November 29, 1900] 



NA TURE 



123 



which the gas first passes, to an outlet whence it can return to 

 the main supply pipe. The liquid which separates from the gas 

 is ultimately collected in a vacuum vessel. The apparatus, with 

 the exception of the compressor, motor and Hampson air 

 liquefier, is comparatively inexpensive. About 50/. is required 

 for the additional apparatus, and each time liquid hydrogen is 

 made involves a further expenditure of about a sovereign. Dr. 

 Hampson said he would like to offer a correction. Dr. Travers 

 had said that he (Dr. Hampson) was the first to liquefy air by 

 the application of the counter current process to the Joule- 

 Thomson effect. Although he was the first to make the pro- 

 posal he was not the first to apply it. He made the proposal 

 to Prof. De war's assistant in 1894, and air was liquefied by Prof. 

 Dewar by this method. Dr. Travers had referred at length to a 

 valve which he (Dr. Hampson) had devised, but as it was straight- 

 forward common sense he did not wish to accept any credit for 

 the use it had been to the author in his experiments. 

 He would like to call attention to the remarkable features of 

 the work in two respects — the economy of means and the 

 magnitude of results. By means of liquid hydrogen Prof. 

 Ramsay and Dr. Travers had succeeded in obtaining the 

 physical and other properties of some of the rarer gases. Prof. 

 S. P. Thompson said the author had asserted that the Joule- 

 Thomson effect for hydrogen changes in sign at some tempera- 

 ture, and expressed his interest in the fact that it was possible 

 to get a cooling effect by allowing hydrogen to expand. Mr. 

 B )ys asked if it was necessary or desirable to allow the hydrogen 

 to expand to atmospheric pressure. Dr. Travers said the 

 mechanical advantages of this were great. Dr. Lehfeldt asked 

 if there had been any attempt to determine the temperature of 

 the liquid, and, secondly, if the apparatus could be employed to 

 determine the magnitude of the Joule-Thomson effect. Dr. 

 Harker asked if the temperature at which the Joule-Thomson 

 effect changes sign was known. Dr. Donnan said that the 

 efif'Ct changed sia;n at the temperature at which " PV " was 

 a minimum. Dr. Travers, in reply to Dr. Lehfeldt, 

 said he had not determined the temperature of the 

 liquid, and the apparatus was not suitable for measur- 

 ing the Joule-Thomson effect. He should say that the 

 change of sign occurred about —150° C. It was Daniel 

 Birthelot who first pointed out that the change of sign corre- 

 sponded with the minimum value of " PV," but the experi- 

 ments of Amagat oh the relation between pressure and volume 

 were not sufficienily accurate to fix the temperature. — A paper 

 on the anomalous dispersion of carbon, by Prof. R. W. Wood, 

 was taken as read. Experiments were made with smoke films 

 and with films deposited on plate glass in a vacuum by an in- 

 candescent lamp. The dispersion was first measured with a 

 Michelson interferometer, illuminated with monochromatic light 

 of various colours, obtained by prismatic analysis. The fringes 

 were photographed and measured, readings being obtained 

 between wave-lengths ■cxxx)40 cm, and '000066 cm. The 

 results show a steady increase of refractive index from blue to 

 red. The re(ractive index for sodium light was measured by 

 estimating the thickness of the film and the fringe displacement, 

 and was found to be 2*2. A prismatic deposit of smoke was 

 then made by allowing a piece of plate glass to move uniformly 

 backwards and forwards over the top of a small flame. 

 The deviation produced by this prism was measured by means of 

 a direct vision spectroscope with the prisms removed. Experi- 

 ments were performed with red and blue light. The mean 

 deviation of red and blue was taken for sodium light, and this 

 result was in good agreement with the deviation obtained by the 

 interferometer method. — A paper on the refraction of sound by 

 wind, by Dr. E. H. Barton, was taken as read. Assuming that 

 the wind is everywhere horizontal, and does not vary in any one 

 horizontal plane, but is different at different levels, then the 

 following results are obtained for rays in the same vertical plane 

 as the wind : (i) The direction of propagation is not usually at 

 right angles to the wave front where there is a wind, conse- 

 quently the cosecant law for the wave front needs supplementing 

 by another expression giving the direction of the ray. (2) Total 

 reflection cannot occur if the wave front is initially hori- 

 zontal. (3) In a region where the horizontal wind increases 

 uniformly as we ascend, the rays, instead of forming a catenary, 

 describe a more complicated curve, which, however, reduces to 

 a parabola in the special case of rays whose wave fronts are 

 horizontal. In the piaper the relation between direction of pro- 

 pagation and wave front is first worked out and then the refrac- 

 tion of waves and rays on crossing into a new wind zone is 



NO. 1622, VOX. 63I 



considered. This principle is then applied to the diffraction 

 through any number of parallel wind zones, and it is shown that 

 the final inclinations of wave fronts and rays are independent of 

 the characteristic constants of the intermediate zones. It is shown 

 that since a cosecant cannot have a value between -f i and - i, 

 total reflexion becomes possible. If, however, the wave front is 

 initially horizontal there is no refraction of the wave front and 

 no total reflexion, but the ray deviates without limit from the 

 vertical, and tends to correspond with the wave front. When 

 reflexion occurs it follows the ordinary optical law. The society 

 then adjourned until December 14, when the meeting will be 

 held at the Royal College of Science, South Kensington. 



Chemical Society, November 15. — Prof. Thorpe, President, 

 in the chair. — The following papers were read : — Trichlorobenz- 

 oic acid, by F. E. Matthews. Benzonitrile hexachloride is 

 acted upon by alcoholic soda with production of a mixture of 

 trichlorobenzoic acids from which a new trichlorobenzoic acid 

 was isolated ; the new acid gives an ester with hydrogen 

 chloride and alcohol and is, therefore, the i : 2 : 4-trichloro-3- 

 benzoic acid. — Oxidation of benzalthiosemicarbazone, by G. 

 Young and W. Eyre. Benzalthiosemicarbazone, 



CHPh:N.N:C(SH). NH2, 

 is oxidised to amidophenylthiodiazole, 



/.N . N.v 



CPh^ 



./ 



C . NH, 



by ferric chloride. Similar oxidation products are obtained 

 from the 4-substituted methyl and phenyl benzalthiosemicarb-, 

 azones. — The nitration of benzeneazosalicylic acid, by J. T. 

 Hewitt and J. J. Fox. With dilute nitric acid, benzeneazo- 

 salicylic acid yields benzeneazoorthonitrosalicylic acid, whilst 

 with strong nitric acid, paranitrobenzeneazosalicylic acid is ob- 

 tained. — Upon the collection and examination of the gases 

 produced by bacteria from certain media, by W. C. C. Pakes 

 and W. H. Jollyman. The strictly aerobic organism Bacilhis 

 pyocyaneus grows in media containing I per cent, of pota3siun> 

 or ammonium nitrate under anaerobic condition^ ; the authors 

 conclude that the terms aerobic and anaerobic must be extended 

 so as to include the presence of oxygen in the form of nitrates. 

 The gases produced by this organism from nitrated media con- 

 tain nitrogen and small quantities of oxygen. — The bases con- 

 tained in Scottish shale oil, by F. C. Garrett and J. A. Smythe. 

 The basic mixture separated from Broxburn shale oil seems to 

 contain no pyridine ; a-picoline, a7a'-trimethylpyridine, and 

 aj8- and oj3'-dimethyl pyridine were isolated from it. — On a 

 simplified method for the spectrographic analysis of minerals, by 

 W, N. Hartley and H. Ramage. 



Paris. 



Academy of Sciences, November 19. — M. Maurice Levy ir>> 

 the chair. — Note on the telescopic planets, by M. de Freycinet. 

 The asteroids studied, 428 in number, appear to belong to eight 

 independent rings, each of which, before breaking up into frag- 

 ments, turned as one piece round the sun. This hypothesis as- 

 to their formation requires three conditions, all of which are 

 shown to be fulfilled. — On the aerostatic observation of the 

 Leonids, by M. J. Janssen. The observations from the balloons 

 ascending from Paris were obscured by clouds, although an 

 altitude of over 13,000 feet was attained. Observations at other 

 stations were also spoiled by the state of the weather. — Sir Joseph 

 Hooker was elected a Foreign Associate in the place of the late 

 Prof. R. Bunsen. — Observations of the Leonid swarm at Meu- 

 don, by M. H. Deslandres. Only nine Leonids were seen on 

 the two nights. — On some applications of non-euclidian geo- 

 metry, by M. Servant. — On the summation of series, by M. 

 Emile Borel.— On a new shadow analyser, by M. J. Mace de 

 Lepinay. The new analyser may be used for any simple rays, 

 and preserves its sensibility in convergent light. By applying a 

 modification of Mouton's method, it is possible to measure easily 

 thicknesses up to several centimetres with an accuracy of 0"i4/x. 

 — On the electrocapillary properties of mixtures and electro- 

 capillary viscosity, by M. Gouy. — The direct combination of 

 nitrogen with the metals of the rare earths, by M. Camille 

 Matignon. A mixture of the oxide of the rare earth with alu- 

 minium and magnesium is heated in a tube containing air and 

 connected with a manometer. Under these conditions, with lan- 

 thanum, praseodidymium, neodidymium and samarium, the ab- 

 sorption of the oxygen and nitrogen is very rapid ; with cerium 



