Prof. TyndalPs Contributions to Molecular Physics. 51 1 



Table XV. — Absorption of heat by Vapours. Tension 0*5 

 of an inch. 







Source, platinum spiral. 



A 





Name of vapour. 



Barely 

 visible . 



Bright 

 red. 



White 

 hot. 



Near 

 fusion. 



Bisulphide of carbon 



. 6-5 



4-7 



2-9 



25 



Chloroform . . . 



. 9-1 



6-3 



5-6 



3*9 



Iodide of methyle . 



. 12-5 



9-6 



7-8 





Iodide of ethyle . . 



. 21-0 



17-7 



12-8 





Benzole .... 



. 26-3 



20-6 



16-5 





Amylene .... 



. 35-8 



27-5 



22-7 





Sulphuric ether . 



. 43-4 



31-4 



25-9 



23-7 



Formic ether 



. 45-2 



31-9 



25-1 



21-3 



Acetic ether . . . 



. 49-6 



34-6 



27-2 





The gradual augmentation of penetrative' power as the tem- 

 perature is augmented is here very manifest. By raising the 

 spiral from a barely visible heat to an intense white heat, we 

 reduce the absorption, in the cases of bisulphide of carbon and 

 chloroform, to less than one-half. At barely visible redness, 

 moreover, 56*6 and 54*8 per 100 get through sulphuric and 

 formic ether respectively ; while, of the intensely white-hot spiral, 

 76'3 and 78'7 per 100 pass through the same vapours. By 

 augmenting the temperature of solid platinum, we introduce into 

 the radiation waves of shorter period, which, being in discord 

 with the periods of the vapours, get more easily through them. 



What becomes of the more slowly recurrent vibrations as the 

 more rapid ones are introduced ? Do the latter take the place of 

 the former ? This question is answered by experiments made 

 with an opake solution of iodine, and with lampblack. As the 

 temperature of the platinum spiral increases from a dark heat to 

 the most intense white heat, the absolute quantity transmitted 

 through both these bodies steadily augments. But this heat is 

 wholly obscure, for both the solution and the lampblack intercept 

 all the luminous heat. Hence the conclusion that the augmen- 

 tation of temperature which introduces the shorter waves aug- 

 ments at the same time the amplitude of the longer ones, and 

 hence also the inference that a body like the sun must of neces- 

 sity include in its radiation waves of the same period as those 

 emitted by obscure bodies. 



§ VIII. Changes of the position of diathermic bodies through 

 changes of temperature of the same source. — Radiation from 

 lampblack compared with that from platinum at the same tem- 

 perature. 



Running the eye along the numbers which express the absorp- 

 tions of sulphuric and formic ether in Table XV., we find that, for 



