chambers become more unequal in length, and that the sum of the absorptions of the two chambers is a maximum, when the medial rocksalt plate divides the long tube into two equal compartments. In these days a special interest attaches itself to the radiation of any gas through itself or through any other gas having the same period of vibration. The speaker referred to the results of an elaborate series of experiments on this interesting question. The experimental tube, 49.4 inches long, was divided into two compartments by a parti tion of rock-salt. All external sources of heat were abolished, and the pile, furnished with its conical reflector, stood at the end of the tube. The compartment nearest the pile contained the gas which was to act as absorber, while that most distant from the pile held the gas which was to act as radiator. It is known that the destruction of the motion of a sensible mass of matter is always accompanied by the evolution of heat. A weight falling to the earth, and a ball striking a target, are heated on collision. The same is true for atoms, and in the present experiments the gas in the radiating chamber was heated by the collision of its own particles against the inner surface of the tube when they rushed in to fill the vacuum. The radiation was, in fact, what the speaker had named “ dynamic radiation." The lengths of the two chambers were varied, the radiating column being lengthened and the absorbing one shortened at one and the same time; the sum of both was always the constant length 49.4 inches. The experiments with the vapours were thus executed. Both the chambers into which the tube was divided were, in the first place, occupied by the vapour to be examined; the usual pressure being 1-60th of an atmosphere. The entrance of the vapour was so slow, and its quantity so small, that the radiation due to the warming of the vapour by its own collision was insensible. The needle being at zero, dry air was allowed to enter the chamber most distant from the pile. This air became heated dynamically, communicated its heat to the vapour, and the latter immediately discharged the heat thus communicated to it against the pile. It is quite evident, that not only does this case resemble, but that it is actually of the same mechanical character as that in which a vibrating tuning-fork is brought into contact with a surface of some extent. The fork, which before was inaudible, becomes at once a copious source of sound. What the sounding-board is to the fork, the compound molecule is to the elementary atom. The tuning-fork vibrating alone is in the condition of the atom radiating alone, the sound of the one and the heat of the other being alike insensible. But in association with sulphuric or acetic ether-vapour the elementary atom is in the condition of the tuning-fork applied to its sound-board, communicating through the molecule motion to the luminiferous ether, as the fork through the board communicates its motion to the air. The experiments demonstrate the great opacity of a gas to radiations from the same gas. They also show in a very striking manner the influence of attenuation in the case of vapour. The individual molecules of a vapour may be powerful absorbers and radiators, but in thin strata they constitute an open sieve through which a large quantity of radiant heat may pass. In such thin strata, therefore, the vapours, as used in our experiments, were generally found far less energetic than the gases, while in thick strata the same vapours showed an energy greatly superior to the same gases. The gases, it will be remembered, were always employed at a pressure of one atmosphere. A few striking experiments were referred to in illustration of the influence of a paper lining, or a coat of varnish or lampblack, within the experimental tube. In dynamic radiation it is not possible to do entirely away with the action of the interior surface of the tube itself. When the tube is of brass and well polished within, the entrance of the air produces a deflection of 7.5 degrees, this being due to the emission from the warmed surface of the tube. A lining of paper two feet long raises the radiation sufficiently to drive the needle through an arc of 80 degrees, while a ring of paper 14 inches long placed within the tube radiates sufficient to urge the needle through an arc of 56 degrees. The speaker finally examined the diathermancy of the liquids from which his vapours were derived, and the result leaves no shadow of a doubt upon the mind, that both absorption and radiation are molecular phenomena, irrespective of the state of aggregation. If any vapour is a strong absorber and radiator, the liquid whence it comes is also a strong absorber and radiator. The molecule carries its power, or want of power, through all its states of aggregation. The order of absorption in liquids and vapours is precisely the same; and the speaker looked forward with hope to the application of these results to other portions of the domain of thermotics. [J. T.] EXTRA EVENING MEETING, Tuesday, June 23, 1863. H.R.H. THE PRINCE OF WALES, Vice-Patron, in the Chair. CAPT. SPEKE, On the Discovery of the Source of the Nile. [No Abstract received.] GENERAL MONTHLY MEETING, Monday, July 6, 1863. WILLIAM POLE, Esq. M.A. F.R.S. Treasurer and Vice-President, in the Chair. General Theophilus Boileau, F.R.S. were elected Members of the Royal Institution. The Secretary read the following communication from H.R.H. The Prince LOUIS OF HESSE: "Jagdschloss, Kranichstein, near Darmstadt, June 19, 1863. "SIR, I have been commanded by His Royal Highness The Prince Louis of Hesse to acknowledge the receipt of your letter, in which you inform His Royal Highness of the election as an Honorary Member of the Royal Institution. "His Royal Highness has been very much flattered by this election, and hopes in accepting it, that during a future stay in England, His Royal Highness will find more opportunities to attend the lectures of the Royal Institution. "I have the honour to be, Sir, "DR. H. BENCE JONES, Honorary Secretary, R.I." The Secretary announced, That a Member of the Royal Institution (who wished his name to be withheld) had presented the sum of Twenty Pounds, to be added to the Holland Fund. He also announced, that the Annual Donations of Sir HENRY HOLLAND, of Sir RODERICK I. MURCHISON, and of Mr. S. R. SOLLY, for the purchase of Scientific Apparatus, would in future, with their consent, be incorporated in one fund, to be entitled, "The Donation Fund for the Promotion of Experimental Researches." The Special Thanks of the Members were returned to E. SONSTADT, Esq. for his valuable present, through Professor FARADAY, of three specimens of the metal Magnesium, in three different stages of manufacture, weighing respectively 2039, 139, and 41 grains. The PRESENTS received since the last Meeting were laid on the table, and the thanks of the Members returned for the same: viz.— FROM American Journal of Natural Sciences-Proceedings, Nos. 1, 2. 8vo. 1863. Astronomical Society, Royal-Monthly Notices, No. 7. 8vo. 1863. Bavarian Academy, Royal-Sitzungsberichte, 1862. Band II. Heft 3 & 4. 1863. Band I. Heft 1 & 2. 8vo. Beke, C. T. Ph. D. (the Author)-Who discovered the Sources of the Nile? (K 90) 8vo. 1863. Belgique, Academie Royale de-Bulletins des Sciences. 1862. 8vo. 1863. Catholic University of Ireland-The Atlantis. Nos. 7, 8. 8vo. 1863. Technologist for June, 1863. Practical Mechanics' Journal for June, 1863. 4to. 8vo. Franklin Institute of Pennsylvania-Journal, No. 449. 8vo. 1863. 8vo. Garner, Robert, Esq. (the Author)-Figures illustrating the Structure of various Geological Institute, Vienna-Jahrbuch, Band XIII. No. 1. 4to. 1863. 8vo. Macilwain, George, Esq. M.R.I. (the Author)-Remarks on Ovariotomy. (A Postscript to his Work on Tumours.) 8vo. 1863. Manning, Frederick, Esq. M.R.I.-Engraving of Dr. Donne's Monument in St. Paul's. [Inserted in Walton's Lives.] Newton, Messrs.-London Journal (New Series) for June, 1863. 8vo. Oliveira, Benjamin, Esq. F.R.S. M.R.I. (the Author)-On the Works of the Isthmus of Suez Canal, in April, 1863. (K 90) 8vo. 1863. Petermann, A. Esq. (the Editor)—Mittheilungen aus dem Gesammtgebiete der Geographie. 1863. No. 5. 4to. Photographic Society-Journal, No. 134. 8vo. 1863. Royal Society of London-Proceedings, No. 53. 8vo. 1863. Sillimans, Professors (the Editors)—American Journal of Science and Arts, No. 105. May, 1863. 8vo. Stanford, Mr. E. (the Publisher)—Map of the Route explored by Captains Speke and Grant, from Zanzibar to Egypt, showing the Outfall of the Nile from the Victoria Nyanza Lake: Feb. 26, 1863. Statistical Society-Journal, Vol. XXVI. Part 2. 8vo. 1863. Taylor, the Rev. William, F.R.S. M.R.I.—A True Account and Declaration of the Horrid Conspiracy against the late King, &c. fol. 1685. United Service Institution, Royal-Journal, No. 25, and Appendix. 8vo. 1863. Vereins zur Beförderung des Gewerbsfleisses in Preussen-Verhandlungen, Jan. Feb. 1863. 4to. Yates, James, Esq. F.R.S. M.R.I.-The Metric System: its Prospects in this country, by the Rev. John Kerr. (K 89) 8vo. 1863. Royal Institution of Great Britain. 1863. GENERAL MONTHLY MEETING. Monday, November 2, 1863. The Rev. J. BARLOW, M.A. F.R.S. Vice-President, in the Chair. Captain Douglas Galton, R.A. F.R.S. Leonard Jaques, Esq. William Noble, Esq. The Hon. Josceline W. Percy. Allan Roskell, Esq. William Sterry, Esq. were elected Members of the Royal Institution. George Henry Strutt, Esq. was admitted a Member of the Royal Institution. The Secretary announced the following additions to "the Donation Fund for the Promotion of Experimental Researches" (see page 151). Sir John P. Boileau, Bart. £20 The Rev. John Barlow 20 10 The Special Thanks of the Members were returned to ISAAC LOWTHIAN BELL and Brothers, of Newcastle-upon-Tyne, for their valuable gift of Seven Pounds of Sodium. The PRESENTS received since the last Meeting were laid on the table, and the thanks of the Members returned for the same: viz.— FROM The Trustees of the British Museum—Himyaritic Inscriptions from Southern Arabia. Folio. 1863. Phoenician Inscriptions from Carthage. Folio. 1863. Governor-General of India-Memoirs of Geological Survey of India : Palæontologica Indica. No. II. 4, 5. 4to. 1863. French Government-Documents Inédits de l'Histoire de France :- Cartulaire de l'Abbaye de Redon en Bretagne. Ed. A. De Courson. 4to. 1863. Négotiations, Lettres et Pièces relatives à la Conférence de Loudun, 1616. Ed. M. Bouchitté. 4to. 1862. Vol. IV. (No. 39.) M |