REGNAULT’S HYGROMETRICAL RESEARCHES. 651 
value of ¢' corresponds to an infinite velocity of the current of 
air; but I am convinced, that by establishing through the appa- 
ratus a current of dry air more rapid than that which we have 
obtained in the preceding experiments (which is easily done by 
working A an air-pump), we see the temperature ¢’ of the moist 
thermometer fall very perceptibly below that which is deduced 
from the formula. I have in fact obtained in two experiments— 
: t’ calculated 
t. rie t—?’. by the formula. 
18°91 5°39 13752 bgt 
e295 oo 15°°60 8°00. 
The preceding experiments demonstrate that it is by a for- 
tuitous circumstance that the experiments of M. Gay-Lussac 
gave numbers differing little from those deduced from the for- 
mula; for very different numbers would have been obtained if 
another velocity of the current of air had been employed. The 
experiments of M. Gay-Lussac cannot consequently be cited as 
confirming the accuracy of the formula of M. August. 
If the velocity of the current exercises a great influence on 
the lowering of the temperature of the moist thermometer when 
the air is completely dry, it is evident that this influence must 
also be very sensible when the air contains a certain quantity of 
humidity. To convince myself of this, I made the following 
experiment :—The apparatus described above was put in com- 
munication by its tube E with an aspirator: to the extremity G 
a long glass tube was fitted, which drew the air from an outer 
court-yard, immediately by the side of a psychrometer. The 
aspirator was made to run, and when the moist thermometer had 
reached its stationary state, the two thermometers a and 6 of the 
apparatus, and the two thermometers of the external psychro- 
meter were noted simultaneously. As the same air acts upon 
the two psychrometric apparatus, it is clear that the formula 
applied to their simultaneous indications should lead to the same 
quantity of humidity. 
In a second experiment, to obtain a more rapid current of 
air, two aspirators were employed to aspirate at once; lastly, in 
a third experiment, a very rapid current was obtained by aspi- 
rating the air with an air-pump. ‘The following are the results 
obtained in this manner :— 
