652 REGNAULT’S HYGROMETRICAL RESEARCHES. 
: External Psychrometer. Psychrometer in the apparatus. 
Aspirationswith) |/2i:2 01s) 3 oe cttett siti iy ee Sell pees hey ee a SS) 
t. wv. yee fe ‘A | v. | t—t/. if, 
‘———————— -—____—_ 
1843. June 11. ° ° ° mm ° ° ° 
1 Aspirator ...| 16°40 | 12-27 | 4-13 8-40 | 14:69 | 11°17 | 3-52 7-98 
2 cs evel 16-79 | 12°39 | 4°40 8°33 | 14:77 | 10°74 | 4:03 7°44 
18-15 | 13°34 | 4°81 8-69 | 14°80 | 11:17 | 3-63 7:92 
Air-pump...... 13:15 | 10°82 | 2°33 841 | 14:58 | 1052) 4-06 7:29 
2 Aspirators...| 16°10 | 13:48 | 2°62 | 10:09 | 14:85 | 12°57 | 2-28 9°62 
In this table it is seen that, when the current of air has been 
determined by the flowing of the aspirators, or by the air-pump, 
the elastic force of the vapour calculated with the formula, ac- 
cording to the observations made on the thermometers placed in 
the apparatus, was always less than that deduced from the ob- 
servation of the psychrometer placed out of doors: the contrary 
would certainly have taken place if the current of air had been 
slow. 
From all that has been said it results, that the agitation of the 
air must exert a very sensible influence on the indications of the 
psychrometer: it is easy to be convinced of this by a direct ex- 
periment. Let a psychrometer be fixed on the circumference 
of a horizontal wheel to which a very rapid motion is given. It 
is seen that, during the motion, the dry thermometer rises a small 
fraction of a degree, but the moist thermometer falls continually 
several tenths of a degree. 
I do not think that the fundamental hypothesis adopted by 
M. August can be admitted as basis of the calculation of the 
psychrometer; namely, that all the air which supplies heat to 
the moist thermometer falls to the temperature 7’ indicated by 
the latter, and is completely saturated with humidity. It seems 
to me probable that the portion of the air which cools does not 
fall to z', and that it is not saturated with humidity. The rela- 
tion of the quantity of heat which the air takes from the bulb 
by evaporation of the water, to the quantity of heat which it 
loses in cooling, is probably greater in proportion as that air is 
more dry, because, in this state, it is much more susceptible of 
humidity than when it approaches its state of saturation. 
Lastly, the temperature of the moist bulb is again otherwise 
influenced than by the immediately ambient air; it is subjected 
to the radiation of the chamber, the influence of which will be 
variable according to the state of agitation of the air. 
