Intelligence and Miscellaneous Articles. 211 



by bringing the radiating surface suddenly to 100° C. by a stream 

 of boiling water applied exteriorly. 



Of results must be mentioned, in the first place, that the absorp- 

 tion of radiant heat by aqueous vapour, in opposition to TyndalTs 

 results, is found to be excessively small. The authors show that 

 the contradiction between this result and certain meteorological 

 observations is only apparent. 



The experiments made by Yiolle on Mont Blanc show that one 

 metre of the air at the place of observation absorbed only 0*007 per 

 cent, of the total radiation. If account is taken of the hygrometric 

 condition of the air, and the dilference in wave-length of the heat 

 experimented upon, we arrive at the conclusion that, taking Yiolle's 

 observations as correct, it would require H layer of 300 metres 

 of saturated aqueous vapour at 12° to produce the absorption of 

 radiant heat which Tyndall finds for a length of 1*22 metre. By 

 this simple calculation, as well as by the experimental results ob- 

 tained, we may regard Magnus's view as established — that aqueous 

 vapour exerts hardly any absorption on radiant heat. 



The rest of the numbers obtained for gases agree fairly well with 

 those given by Tyndall (which of course is not the case with the 

 vapours examined). At atmospheric pressure the intensity of the 

 radiation through a column of 310 millims. length (the intensity of 

 the incident radiation being 100) is for 



Air 99-8 



Carbonic oxide 93*3 



Carbon dioxide 92*3 



Ethylene 51*8 



It appears, further, that there is no simple relation between 

 the absorption and the pressure of the substances experimented 

 upon ; and the absorption, even for the radiation from a source of 

 heat at 100°, is a selective one. Hence too much importance is 

 not to be attributed to the relation which is pointed out in the 

 present paper between absorption and chemical composition, which 

 is as follows. After the absorption for vapours at equal pressure 

 (that is, for an equal number of molecules) had been found by a 

 graphical method, it was seen that the absorption-coefficients for 

 radiation at 100° C. of the substances examined which belonged to 

 the fatty series might be arranged somewhat as follows : — 



I. Methyl- alcohol, formic acid, carbon monoxide, carbon dioxide, 

 chloroform. 

 II. Ethvl alcohol (acetic acid), ethyl ether, ethylene. 

 in. Butyl alcohol. 

 IV. Amyl alcohol. 



The absorption is nearly the same for the substances in each 

 series, but rises rapidly as the percentage of carbon increases. 



It seems to be otherwise with bodies belonging to other groups. 

 Thus, for example, benzol, notwithstanding its 6-carbon atom, pos- 

 sesses a somewhat small absorption- coefficient. "Whether this is a 

 consequence of the different linking of these carbon atoms and the 

 consequent modification of the mode of vibration, can onlv be de- 



