622 REGNAULT’S HYGROMETRICAL RESEARCHES. 
Let— 
t be the mean temperature of the air during the experiment ; 
J; the elastic force of the aqueous vapour in a state of saturation 
corresponding to that temperature ; 
i', the temperature of the aspirator at the end of the experi- 
ment ; 
j'; the elastic force corresponding to the vapour in a state of 
saturation ; 
H, the barometric height reduced to 0° at the end of the ex- 
periment ; 
a, the coefficient of dilatation of the air ; 
k, that of the sheet-iron ; 
V,, the volume of the aspirator at 0°. 
The volume of the aspirator at the temperature ¢’ will be 
V,(1+2/): that is the volume of the air aspirated when it fills 
the aspirator; but this volume of air is saturated with aqueous 
vapour; consequently the air alone, only supports a pressure 
H—/’; when this same air is in the cylindrical tube it exerts 
an elastic force H—/. Thus its volume is, in this last instance,— 
7.) 
Vo (1 +k’) — 
The temperature of this air is ¢ when it is in the cylindrical 
tube, 7’ when it is in the aspirator; consequently its volume, 
under circumstances identical to those which exist in the cylin- 
der, is— 
H—-/' l+et 
“H—f* 14+atl 
If we designate by » the weight of the cubic centimetre of air 
at O° and under the pressure of 0™760, and by 8 the density of 
the aqueous vapour taken in relation to that of the air, supposing 
that the vapour in a state of saturation in the air follows the same 
law of dilatation and of pressure as the air, we shall have for 
the weight of the vapour in this volume of air,— 
H—/f! l+at 1 bs 
Vo (1 +47’) . H—f peg © (1+at) 760° 
Equalizing this expression to the weights found by experi- 
ment, we obtain a series of equations by which we can determine 
8, and we may ascertain for certain whether that value is con- 
stant for all the temperatures. 
Vo (1+k2') 
I have preferred calculating by means of this formula the | 
weight of the vapour which must be in the air, supposing 
