14 Prof. J. H. Jeans on the Interaction 



The following selenium compounds have been examined: — 



Table VI. 



Berzelianite. CruSe. Strikerum Mine, Sinalaud. 



White sublimate at 440°. 

 Eucairite, Cu 2 S, Ag 2 Se. Loc. as above. 



Tr. of red subl. at 380°. 



White subl. at 410°. 

 Clausthalite, PbSe. Tilkerode ; Harz. 



Tr. of red subl. at 340°. 



White subl. at 600°. 



Lead. 



The sublimate formed in air is PbO. It forms a yellowish 

 sublimate which shows bluush-white where it thins out on 

 the margins. The yellow colour intensifies upon heating. 

 Owing to its high specific gravity much of it falls into the 

 lower glass. Under the microscope it is finely granular. 

 It is soluble in solution of KHO and in HOI. 



The formation of this sublimate is at a higher temperature 

 than that at which the mineral breaks up. 3Iassicot, as an 

 olive-vellow slag, first forms Gradually on the hob as the 

 mineral decomposes. This melts at about 930 c . sublimation 

 beginning at a temperature approximating to 1000°. when it 

 progresses steadily. The sublimate is, therefore, obtained 

 below the temperature of volatilization of Bi 2 Q 3 and above 

 that of Te0 2 , but unless the temperature be carefully attended 

 to there is risk of lead oxide volatilizing along with the 

 latter sublimate. 



Iveao-h Geological Laboratorv. 



II. On the Interaction between Radiation and Free Electrons. 

 By J. H. Jeans, M.A., F.R.S* 



1. rriTIERE is now very general agreement that for a 

 J_ system of matter and aether to give Planck's formula 

 for the radiation in its final steady state, the motion of the 

 system mast be in some way different from that predicted 

 by the classical laws of dynamics as summarized in the 

 principle of Least Action. 



The problem of finding a new system of laws which shall 



lead to Planck's formula is as yet unsolved. In our present 



state of knowledge the problem is largely one of guessing. 



and the lucky guess has not yet been made. On the other 



* Communicated bv the Author. 



