108 



and more water being occasionally poured on, this manipu- 

 lation was repeated until the mercury within came to be co- 

 vered by a film of water of about one-tenth of an inch in 

 thickness. The stopcock was now closed, and the appa- 

 ratus being lowered, the whole was left to itself until the 

 following day, when the first of a series of observations, con- 

 tinued for twenty successive days, was made, each compre- 

 hending the volume of the moist air, the pressure, and the 

 temperature both of the air and of the mercury in the baro- 



v' — V 

 meter. To deduce from these by the formula/ =: — -, — X p, 



the force of vapour, it was necessary, in the first instance, to 

 apply to ;:> all the corrections already explained, and in ad- 

 dition to raise 9ir64, the volume of the dry air, to what it 

 would be at the temperature and pressure of the moist air, 

 as noted in each observation. But, as this involved tedious 

 arithmetical computations, and as the thermometer during 

 the performance of the twenty experiments varied only 

 about 15°, I came to the resolution, being at the time upon 

 the eve of leaving town for a couple of months, to postpone 

 the calculations until I should be possessed of data applica- 

 ble to the solution of the problem I had undertaken, through- 

 out a more extended range of temperature. 



Accordingly, in November last, I resumed the subject 

 with the very same apparatus, which had been left statu quo 

 in the interval, and succeeded in completing a series of forty- 

 five additional observations, extending nearly as low as 32°, 

 and which I had every reason to expect would lead to satis- 

 factory results. Upon, however, submitting the whole to 

 calculation, I have been led to the mortifying conviction, 

 that in consequence either of the absorption of the oxygen 

 by the mercury and brass-work, or some accident which 

 befel the apparatus during my absence from town, the 

 entire of the latter series of observations is of no value, as 

 ihey lead to results for the force of aqueous vapour, which 



