96 
THE NATURE AND 
[sect. II. 
little, but not materially less, than that which would take place were it kept con 
stantly exposed to the sides. But to the convex surface the ends of the cylinder 
have to be added. 
With the addition of the ends to the surface, the quantity of cooling in degrees 
per second, (from art. 145.) becomes 
-07 (24 l + d) (T - t") 
d v 
where l is the length of the cylinder in feet, cl its diameter in inches, v the velocity 
of the piston in feet per second, T the temperature of the steam less sV part, and 
t" the temperature of the air. The force is reduced to 
( 4 \ 
1 — ^ ie f° rce 011 6 ie piston, as in art. 148. 
157. When low pressure steam is employed, the temperature T will be 212°» 
and putting — 60°, and supposing 
l = anc i v — 3-5 
12 ’ 
we shall have 
•07 (241 + d) (T - t") 
dv 
= 15'2 degrees ; 
and 
9-1 _ 1 
967 106 ’ 
Therefore in low pressure engines there is a constant loss for all sized engines of 
about Tiro of the power. When a casing is used and kept constantly filled with 
steam, the loss of heat and constantly of power from the same fuel will be greater; 
because the surface will be constantly kept at the temperature of the steam. I hope 
this will be sufficient to establish the truth, that the steam case is a useless addi 
tion to the expense of an engine. 
158. In a high pressure engine working at 300°, the loss by a naked cylinder 
is only about T5- part of the force. 
159. The best mode of preventing loss is to put a case with an air-tight cavity 
between it and the cylinder, instead of filling this case with steam; and besides the 
advantage of saving fuel the engine-rooms will not be heated so much. 
160. The single engine will lose more heat but not quite double the quantity 
of the double engine; hence we shall be about its amount in stating the cylinder 
at losing tV of the power. It will also lose double the quantity by the passage 
of the steam from the boiler to the cylinder. 
161. In atmospheric engines the loss of force by cooling in the cylinder, when 
a separate vessel is used for a condenser, is an interesting inquiry. Assuming that 
the piston is kept steam-tight without the use of water, the loss must be greater