378 Prof. Magnus on the Constitution of the Sun, 



Whether the soda exists in the luminous flame in the form of 

 vapour, or whether single torn off pieces of this body increase 

 the illuminating power, will not here be considered ; for the sake 

 of brevity I will choose the designation soda- vapour. When, 

 instead of this vapour, a piece of platinum was brought into the 

 part of the flame which was experimented upon, a still greater 

 radiation of heat occurred. Obviously the platinum plate abs- 

 tracted more heat than the soda, and yet the radiation was 

 greater. By taking a plate 55 millims. in diameter, the radia- 

 tion from the flame amounted to nearly double as much as pre- 

 viously, when the flame was non-luminous. Whether a platinum 

 plate somewhat thicker or thinner was used made no apparent 

 difference, provided that it had always the same diameter. But 

 if, instead of making the plate thicker, it was covered with car- 

 bonate of soda, then the radiation would increase afresh, and so 

 considerably as to become half as much greater as before, when 

 the plate without sodium was used. 



The radiation rose still higher when, in addition to platinum 

 covered with soda, there was also present sod a- vapour in the 

 flame, arising from soda on a platinum wire placed deep in the 

 flame where the soda could not directly radiate against the pile, 

 as was above described. 



In the flame altogether saturated with soda- vapour, the plati- 

 num covered with soda radiated nearly three times as much heat 

 as the non-luminous flame. 



Lithium and strontium-salts acted like sodium-salts. 



These experiments show that gaseous bodies radiate very much 

 less heat than solids or liquids ; it can therefore hardly be main- 

 tained that a gaseous or vaporous {dampfformige) photosphere is 

 the seat of the solar heat. They show, further (and it is very 

 remarkable), that ignited soda has much more radiating power 

 than platinum heated to an equal temperature. 



Furthermore, they show that the soda-vapour or the fine par- 

 ticles of soda absorb only a little of the heat which is evolved by 

 the solid or liquid body ; for the radiation of the solid body in 

 the flame charged with soda- vapour was indeed always less than 

 the sum of the radiation of the solid body alone and the vapour 

 alone, but it was only a little less than this sum. 



This behaviour of ignited soda in the liquid and gaseous form 

 supports KirchhofFs theory of the constitution of the sun in 

 a striking manner. 



