108 Sullivan on the Revoloing Engine. 
from the original power, arises from the friction of the ma- 
chine only—which point we will consider after a moment’s 
attention to the nature of force. 
Force is known and measured only by its effects. 
If a machine is so constructed as to render gravitation, at- 
mospheric pressure, or the expansion of elastic fluids, ope- 
rative, continually ; then the machine will be more or less 
perfect, as it consumes on itself, the power from these sour- 
ces, in transmitting it to its object. 
But as in estimating these sources of power, time is a ne- 
cessary circumstance; the constant transmission of the power 
by the machine, will enter into the estimate of its quality. 
And if, as in the common steam engine, the atmospheric - 
pressure is not constant, or if being so, the manner of convey- 
ing it is not constantly the same, it may be said to be a loss of 
power only because it is a loss of teme, in which, were the 
machine otherwise constructed, the power might have been 
exerted. 
Your correspondent misleads the mind by the terms in 
which he states, that ‘‘ he proposes to examine what portion 
of the force applied to give the alternating motion of the- 
piston is actually employed in producing the rotary move- 
ment of the cylinder, and what portion zs lest to all useful 
purposes.” 
And he thinks, “‘ when the piston is in a line with the 
two centres,” (or is proped for the moment, by the fixed 
crank) “that the whole force employed to raise or depress 
the piston is entirely lost.” 
We have anticipated the first point by reference to Young; 
—and need only add, that it is unnecessary to investigate 
what is an already received and established rule, that the 
difference of advantage between a force acting constantly at 
tight angles with the crank—and obliquely ata ie be 
angle as “usual, is as 7 to 11. 
As to the second, it may be said there could be no power 
m question, but through the intervention of the machine, 
and if the operation of “the machine is suspended in the po- 
sition supposed, there can be no power to loose—but your 
correspondent carries his idea of the practical effect of the 
principle of resolution of forces to an extent, that militates 
with some received principles of mechanics. He assumes 
asa given quantity 200. ‘ This force will resolve itself 
