5:2 1 Prof. TyndalPs Contributions to Molecular Physics. 



period, the sulphuric ether is the more powerful absorber. For 

 the radiation from hot carbonic acid, the absorption of sulphuric 

 ether, as shown in Table XXXV., is between 6 and 7 per cent. 

 in excess of that of formic ether ; while for the radiation from 

 hot aqueous vapour, the absorption by formic ether, as shown in 

 Table XXXVI., is 7 per cent, in excess of that by sulphuric. 

 That the periods of aqueous vapour, as compared with those of 

 carbonic acid, are slow, may therefore be inferred from these 

 experiments. 



The two following Tables illustrate the action of carbonic acid 

 gas and olefiant gas respectively, on the radiation from a flame 

 of hydrogen : — 



Table XXXVII. — Radiation through Carbonic Acid Gas. 

 Source, hydrogen-flame. 



Tension hi inches. Deflection. Absorption. 



1 5-5 7-4 



2 9-5 12-8 

 4 11-0 14-9 



30 190 25-7 



Total heat . 48-5 100-0 



Table XXXVIII. — Radiation through Olefiant Gas. Source, 



hydrogen-flame. 

 Tension in inches. Deflection. Absorption. From Table XXXVII. 



1 12-0 16-2 7-4 



2 18-0 24-3 12-8 

 4 24-0 32*4 14-9 



30 385 58-8 25-7 



Total heat . 48-5 100-0 100-0 



A comparison of the last two columns, one of which is trans- 

 ferred from Table XXXVII., proves the absorption of the rays 

 from a hydrogen-flame by olefiant gas to be about twice that of 

 carbonic acid ; while, when the source was a carbonic-oxide flame, 

 the absorption by carbonic acid at small tensions was more than 

 twice that effected by olefiant gas. 



§ XI. Radiation through liquids. — Influence of period. — Conver- 

 sion of long periods into short ones. 



Water at moderate thickness is a very transparent sub- 

 stance; that is to say, the periods of its molecules are in 

 discord with those of the visible spectrum. It is also highly 

 transparent to the extra-violet rays ; so that we may safely infer 



