107 
Steam Engme. 
By the admission of the steam under the piston, the 
pressure of the atmosphere on the top is counterbalaacedj 
and the piston is free to move upwards or downwards. 
But the other end of the beam being broader, so as to 
be heavier than the piston, now raises it to the top of the 
cylinder, whence it is again forced downwards by the pres- 
sure of the atmosphere, as soon as a vacuum is formed 
under it by the admission of the injection- water. In this 
manner the operation is repeated ; the piston being forc- 
ed down by the weight of the atmosphere, raises the 
other end of the beam, with whatever is attached to it ; 
and, on the other hand, when the pressure of the atmo- 
sphere is counterbalanced by the steam under the piston, 
the superior weight of the pump-end of the beam briiigs 
the piston up again. 
We now see the difference between Savarv’s and New"» 
comen’s engine, in respect to principle. Savary’s was 
an engine that raised water by the force of steam ; but 
Newcomen’s raises water entirely by the pressure of the 
atmosphere ; and the steam is employed merely as the 
most expeditious mode of producing a vacuum, into 
which the atmospherical pressure may impel the first 
mover of his machine. 
We see also the great superiority of this new machine. 
We have no need of steam of great and dangerous elastici- 
ty ; and we operate by means of very moderate heats, and 
consequently wdth a much smaller quantity of fuel : and 
there are no bounds to the power of this machine. How 
deep soever a mine may be, a cylinder may be employed 
of such dimensions, that the pressure of the air may ex- 
ceed in any degree, the weight of the column of water to 
be raised. And lastly, this form of the machine renders 
it applicable to almost every mechanical purpose ; be- 
cause a skilful mechanic can readily fitid a method of 
converting the reciprocating motion of the working- beam 
