256 Dr. Schuster on 



Society of London a paper {Proc. Roy. Soc, X., p. 385) in 

 which a number of experiments on radiant light were 

 described. It was mentioned that the amount of light 

 radiated by coloured glasses is in proportion to their depth 

 of colour, transparent glass giving out very little light; also 

 that the radiation from red glass has a greenish tint, while 

 that from green glass has a reddish tint. It was also shown 

 that when black and white porcelain is heated in the fire, 

 the black parts give out much more light than the white, 

 thereby producing a curious reversal of the pattern. 



In another paper {Proc. Roy. Soc. X.) an experiment was 

 described showing that tourmaline, which absorbs the ordi- 

 nary ray so that the transmitted light is polarised, radiates 

 the same ray in excess when hot, but that when the heated 

 tourmaline is viewed against an illuminated background of 

 the same temperature as itself, this peculiarity disappears. 



The Proceedings of the Roy. Soc. (XL, p. 193) contain 

 a short theoretical note on the internal radiation in uniaxial 

 crystals, in which the different refractive indices in different 

 directions are considered. 



Another important problem connected with the theory 

 of radiation occupied Stewart's mind, and led to a joint 

 experimental investigation with Professor P. G. Tait. When 

 all bodies in an enclosure through which no heat is allowed 

 to pass are at rest, we know that equilibrium of temperature 

 establishes itself But this is no longer necessarily true 

 when one of the bodies is in motion. A body whose par- 

 ticles are vibrating in the same period will, when in rapid 

 motion, appear to send out rays of different refrangibilities, 

 according as it is viewed from the front or from behind. 

 Similarly its absorptive properties will be altered. It is 

 not quite easy to see what relations must hold between 

 absorption and radiation, in order that a body may retain 

 the same temperature whether at rest or in motion. Stewart 

 and Tait tried to solve the problem by experiment, and 



