402  W. A. Norton on Ericsson's Caloric Engine. 
; k ‘ 
k will be reduced to 5 but the mean effective pressure for the 
same fractional stroke 6, when the cut off a is used, will be greater 
than this, and the actual pressure after the expansion to }, will be z 
So that the constant pressure for the b cut off is equal to the 
pressure for the a cut off reduced by the expansion to 6. : 
It may be well to inquire, in this connection, into the proper 
relative size to be given to the supply and working cylinders to 
obtain the greatest amount of motive power from the engine. 
Let A = area of supply piston, and 2 = ratio of working to sup- 
ply piston; then, by what we have seen, the portion of the stroke 
during which the air is flowing into the working cylinder, and 
acting with its full constant pressure is equal to Pi Calling 
this pressure per square inch, P, the following proportion gives us 
the mean. effective pressure (p) on working piston, for the whole 
stroke, viz., :hyp. log. z+1::P: spol) 1 Fats The meant 
£ 
effective upward pressure upon the whole piston will therefore be 
P log. +P 
expressed by xAz, or P.Alog.z+P.A. The down 
ward pressure on the working piston = 151bs. x Az, and hence 
the resulting effective pressure = P.A log. ¢4+-P.A —15Az. With 
the aid of the differential calculus, we find this expression to be 
a maximum when @=F5, (more accurately a3) from which 
from 
The 
This would make the radius of pate 
t. It was Ericsson’s original design ‘4 © 
t eae f the ealori¢ 
, set US See Now how the power of the engines of he *® 
ship is to be determined. tthe ae & press ures upon the t 
lta pressure of 12 Ibs. instead of 8 Ibs. were used, the 
a 
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