218 GENEVA SOCIETY OF PHYSICS AND NATUEAL HISTORY. 



the course of the rays is different from that which had been indicated 

 by Bravais. 



MM. Soret and Sarasiu have made a summary of their work, inserted 

 in the Archives de la Bibliotheque Universelle, No. 215, p. 253, on the 

 rotatory power of quartz. The employment of the spectroscope, with 

 the fluorescent eyeglass devised by M. Soret, admits of the extension 

 of these limits to the ultra-violet part of the spectrum as far as the 

 line N ; and by the interposition of a plate of cobalt-blue glass, which 

 arrests tbe mean red and orange rays, they succeeded in clearly dis- 

 tingaishing the lines a and A, by which they were then able to measure 

 the rotatory power of quartz. These researches complete, as regards 

 the extreme red and ultra-violet, the results obtained by Bloch and 

 Stefan. 



Mr. N. Lockyer, of London, an honorary member of our society, did 

 us the honor of presenting the principal results of his researches 

 in spectral analysis. This scientist mentioned the different spectral 

 methods, the distinction which he established between the short and 

 long lines of the spectra, the different conditions in which the vapors of 

 bodies may be found, the modilications that the atomic grouping of those 

 bodies may undergo, and the effects in the spectrum by which these 

 modifications manifest themselves. 



M. Eaoul Pictet placed before us a communication on the application 

 of the mechanical theory of heat to the study of volatile liquids, and 

 the simple relations existing between latent heat, atomic weights, and 

 the tension of vapors. There results from this work, which was inserted 

 in the Archives de la Bibliotheque Universelle, No. 217, p. 66, 1st, that all 

 liquids have the same cohesion ; 2d, that the derivative of the Naperian 

 logarithm of the quotient of the tensions in relation to the temperatures 

 is constant for all liquids at the same pressure and temperature; 3d, 

 that the latent heat of all liquids under the same pressure multiplied by 

 their atomic weights at the same temperature gives a constant product; 

 4th, that for all liquids the difference of the internal latent heat at any 

 two temperatures whatsoever multiplied by the atomic weight is a con 

 staut number; 5th, that the latent heats of all liquids are multiples ot 

 their specific heats. 



Professor TVartmanu presented to the society various models of 

 Crooke's radiometer, manufactured at Bonn by M. Geissler. The radia- 

 tions from a luminous source act upon the wheel, and repel the blackened 

 faces. Nevertheless, by covering the latter, M. Wartmann showed that 

 the rays from the sun, or from sources of high temperature, repel also 

 the white faces. The interposition of colored glasses diminishes more 

 or less the rapidity of the motion, which continues very rapid in the 

 focus of a lens of sulphuret of carbon saturated with iodine. By acting 

 upon one paddle only, M. Wartmann found that it remained in a state of 

 equilibrium when the intensity of the radiation concentrated on the 

 black face and the opposite white face is in inverse ratio to the absorb- 



