566 
Mr. Lubbock on the Heat of Vapours, ^c. 
p'y ^ Ep' = 
ISK 
K 
a V {V + c) 
J 9 
Similarly, 
p y — Ep = — 
1 ^ IS 
ft a V (I + c) 
p a {I c) — p' a c 
ISKy 
ISK 
a V {I + c) (Jt> 
1 IS 
fjJ av (/' + c) 
liSK y XT 1 1 
- vE(l-y ) Nap.log^- 
Ep^ 
/ y 
y— ^ 
ll -Ep 
p a (I c) — p' a c — {p" -\-f) at 
yzl'] 
= a Rl 
- [4.-64ll966]^log* 
log<; 
2^1 
J 1 - jsy ! 
) y-J 
- Ep 
al(l -\-d) r 
\-Ep »■ 
If the machine work without expansion, 
y-i 
1 - £ y 
p=y, 
log 
V - (p" -I-./) 
1 + 8 
2^1 
1 J' J 
= 0 , 
The data upon questions relating to the steam-engine are the 
quantities a, I, V, S, and v, and it is evident that from these quan- 
tities the quantities ft and ft' may at once be found by an easy arith- 
metical operation; from these the following table will give the 
corresponding pressures p and p', and these pressures being in- 
troduced into equation A, the value of « r may be easily found. 
* Log. of Briggs, the pressure being reckoned in atmospheres, the log. of the con- 
stant is [7*9670537], the pressure being reckoned in lbs. per square foot. 
