and its Application to the Aqueous Vapour of the Atmosphere. 355 



while the vapour passing into the space abCD with the force 

 f(t) —f{t') must be immediately condensed. Thence it imme- 

 diately follows that, if the temperature t ! of the upper space 

 continues constant while the temperature of the lower space 

 gradually increases, the pressure upon the upper surface C D 

 is increased, according to Dalton's theory, only by the expan- 

 sion of the air, but not by the newly-forming vapour itself, 

 whereas, according to my hypothesis, besides the effect which is 

 produced by the expansion of the air, a very considerable aug- 

 mentation of the pressure arises from the newly-formed vapour. 

 As the conditions here indicated admit of being practically 

 placed in operation, we have a simple and certain means of 

 coming to a decision regarding the correctness of Dalton's 

 theory ; and the only thing requisite is to arrange an appropriate 

 contrivance for the experiment. I have selected the following : 

 A glass tube bent in the form represented in fig. 2 was provided 

 at one end with a globe K, whilst the other end e was left open ; 

 in the straight part de, it was made to contain a drop of quick- 

 silver, q. The curved part ckd of the tube was plunged into a 

 vessel, B B, filled with cold water ; into the vessel A A, where the 



c a 



Fig. 2. 



q; 



B 





B 



X 



i 

 i 

 i 



Kit 



"N 



globe K was placed, cold and warm water could in turn be poured. 

 The globe K was first filled with dry air; and the experiment 

 showed that if the temperature was increased from 15°* 7 to 

 41°*8, the drop of quicksilver moved forwards by 11*47 Paris 

 inches. 



During this experiment, a thermometer placed in the vessel 

 B B stood at 12°. Afterwards the globe was opened by break- 

 ing off the fine point «, some water introduced, and the point 

 again joined on by melting. Again cold and warm water 

 were poured into the vessel A A whilst the temperature of the 

 tube remained unaltered, by which means, according to the 

 theory of Dalton, a rise of temperature from 15°*7 to 41°*8 

 would, if the vapour had not penetrated in the tube up to the 

 drop of quicksilver, move the latter as before 11*47 inches, and 

 if the vapour had so penetrated, at the most -^ih further ; instead 



