92 Ward's Steam- Engine. 
possesses momentum, and indeed, all the momentum, which 
the power of the steam could give it, inthe semi-revolution. 
Both of these assumptions, I undertake to deny. 
1. In their speculations on this subject, philosophers 
seem to have overlooked the mode, in which a steam-en- 
gine must necessarily be made, if intended for any useful 
purpose. Itis ofthe very essence of its construction, that 
not a particle of steam can enter the cylinder, when the 
crank is at the dead-point, cither on one side of the piston, 
or the other. And if there be no additional expenditure of 
steam, how can there be a further exertion of power? But, 
without resorting to this topic, is it not undeniable, asa 
general principle, founded in the very nature of things, that 
no power can be reversed, in its direction, as it is here, 
without first ceasing to act? And, as the power of steam 
is confessed to act, both before and after, the crank arrives 
at the dead-point; where else can it cease to act but at the 
dead-point, or which is the same thing, the point of its re- 
version ’—At the dead-point, therefore, the Engine must 
be perfectly impotent. 
2. The disproof of the second assumption seems to fol- 
low, asa corollary, from that of the first. It is acknowl- 
edged by all, that the reciprocating mass does stop at the 
dead-point; and what is this, but another mode of saying, 
that it has ceased to have Momentum ? 
If, then, the momentum of the reciprocating mass be not | 
overcome by the power of the steam, how, and by what, 
isit overcome? ‘The true explanation of these points will 
be found in the connexion of the fly-wheel with the recipro- 
cating mass, by means of the crank. Supposing no other 
inert body.to be connected with the Engine,—since we have 
just seen, that the momentum of the reciprocating mass 
cannot be overcome by the power of the steam, of course, 
there is nothing else which can overcome it, but the mer- 
tia of the fly-wheel. And the modus operandi, I take to be 
this :—The reciprocating mass and fly-wheel being con- 
nected through the medium of the crank, it results, from 
the principles of the crank, that the reciprocating mass is 
regularly and alternately accelerated, and retarded: ‘This 
retardation is gradual, and finally ends in total rest; after 
which the accumulation commences, and continues gradu- 
ally, until it arrives at its maximum. Now, during the re- 
