70 Royal Society : — Mr. 0. Reynolds on the Condensation 



the flask ; and if this is to remain constant, the pressure of air and 

 steam must be constant, and therefore, as the pressure of the air in- 

 creases, the pressure of the steam must decrease. This variation of 

 pressure is not very great ; and its effect may be allowed for on the 

 assumption that the condensation is proportional to the pressure of 

 steam. This is accomplished by dividing the drops by the pressure 

 of the steam. 



These methods, neither of which, as it appears, is rigorous, 

 seem nevertheless to be the best ; and fortunately the law which 

 the effect of the additions of air follows is of such a decided cha- 

 racter as to be easily distinguished; and the two methods give 

 results which are sufficiently concordant for practical purposes. 



10. The apparatus employed in these experiments consisted of a 

 glass flask, in which a surface-condenser was formed of a copper 

 pipe passing in and out through the cork. This pipe was kept 

 cool by a stream of water, and was so fixed that all the condensed 

 water dropped from it, and the drops could be counted. The flask 

 was freed from air by boiling ; the volume of air passed into the 

 flask could be accurately measured ; and ample time was allowed 

 for the air in the flask to produce its effect before more was admitted. 



For the experiments according to method I., the flame under the 

 flask and the stream of water through the condenser were kept con- 

 stant from first to last. For those made according to method II., 

 in one case the stream of water was kept constant, and in the other 

 it was altered, so that the efiluent water was kept at a constant 

 temperature. 



11. The results of these experiments are shown in Tables I., II., 

 III. 



The letters which head the columns have the following meanings : — 



/ stands for the volume of the flask in cubic centimetres. 



a stands for the volume of the air at the pressure of the atmo- 

 sphere. 



h stands for the height of the barometer in millimetres of mer- 

 cury at the time of the experiment. 



\ stands for the height of mercury in the gauge in millims. 



t stands for the temperature Centigrade of the effluent water. 



t x stands for the temperature of the water in the flask, found 

 from Begnault's tables of boiling-points. 



jp 1 =7fc — 7i x stands for the pressure within the flask in millims. of 



mercury. 



a t + 274 



p 2 = - -j- h — — eyf. stands for the pressure of the air within the 



flask corrected to the temperature T r 

 p 3 =Pj—jP 2 stands for the pressure of the steam. 



-*-2- stands for the ratio of the pressure of the air in the flask to 



that of the steam. 



