356 Frof. Lamont on Dalton's Theory of Vapour, 



of which, the motion actually produced amounted to nearly the 

 double of this. It resulted from accurate measurement, that the 

 11 '47 inches were passed over as soon as the temperature had 

 been raised from 15°7 to 30°*9. 



A second glass tube was employed of a similar form, but with 

 a smaller globe; and with this, as long there was only dry air in 

 the globe, an increase of temperature of from 14 0, 4 to 44°'24 

 occasioned in the drop of quicksilver a motion of 12*86 Paris 

 inches ; but after a small quantity of water had been introduced 

 into the globe, the quicksilver moved the same distance when 

 the temperature was raised only from 14°*4 to 31°'l. As it 

 might be imagined that it was possible that, after a longer inter- 

 val of time, the vapour would extend up to the drop of quicksilver 

 and then produce a different, result, the globe was left for a 

 whole hour in warm water, but the position of the quicksilver 

 remained unchanged. 



Also, after the termination of the experiment, neither in the first 

 nor in the second tube could a trace be perceived of the vapour 

 having passed down into the bent part between c and d; so that 

 it probably penetrated into the tubes either not at all or only to 

 a small extent. On this supposition the observed effect would 

 require the conclusion that the increase in the expansive force of 

 the dry air in a change of temperature from 15°-7 to 41°*8 is 

 precisely as great as the increase in the expansive force of the air 

 and the aqueous vapour in a change of temperature from 15°* 7 

 to 30 o, 9 ; and this also agrees exactly, for the former increase is 

 calculated to be 0'119, and the latter amounts to — ■ 



For the air 0070 



For the vapour .... 0048 



Therefore, together . . 0*118 



In the second experiment we have the increase of the expansive 

 force 



For dry air, from 14°-4 to 44°-24 .... 0156 

 Then 



Forair, from 14°-4to31°-l 0076 



For vapour, from 14°'4 to 31°'l .... 0*052 



Therefore, together 0*128 



little differing from the preceding number. 



In order to obtain still greater certainty, I modified the expe- 

 riment in the following manner : — I gave the glass tube the 

 form represented in fig. 3, which differs from the form previously 

 used in this particular, that at k a globe is attached of about the 

 same size as the globe K ; moreover the vessel B B was filled with 

 pounded ice and water, so that the temperature was constantly 

 maintained at -f 0°*2. The results were as follows : — 



