REGNAULT’S HYGROMETRICAL RESEARCHES, 649 
would become independent of the absolute velocity of the cur- 
rent of air,—a consequence to which we are naturally led by the 
reasoning applied by M. August to the calculation of the for- 
mula of the psychrometer. 
With this view I arranged the apparatus as follows :— 
A dry thermometer a and a thermometer with a moist bulb 4, fig. 
10, are placed in two cylindrical very thin brass boxes A and B. 
The bulb of the thermometer 6 is covered with a piece of cam- 
bric, which is continually kept moist by a cotton wick which is 
immersed in a small vessel c, containing water, and whose neck 
is hermetically cemented into the lower tubulature of the box B. 
A brass tube bent several times E F G,is put in communication 
with a large tube full of pumice-stone moistened with sulphuric 
acid to dry the air perfectly, and the tube D communicates with 
an aspirator of considerable capacity. The experiments were made 
in the laboratory of M. Reiset, with two aspirators, each of 600 
litres in capacity, and which were so arranged that they could 
aspirate separately, or both at the same time in the same space. 
The apparatus was placed in a large glass bell filled with water 
at the ambient temperature, and which was continually agitated. 
The dry air, before reaching the thermometer a, had traversed a 
very long metallic tube G F E plunged into the water of the vessel, 
and had acquired the temperature of that water; the latter was 
moreover very near to the ambient temperature. The stopcock 
of one of the aspirators was opened partially, the moist thermo- 
meter fell immediately; at the end of some time it became 
stationary: the temperatures indicated by the two thermo- 
meters were then noted. To obtain the velocity of the cur- 
rent of air, the water which flowed from the aspirator was re- 
ceived into a glass balloon, having a mark on the neck, and 
which indicated 5 litres. The number of seconds which the 
vessel took to fill was counted by a watch marking seconds ; it 
was easy to deduct from this observation the number of cubic 
centimeters run off in a minute. r 
A new determination was made exactly in the same manner, 
opening the stopcock more, and so on. To obtain a very rapid 
flow, the two aspirators were made to run at once. 
The following are the results which were obtained :— 
