50 
Steam Engine^ 
Tempe- 
Pressures given by 
Ano- 
rature. 
Experim. 
Calculus. 
malies. 
0 
0*00in. 
0*00in. 
0*00 
10 
0*47 
0*45 
-0*02 
20 
1*52 
1*56 
+0*04 
30 
3*49 
3*54 
+0*05 
40 
6*90 
6*97 
+0*07 
50 
13*05 
12*73 
-0*12 
60 
23*65 
23*05 
-0*50 
70 
37*30 
39*31 
+0*01 
80 
63*80 
64*35 
+0*55 
£0 
1 8*00 
98*23 
+0*28 
Thus the formula for the vapour of spirit of wine is 
found as simple as that for the vapour of water, without 
ceasing to represent the experiments with all desirable ex- 
actness, But more than this, we may retrench one of 
the variable terms ; for in the first degree has no 
greater value than OT'^, and when a: is 2, 3, or any other 
pv)siti •- e value, this third term may be safely neglected. 
The equation therefore is reduced to 
y=m^ ; 
a form much more simple than Bettancourt’s original 
equation, and indeed more simple than Prony’s improv- 
ed equation for the vapour of water. 
To save the trouble of investigating the strength of the 
vapour by these formula for every separate case that may 
occur, w^e add a table (calculated from these principles) 
in which the strength of the vapour both of w^ater and of 
spirit of wane is shewn for every degree of Reaumur’s 
thermometer up to 1 0^, or for every 2^ degrees of Fah- 
renheit, from 32 to 280® : the strengths are expressed, 
not in English or in French inches upon the barometer, 
but in terms, wdiose unit is the medium pressure of the at- 
mosphere, supposing that medium equivalent to 29*9 
