brought the difficult subject of the metallurgy of magnesium to its present very satisfactory position. Some fine specimens of crude and distilled magnesium weighing 3 lbs. were exhibited as manufactured by Mr. Sonstadt's process, by Messrs. Mellor & Co. of Manchester. * The wire is now to be had at the comparatively low rate of 3d. per foot; and half-an-inch of the wire evolves on burning light enough to transfer a positive image to a dry collodion plate; whilst by the combustion of 10 grains a perfect photographic portrait may be taken, so that the speaker believed that for photographic purposes alone the magnesium light will prove most important. The photochemical power of the light was illustrated by taking a portrait during the discourse. In doing this the speaker was aided by Mr. Brothers, photographer, of Manchester, who was the first to use the light for portraiture. [H. E. R.] GENERAL MONTHLY MEETING, Monday, May 9, 1864. WILLIAM POLE, Esq. M.A. F.R.S. Treasurer and Vice-President, in the Chair. The Hon. Henry Frederick Cowper, George Clive, Esq. M.P. Lieut.-Col. George Palmer Evelyn, William Graham, Esq. were elected Members of the Royal Institution. : The following Professors were re-elected : WILLIAM THOMAS BRANDE, Esq. D.C.L. F.R.S. Hon. Professor of Chemistry: JOHN TYNDALL, ESQ. Professor of Natural Philosophy; EDWARD FRANKLAND, ESQ. Ph. D. F.R.S. Professor of Chemistry. The Secretary announced the following additions to "The Donation Fund for the Promotion of Experimental Researches" (see page 151). * From Messrs. Johnson and Matthey of Hatton Garden. A REPORT was read from the Committee of Managers, dated 18th April last, which stated, in effect, that such part of 22 Albemarle Street, as belonged to the Royal Institution would, on the termination of the lease thereof subsisting when originally purchased by the Institution, fall in to the Institution in June, 1870; and that an integral part of that house, together with the court-yard at the back of it, both essential to the convenient occupation of the Institution's part, did not belong to the Institution, but to a family of the name of Baldry, and that this Baldry part came to be sold by auction early in that month of April, and the great depreciation that would arise to the Institution's part of 22 Albemarle Street if this Baldry part should be purchased by anyone else; and that this Baldry part being held by the Baldrys under one lease with the adjoining house, 166, New Bond Street, was to be sold with that house in one lot, and that if purchased for the Institution, the Managers had arranged with a responsible tenant to take a lease until Michaelmas, 1891, of the whole of this Baldry property, at a rent which would return to the Institution a clear 41. per cent. per annum on the purchase-money; and that under these circumstances the Managers had sanctioned the purchase of all this Baldry property at the auction for 7,900l. The Report concluded by strongly recommending to the General Meeting of Members to pass a Resolution in conformity with the Notice which had been sent to the Members, pursuant to Chap. XI., Art. 1, of the Bye-Laws, for authorizing the sale of sufficient of the consols in the name of the Institution for completing the purchase. The Meeting thereupon passed a Resolution approving of the abovementioned Report, and authorizing the Sale of Stock, in conformity with the Notice which had been sent to the Members, as mentioned in that Report. The PRESENTS received since the last Meeting were laid on the table, and the thanks of the Members returned for the same: viz. FROM Governor-General of India-Memoirs of the Geological Survey of India :— Actuaries, Institute of-Assurance Magazine. No. 55. 8vo. 1864. Astronomical Society, Royal-Monthly Notices, 1863-4. No. 5. Beke, Doctor C. T. (the Author-On the Sources of the Nile. (L14) 8vo. 1864. Chemical Society-Journal for April, 1864. Editors-Artizan for April, 1864. 4to. Athenæum for April, 1864. 4to. Chemical News for April, 1864. 4to. 8vo. Engineer for April, 1864. fol. Medical Circular for April, 1864. 8vo. Practical Mechanics' Journal for April, 1864. 4to. Technologist for April, 1864. 8vo. Franklin Institute of Pennsylvania-Journal, Nos. 458-459. Faraday, Professor, D.C.L., F.R.S.-Memorie della Reale Accademia delle Scienze di Torino. Seconda Serie. Tomo XX. 4to. 1863. Geological Survey of Canada :-1843-63. 8vo. 1863 Industrial Resources of the Tyne, Wear, and Tees. 8vo. 1864. Genève, Société de Physique de-Mémoires. Tome XVII. Partie 1. 4to. 1863. Geographical Society, Royal-Proceedings, Vol. VIII. No. 3. 8vo. 1864. Geological Institute, Vienna-Jahrbuch. No. 2. 8vo. 1863-4. Gilliss, Captain, J. M., U.S.N. (the Superintendent)-Astronomical and Meteorological Observations at the Observatory at Washington in 1862. 4to. Horticultural Society, Royal-Proceedings, 1864. No. 6. 8vo. Liverpool Athenæum-Classified Catalogue of the Library. 8vo. 1864. 1863. Mechanical Engineers' Institution, Birmingham-Proceedings, August. 8vo. 1863. Newton, Messrs.-London Journal (New Series) for April, 1862. 8vo. Newton, A. V. Esq. (the Author)-On the Patent Laws. (L 14) 8vo. 1864. Petermann, A. Esq. (the Editor) —Mittheilungen auf der Gesammtgebiete der Geographie. 1864. No. 2. 4to. Photographic Society-Journal, No. 144. 8vo. 1864. Royal Society of London-Proceedings, No. 62. 8vo. 1864. R. C. Carrington: Observations of the Spots of the Sun, 1853-61. 4to. 1863. Roma, Accademia Pontificia de' Nuovi Lincei-Atti: Anno VII. (1854.) Sess. 3, 4, 5. Anno XIV. (1861.) Sess. 3-7. Anno XV. (1862.) Sess. 1-8. Anno XVI. (1863.) Sess. 1-5. 4to. Silliman, Professor S. (the Editor) — American Journal of Science. Second Series. No. 110. 8vo. 1864. Sundys, Sampson, Esq. (the Author)—On National Defence, &c. (K 90) 8vo. 1864. Taylor, Rev. William, F.R.S. M.RI.-W. Strange: The Seven Sources of Health. 16to. 1864. Toronto University-Abstracts of Magnetical Observations at Toronto, 1853-62. 8vo. 1863. Volpicelli, Professor P. (the Author)-Sulla Elettrostatica Induzione. 4to. 1863. WEEKLY EVENING MEETING, Friday, May 13, 1864. MAJOR-GEN. Edw. Sabine, R.A. President R.S. Vice-President R.I. in the Chair. JOHN SCOTT RUSSELL, C.E. F.R.S. On the Mechanical Nature and Uses of Gun-cotton.* GUN-COTTON is a new power coming under the same category as steam and gunpowder. It is highly dangerous to those who do not For the Chemical History of Gun-Cotton, see Mr. Abel's discourse, p. 245 of this volume. possess the necessary knowledge and skill; but, like them, it enormously extends human power, and like them, the skill to use it can be rightly and certainly acquired. I. Is gun-cotton stronger than gunpowder? The answer to this is, Yes, sixfold stronger. By this we mean that if we take a given weight of gun-cotton, say four ounces, if we bore a hole 1 inch in diameter and 3 feet deep, into hard rock or slate, in a quarry, and put 4 ounces of gun-cotton into it, it will occupy about 1 foot of its length, and the aperture being closed in the usual manner, and a match-line led from the charge to the proper distance from which to fire it; and if we next take 24 ounces of best gunpowder, bore a similar hole, and charge it similarly with gunpowder, and close it in the same way; it has been found that, on these being exploded, the 4 ounces of gun-cotton have produced greater effect, in separating the rock into pieces, than the 24 ounces of gunpowder. The answer is, therefore, that in disruptive explosion the strength of gun-cotton is sixfold that of good gunpowder. But the disruptive or bursting power of gunpowder is not always the quality for which we value it most, nor the service we require of it. In mining rocks, in exploding shells, in blowing up fortresses, this property is what we value, and this work is what we require. But we do not want to burst our fowling-pieces, our rifles, our cannon. On the contrary, we want to use a force that shall project the projectile out of the gun without bursting the gun, without straining the gun beyond a given moderate limit, which it shall be able to endure. We want therefore a service from gun-cotton which shall be the contrary of destructive to, or disruptive of, the chamber in which it does the work of giving motion to the projectile. This moderated and modified work, gun-cotton can also perform ; and it is the modern discovery of General Lenk, which has enabled us to moderate and modify gun-cotton, to this gentler service. He discovered how to organize, arrange, and dispose mechanically of guncotton in such a way that it should be three times stronger than gunpowder. Accordingly, one of his charges of gun-cotton, weighing 16 ounces, projected a 12-pound solid round shot with a speed of 1,426 feet a second, while a charge of gunpowder of 49 ounces gave the same shot a speed of 1,400 feet a second. One-third of the weight of gun-cotton exceeded, therefore, the threefold weight of gunpowder in useful effect. II. Is gun-cotton more convenient than gunpowder? This is a larger and more various question than the former, and divides itself into various subdivisions. It is well known to sportsmen, to soldiers, to artillery-men, that gunpowder fouls a gun. A foul residue of soot, sulphur, and potash soils the inside of the gun after every charge. The gun must, somehow, be cleaned after a discharge; if not it fires worse, recoils more, and ceases to do its best. If the gun be a breech-loading gun its mechanism is dirtied, and works less easily. Gun-cotton deposits no residue, leaves the gun clean and clear, and the utmost it does is to leave a gentle dew of clear water on the inside of the bore, this water being the condensed steam which forms one of the products of its decomposition. Gun-cotton is, therefore, superior to gunpowder in not fouling the gun, a result favourable both to quicker and more accurate firing. It is further a matter of no slight convenience that gun-cotton makes no smoke. In mines the smoke of gunpowder makes the air unbreathable, and for some time after explosion the miners cannot return to their work. In boring the great tunnel of Mont Cenis through the Alps, the delay from smoke of powder alone will postpone the opening of the line for many months. After a properly-conducted explosion of gun-cotton, the workmen may proceed in their work at once without inconvenience. In casemates of fortresses, gunpowder fills the casemates with foul smoke, and the men speedily sink under the exertion of quick firing. By using gun-cotton it was ascertained that the men could continue their work unharmed for double the quantity of firing. This is partly attributed to the greater heat, and partly to the foulness of the air produced by gunpowder. But it is under the decks of our men-of-war, that greatest benefit is likely to arise from gun-cotton. Not only does the smoke of a broadside fill the between decks with hot and foul air, but the smoke of the windward gun blinds the sight, and hinders the aim of the leeward. When there is no smoke, as with gun-cotton, the aim of every gun may be precise and deliberate. The diminished heat between decks will also tell powerfully in favour of gun-cotton. In our armour-plated ships also there is more value in breech-loading guns, than in any other use of artillery. It is one of the necessities of breech-loading mechanism, that it be kept clean, and nothing tends more to derange its perfect action than the greater heat which gunpowder imparts to the gun from which it is fired. That gun-cotton has the convenience of not heating the gun has been thus proved. 100 rounds were fired in 34 minutes with guncotton, and the temperature of the gun was raised 90°. 100 rounds were fired with gunpowder, and triple the time allowed to cool the gun, which nevertheless was heated so much as to evaporate water with a hissing sound, which indicated that its temperature was much above 212°. Under these circumstances the firing with gunpowder had to be stopped, while that with gun-cotton was comfortably continued to 180 rounds. It is also a matter of practical convenience that gun-cotton, insomuch as it is lighter, can be carried more easily and farther than gunpowder; and it may be wetted without danger, so that when dried again in the open air, it is as good for use as before. III. We have now to ask-is it cheaper? The answer to this question must be qualified-pound for pound it is dearer; we must |