108 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



duced by a Bourbouze lamp with a refracting system of 

 flint-glass, (2) to study the variations of this spectrum with 

 the temperature of the source, and (3) to observe also the 

 absorption spectra of various bodies and their variations 

 with the temperature of the source. Among other impor- 

 tant facts observed, these experiments appear to prove finally 

 a variation in the distribution of heat in the spectrum with 

 the temperature, and also to show that flint-glass becomes 

 less diathermanous as the temperature falls. 



Aymonnet has also examined the specific absorbing power 

 of bodies for radiant heat, using a thermo-pile and prism, the 

 solution to be examined being placed between them. From 

 his results he concludes that the atomic absorbing power 

 appears to be constant, first, for all elementary bodies dis- 

 solved in the same menstruum, and, second, for all these bod- 

 ies when existing in compounds of analogous chemical con- 

 stitution. 



The same author has studied calorific spectra by a mod- 

 ification of the ordinary method. He concludes that heat 

 spectra contain easily recognized minima, that these minima 

 are periodic, that they change their position when the source 

 of heat is varied, that these variations are also produced by 

 absorption, and that by these absorption changes much light 

 is thrown upon the mechanism of solution. 



The radiometer continues to be the subject of extensive 

 experimentation. Among the papers which have appeared 

 upon it, one of the most noteworthy, perhaps, is that of Mr. 

 Crookes, in Nature, in which he says : " The results I have ob- 

 tained seem to show conclusively that the true explanation 

 of the action of the radiometer is given by Mr. Johnstone 

 Stoney, according to which the repulsion is due to the inter- 

 nal movements of the molecules of the residual gas." He 

 gives a number of highly interesting experiments with this 

 instrument. Alvergniat seems to have made an experimen- 

 tum cruris with the radiometer. By making the vanes of 

 aluminum and silver, and by maintaining the globe during 

 exhaustion at 400 C. in the vapor of sulphur, he obtained a 

 vacuum so perfect that there was no rotation. On admitting 

 a trace of air, however, rotation recommenced. Salet has 

 modified the instrument in a very simple way in order to 

 show the correctness of the molecular bombardment theory. 



