On the Correlation of two Planes. By T. A. Hirst. 8vo. 1894. On the Degenerate forms of Conics. By T. A. Hirst. 8vo. Solar Physics Committee Papers, 1879-80. By Professors Stokes, Lockyer and B. Stewart. Report on the Electric Light Experiments at Chatham in 1878. By Sir John Stokes. 8vo. Akustische Untersuchungen von W. Preyer. 8vo. 1879. Die Mathematischen Elemente der Erkenntnisstheorie von O. SchmitzDumont. 8vo. 1878. Memoir on Curves of the Third Order. By A. Cayley. 4to. 1856. La Relazione di Göpel per funzioni iperellittiche d'ordine qualunque. By F. Brioschi. 4to. 1881. Sopra un sistema di equazioni differenziali. By F. Brioschi. Sur la distinction des intégrales des équations différentielles linéaires en sous groupes. Par F. Casorati. 4to. 1881. Genneralizzazione di alcuni teoremi dei Sig. Hermite, Brioschi e MittagLeffler sulle equazioni differenziali lineari del 2° ordine. By F. Casorati. Aggiunte a recenti Lavori dei Sig. Weierstrass e Mittag-Leffler sulle funzioni di una variabile complessa. By F. Casorati. 4to. 1882. Sur un écrit très récent de M. Stickelberger. By F. Caso. 1881. Ein neuer Beweis für die Riemann'sche Thetaformel, vou F. Prijm. 4to. 1882. Sur quelques points de la théorie des Fonctions. Par C. Hermite. 4to. 1884. Sur un représentation analytique des fonctions au moyen des transcendantes elliptiques. Par C. Hermite. 4to. 1880. La Fonction Exponentielle. Par C. Hermite. 4to. 1874. Die Sechs Grade der Beweglichkeit eines unveränderlichen Systems, von W. Schell. On the Rolling of Sailing Ships. By W. H. White. 4to. 1881. On J. Amsler Laffon's Mechanical Integrator. By C. W. Merrifield. 4to. 1880. Richerche Microscopiche sulle tracce delle scintille elettriche incise sul vetro. Par E. Villari. 4to. 1883. Practical Results on the Preservation of Alimentary Substances. By F. Artimini. 8vo. 1885. Beobachtungen in Gauss' Erdmagnetischen Observatorium in Göttingen, von The Algebra of Relatives. By C. S. Peirce. 4to. 1882. Par R. Radau. Otto von Guerickes Experimenta Nova (ut vocantur) Magdeburgia. 4to. 1881. Note sur les méthodes de Wronski, &c. By A. J. Yvon Villarceau. 4to. 1881. Essai philosophique sur la Science de l'ordre. Par H. J. Yvon Villarceau. Also numerous Photographs, Drawings, &c. Surgeon-General's Office, U.S. Army-Index Catalogue of the Library, Vol. XV. 4to. 1894. Tacchini, Prof. P. Hon. Mem. R.I. (the Author)—Memorie della Società degli Spettroscopisti Italiani, Vol. XXIII. Disp. 9a. 4to. 1894. United Service Institution, Royal-Journal, No. 201. 8vo. 1894. United States Department of Agriculture-Monthly Weather Review for August, 1894. 4to. Experiment Station Record, Vol. V. Nos. 8-11. 8vo. 1894. Forestry Division Bulletin, Nos. 2, 4. 8vo. 1889-90. Farmers' Bulletin, Nos. 3-9, 13, 16, 17, 19. 8vo. 1891-4. United States Department of Agriculture-continued. Division of Statistics: Reports, Nos. 2, 5, 6. Svo. 1892-3. Division of Entomology: Bulletin, Vol. VI. Nos. 1, 3, 4. 8vo. 1893-4. Division of Chemistry: Bulletin, Nos. 25, 26, 37, 40. 8vo. 1890-4. United States Department of the Interior-Compendium of the Eleventh Census, Part 2. 4to. 1894. United States Geological Survey-Twelfth Annual Report, 1890-1, Parts 1, 2. 4to. 1891. Thirteenth Annual Report, 1891-2, Parts 1-3. 1892-3. United States Patent Office-Official Gazette, Vol. LXIX. Nos. 4-8. 8vo. 1894. Vereins zur Beförderung des Gewerbfleisses in Preussen-Verhandlungen, 1894: Heft 8. 4to. 1894. Winn, J. M. Esq. M.D. M.R.C.P. (the Author)—An Exposition of the Fallacies of the Materialistic Theory of Physiological Psychology. 8vo. 1894. WEEKLY EVENING MEETING, Friday, January 19, 1894. SIR FREDERICK BRAMWELL, BART. D.C.L. LL.D. F.R.S. PROFESSOR DEWAR, M.A. LL.D. F.R.S. M.R.I. Scientific Uses of Liquid Air. WHEN Faraday was working on liquid gases in this Institution about 1823, with such means as were then at his command, his inquiry was limited to the determination of the specific gravities and vapour pressures of such bodies. Twenty years later, by the use of solid carbonic acid, the greatest cold then possible was obtained, and Faraday made admirable use of Thilorier's new cooling agent to extend his early investigations. Just as liquid carbonic acid produced in glass tubes was of no use as an agent for effecting the liquefaction of more resisting gaseous matters, until it could be manipulated in the solid state, so liquid air, until it could be handled, stored and used in open vessels, like any ordinary liquid, could not be said to possess scientific uses in any wide sense. Such operations become easy when double-walled vacuum vessels (such as were described in a former lecture) are employed in the conduct of experiments where substances boiling at very low temperatures have to be manipulated. The chief scientific use of liquid air consists in the facilities it gives for the study of the properties of matter at temperatures approaching the zero of absolute temperature. In this lecture the expression liquid air may mean either oxygen or air. Where a constant temperature is required oxygen is used. Liquid air made on the large scale may contain, after it is collected in open vacuum vessels, as much as 50 per cent. of oxygen. Such a liquid boils between 192° and 182 C., and the longer it is stored the nearer it comes to - 182° C. or the boiling point of pure oxygen. For a number of experiments of a qualitative character, whether it is liquid air or oxygen that is used makes no difference. In many of the experiments to be recorded, liquid oxygen made from the evaporation of liquid air was employed. In pursuing this subject in consort with Professor Fleming,* a long series of experiments, involving the use of large supplies of liquid oxygen, have been carried out on the electric resistance of metals and alloys, and * The Electrical Resistance of Metals and Alloys at Temperatures Approaching the Absolute Zero.' By James Dewar, LL.D. F.R.S. and J. A. Fleming, M.A. D.Sc. F.R.S. Professor of Electrical Engineering in University College, London. Phil. Mag. 1892. the results warrant the conclusion that at the zero of absolute temperature all the pure metals would be perfect conductors of electricity. Under such conditions a current of electricity started in a pure metallic circuit would develop no heat, and therefore undergo no dissipation. Similarly, we infer there would be no Peltier effect at the zero. In other words, the passage of electricity from one metal to another would take place without evolution or absorption of heat. Further investigation, along with Professor Liveing, on the rcfractive index of liquid nitrogen and air, has led to the conclusion that the refractive indices of nitrogen and air are respectively for the D-ray, 1.2053 and 1·2062. In these determinations, instead of using the prisms we have employed the method of Terguem and Trannim, which consists in suspending in the liquid two plates of glass with a thin layer of air between them, and measuring the angle of incidence at which the chosen ray suffers total reflection at the surface of the air. As all the vacuum vessels are either spherical or cylindrical in form when filled with liquid, they act as lenses which are irregular and full of striations. Further, small bubbles of gas being given off in the liquid rendered any image indistinct when viewed with a telescope. In order to avoid the necessity of observing any image through the liquid, it was used simply as a lens to concentrate the light observed on the slit of a spectroscope. Under such conditions the observations were easily executed and the results satisfactory. For some time a series of observations on the thermal opacity of liquid oxygen and nitrogen have been projected. It is, however, exceedingly difficult to experiment in such a way as to eliminate the absorbing action of the glass vessels, and as the use of rock salt is impracticable, the absorption of heat of low refrangibility remains for the present undetermined. It is possible, however, to use the glass vacuum vessels to determine approximately the relative thermal transparency for heat of high refrangibility, such as is radiated by a colza lamp. The following results represent the heat transmitted through the same vacuum vessels filled with different liquids, taking chloroform as the unit for comparison and correcting for differences of refractive index. From this result it follows that liquid oxygen is nearly as transparent to high temperature heat radiation as chloroform, which is one of the most transparent liquids next to carbon bisulphide. Liquid ethylene is much more opaque. These results must, however, be considered only as an approximation to the truth, and as generally confirmatory of the inferences Tyndall drew as to the relation between gases and liquids as absorbents of radiant heat. On the Refractive Indices of Liquid Nitrogen and Air. By Professors Liveing and Dewar. Phil. Mag. 1893. Instead of silvering the interior and exterior of the vacuum vessels, it is found convenient when using mercury vacua to leave a little excess of liquid mercury, in order that the act of filling the inner vessel with liquid air should cause a fine silvery deposit of the metal over the exterior surface of the inner vessel. In such a vessel liquid air or oxygen shows no signs of ebullition, the surface remains as quiet and still as if it was ordinary water. The supply of heat is cut down to less than four per cent. of what it is without exhaustion and silvering in good vacuum vessels. The result is that volatile liquids can be kept thirty times longer. Such vessels do not, however, maintain indefinitely the high standard of heat isolation they possess the first time they are used. After repeated use all vacuum vessels employed in the storage and manipulation of liquid air deteriorate. Illustrations of the appearance of such vessels are given in Figs. 1 and 2. The rapidity with which a space is saturated with mercury vapour (which we know exerts a pressure of about one-millionth of an atmosphere) is easily proved by simply filling a barometer in the usual way, and then instantly applying a sponge of liquid air to a portion of the glass surface of the Torricellian vacuum space, when a mercury mirror immediately deposits. It is important to know the amount of mercury deposited from a saturated atmosphere which is maintained (containing excess of liquid mercury) at the ordinary temperature, the condensation taking place when liquid air or oxygen is discharged into a vessel surrounded by such a Torricellian vacuum. If the deposit on the cooled bulb is allowed to take place for a given time, the outer vessel can then be broken and the amount of mercury which coated the bulb ascertained by weighing. Knowing the surface of the cooled bulb, the amount deposited per unit of area can be calculated. In this way it was found that in ten minutes 2 milligrams of mercury per square centimetre of surface was deposited. Considering that one-tenth of a milligram of mercury in the form of saturated vapour at the ordinary temperature corresponds to the volume of 1 litre, this proves that the equivalent weight of 20 litres had been condensed in the space of ten minutes. This plan of cooling a portion of the surface of a vessel by the application of a liquid air sponge, enables us to test our conclusions as to the amount of matter present in certain vacua. Here is a globe of the capacity of 1 litre. It has been filled with, presumably, nothing but the vapour of mercury, by boiling under exhaustion and subsequent removal of all excess of liquid. Such a flask ought to contain mercury in the gaseous state that would weigh rather less than one-tenth of a milligram, assuming the ordinary gaseous laws extend to pressures of less than one-millionth of an atmosphere. Now we know by electric deposition that one-tenth of a milligram of gold can be made to cover one square centimetre of surface with a fine metallic deposit. Considering the general similarity in the properties of mercury and gold, we should therefore anticipate that if all the mercury vapour could be frozen out of the litre flask it would also form a mirror about one square centimetre in area. But after one such mirror is deposited, the renewed application of a second |