250 



H. Wild on the Absorption of 



right, were put, by means of fork- shaped caoutchouc tubes, in 

 communication with one and the same caoutchouc tube, and 

 the two most distant tubes were similarly connected with another 

 caoutchouc tube. In this manner the same kind of air could 

 be introduced on both sides into tubes of different lengths. The 

 current of air was now furnished by a larger pair of bellows 

 filled with air and pressed by weights; and in order to dry this 

 air or to saturate it with aqueous vapour, four U-shaped tubes 

 were employed, containing either concentrated sulphuric acid or 

 distilled water. 



A preliminary experiment was made by conducting alternately 

 dry and moist air only into the two most distant tubes on oppo- 

 site sides, so that each time on the right the stratum of air ex- 

 perimented upon was 45 centims. thicker than on the other side. 

 For the sake of comparison, the tubes were lastly filled with coal- 

 gas. The observations with telescope and a scale gave the fol- 

 lowing positions of equilibrium of the magnet- mirror : — 



Gas in the outer 

 tubes. 



Scale-reading. 



Difference. 



Dry air 



millims. 

 390 

 405 

 385 

 395 

 375 

 352 

 490 



millims. 

 18 

 15 

 15 



138 



Moist air 



D rv air 





Dry air 



Air in room 



Coal-gas 





The differences are formed by comparing the mean of two 

 readings for dry air, with the intermediate reading for moist air. 

 The temperature of the air was 20° C. Now, since by heating 

 the right-hand side of the thermopile (where the thicker gas- 

 stratum was interposed) a deflection towards the smaller numbers 

 of the scale ensued, these experiments also establish the greater 

 absorption by moist air. 



In order to increase the action, and in all cases constantly to 

 maintain on both sides a current of the same kind of air towards 

 the thermopile on the one hand, and the sources of heat on the 

 other, dry air was conducted in a subsequent experiment into the 

 outer tubes and moist air into the two inner ones, and these con- 

 ditions were again reversed. In this manner the following results 

 were obtained : — 



