208 GENEVA SOCIETY OF PHYSICS AND NATURAL HISTORY. 



negatively. Professor Thury intends resuming and continuing these 

 experiments. 



M. Soret read before the society a memoir, inserted in No. 199 of the 

 Archives, under date of July, 1874, on polarization by diffusion of light. 

 He described and discussed in his memoir the experiments that he made 

 on the reflecting power of flames on the proper colors of bodies, and on 

 the cause of the illumination of transparent bodies and the diffusion of 

 light; experiments in which he studied a large number of crystalline 

 substances, such as quartz, diamond, rock-salt, etc. 



M. Soret also presented a memoir on the phenomena of diffraction 

 produced by a circular grating, a paper inserted in April, 1875, in No. 

 208 of the Archives. He gives the name of circular grating to opaque 

 screens pierced by a series of circular openings presenting the form of con- 

 centric rings. He further indicates the method he took for constructing 

 such a grating, and for producing upon a glass plate of small dimensions 

 a series of 19G concentric rings, alternately transparent and opaque, the 

 central part being transparent in the positive grating and opaque in 

 the negative grating; and the radii of the circles bounding these 

 rings increasing proportionally to the square roots of the series of nat- 

 ural numbers. He has shown that a circular grating of this kind can 

 perform the office of a non-achromatic object-glass; an inverted image 

 is produced of a distant luminous object, and this image passes through 

 the different colors of the spectrum, according to the distance of the 

 grating. 



M. K. Pictet communicated the results of his experiments made in 

 Egypt on the propagation of the calorific rays of the sun through differ- 

 ent substances, sand among others. He undertook to verify the idea ex- 

 pressed by M. Soret, that sand acts after the manner of a plate of glass ; 

 that is to say, it would be found diathermanous to luminous heat and 

 athermanous to dark heat. M. Pictet found, in fact, in the action of 

 temperature, more agreement of sand with glass than with other sub- 

 stances, such as wood or sheet-iron, even when the latter were painted 

 the color of sand. 



The same member explained to the society a new process for the manu- 

 facture, on a large scale, of sulphurous acid, which consists in pouring 

 sulphuric acid, drop by drop, on sulphur, heated to from 300° to 350c> 

 C. (572° — 6620 F.), in a cast-iron retort. He stated some of the proper- 

 ties of the sulphurous acid prepared in this way, as well as those of the 

 sulphite of water, obtained by the addition of water in a determined 

 proportion. 



M. E. Demole read a work, inserted in No. 204 of the Archives, De- 

 cember, 1874, on the question of molecular transpositions in the aromatic 

 series. Taking up again the experiments of M. Lautemann on the prod- 

 ucts of the distillation of oxysalicylic acid, M. Demole reached the con- 

 clusion that the products obtained by the latter were due to the circum- 

 stance that the oxysalicylic acid employed was not pure, but contained 



