment, Mr. N. obtained a solar spectrum of uncommon beauty, of which he has given an engraving. He has detected several mistakes of Mr. Rittenhouse, and he proposes a theory in some respects different, but which, he himself owns, is liable to objections. Description of an Instrument which renders the Electricity of the Atmosphere and other work Changes very perceptible, without the Possibility of an equivocal Result. This instrument was invented by Mr. Nicholson in the year 1787, but has not been before described. It will not be easy for us to convey a clear notion of its parts without the engraving.

Observations on the Art of printing Books and piece Goods by the Action of Cylinders. Mr. N. has here given the results of much experience, in an art on which many thousands of pounds have been speculated in this country with no very great success. It is well known that copper-plate engravings are impressed by the successive action of a pair of cylinders, and that books and block-impressions are printed by the action of a flat surface urged by a screw against the original type. Many very evident advantages offer themselves in favor of the rotatory process of impression from an engraved cylinder; the chief of which are that the fittings in piece goods are precisely accurate, and that the unintermitted speed may reasonably be expected to afford

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a great saving of labour. Whether the difficulties of printing with a variety of colours, which require successive trausitions of the stuff through different niachines, and of preventing the piece from departing out of the immediate direction which it is intended to follow, be insurmountable, or may demand a different method of treatment from any which has yet been used, does not appear. The present memoir however affords many important circumstances of information, and deserves to be consulted by every inventor who may propose to follow this investigation.

New Method of Tanning. By Mr. William Desmond. - Mr. D. has taken out a patent for Seguin's method of tanning. The present article is simply a description of the process. The French chemists, taking up the experiments of M. de St. Réal which appeared in the Turin Memoirs, have observed that the aqueous infusion of astringent substances consists chiefly of two distinct and active substances ;---the tanning principle, of which the most prominent charac!er is that it combines with glue and forms an insoluble precipitate,-and the acid of galls, well known for its atramentous combination with iron. They have ascertained that the fibrous matter of animals becomes converted into jelly by oxygenation ; and that, in the process of tanning, this oxygenated fibrous matter is gradually rendered insoluble by combination with the tanning principle, so as to preserve its organised form and flexibility in the new compound, which is leather. Reasoning from these facts, or rather (as it may be imagined) acting first and reasoning after. ward, they have advanced the doctrine that leather, instead of requiring the deposit of a capital in the tan pit for eighteen months, may be made as speedily as the due processes of oxygenation and absorption of the tanning principle can be brought about ; that is to say, in the course of a few days. Mr. Nicholson, whose duty as the journalist did not permit him to allow these theoretical positions without previous inquiry in the market, obtained additional information on the subject from respectable manufacturers in that branch, which tends to throw considerable light on the invention. To this we will also add that, though the new process appears to be scientific and very ingenious, it nevertheless seems to call for farther improvements, before it can supersede the present method ; and that we do not apprehend that Mr. Desmond has yet opened any warehouse for the sale of his new product.

Description and Account of a new Press operating by the Action of Water, upon the Principle of the Hydrostatic Paradox. By Joseph Bramah.—This invention consists of two metallic pipes or cylinders; a large one and a smaller. In the larger cylinder,

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slides a solid piston ; and the smaller is fitted up as a forcing pump to drive water beneath the piston of the larger. The ascent of this last is applied in works of compression, instead of the screw in the common press. The diameters of the two pistons being known, together with the pressure on that of the small pump, it is easy to compute the action by which the larger piston rises ; for they are as the surfaces. The advantage of Mr. Bramah's press beyond that of the screw consists in its having less friction. In a press which Mr. Nicholson saw, a piston of four inches diameter was raised by one man with considerable speed, under the action of 47040 pounds, or 245 atmospheres. We are disposed to think that the principal difficulty, in the practice of this invention, will consist in keeping all the parts sound and tight under such enor. mous pressures.

On the Hydrometer of Baumé. The French chemists continually speak of acids and alcohol as possessing certain num. bers of degrees of strength, which degrees are intended to be of the hydrometer of Baumé : but, as this instrument was never used except in France, it appeared a desirable object to reduce its numbers to the common expression of the tables of specific gravities. Mr. Nicholson has accordingly made the computations, and has given an account of the elements on which he has grounded his results.

On the Methods of obviating the Effects of Heat and Cold on Time-pieces. Mr. Nicholson has here given a popular account of machines to measure time, particularly the regulating parts; which are the fly, the balance, and the pendulum. He ex. plains the various combinations of metals for this purpose by Graham, Ellicott, and Harrison, with the more modern con trivance of the expansion balance; which operates by the flexure of two bars of brass and steel soldered together. He explains the principle of this action, and gives a description of an original application of it to a pendulum of his own, with instructions to workmen.

Observations and Experiments on the Light, Expence, and Construction of Lamps and Candles, and the Probability of rendering Tallow a Substitute for Hax. This is an interesting original paper. The author treats of the admeasurement of the intensities of light, the construction of lamps, and the difference between lamps and candles; which last principally consists in the elevated temperature of the point of congelation in the fat oil of the latter. Common oils are habitually fluid. Tallow melts at 929 Fahrenheit, Spermaceti at 133°; the fatty matter formed of flesh, after long immersion in water, melts at 127o;

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the Pela of the Chinese at 145°, Bee's wax at 142°, and bleached wax at 155o. From several ingenious and obvious considerations, Mr. N. shews that the tallow candle is inferior to that of wax in no respect but the greater fusibility of its material, which forms a more perishable cup at the upper extremity, over which the tallow would run down, if the wick were not made larger than in the wax candle. The thin wick of the latter being unable to support its own weight, when of considerable length, it turns on one side, and undergoes a complete combustion from the contact of the air : but the thicker wick of the tallow candle, instead of bending, remains in the centre of the flame, impeding the combustion, and diminishing the quantity of light by a loss of nine tenths of the whole in the extreme case; and it can only be made to operate with effect by frequent snuffing. Various experiments, mechanical as well as chemical, are related to obviate this imperfection. None of them are sufficiently effectual to render the tallow candle equal to that of wax: but the paths of investigation to which they lead are promising, and the subject well deserves to be pursued.

Account of the Magnetic Polarity of a Mountain of Serpentine. By M. Humboldt. The manuscript account of this singular magnetic mountain, situated in the Margraviate of Bareuth, was communicated to the editor by Sir Joseph Banks. It is an isolated hill, rising to the elevation of fifty toises above the surrounding plain, and extending in length from west to east. covered rocks on the northern slope exhibit south poles, and those on the declivity towards the south have north poles. The whole mass does not possess a single magnetical axis, but presents an infinity of different axes, perfectly parallel to each other and to the line of magnetical direction of the earth; though in the contrary position. It therefore reverses the position of the needle of the mariner's compass, when brought near to it. The east and western slopes, though in no external respect differing from the rest, do not affect the needle.-For other particulars, we must refer to the paper itself.

Sir Joseph Banks also presented Mr.N. with a piece of the rock, of which he has added the mineralogical description, together with an account of some experiments. The most remarkable character mentioned by M. Humboldt is, that this stone, though it possesses a strong magnetic polarity, has no attraction for iron filings. Mr. Nicholson could not satisfy himself that it does in fact possess this last property : but he questions whether a natural magnet, as weak in directive power as this stone, might not have been equally inactive with regard to iron filings.

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