158 Steam-Engine—Physics, §c. 
a state of water on losing its heat, by contact with any thing 
cold, Savary easily produced his vacuum by the injection of a 
little cold water. 
He also used (though in a very disadvantageous manner) 
ihe expansive force of steam to drive the water out of the 
chamber, through a pipe different from that by which it 
atered. 
It is doubtful whether this kind of engine was ever erected 
on a scale of any magnitude; for, afew years later, Newco- 
men and Crawley invented the first engine with a cylinder and 
piston ; and Savary, abandoning his own, united with them in 
bringing their engine into use. 
As steam drives out air, the principle of this engine was to 
let steam into the cylinder beneath the piston, where, (the pis- 
ton haying risen to the top of the cylinder) a jet of cold water 
condensed the steam, produced a vacuum, and the piston, 
working air tight, descended by the pressure of the atmosphere 
upon it, this pressure being a weight of nearly fifteen pounds f0 
each square inch; so that if the cylinder were two feet diame- 
ter, it would amount to a weight of three tons. 
This mode of operation prevailed for about fifty years, and 
though much used to pump water from mines, was found to 
have great inconveniences and defects ; till, in the year 1762, 
Mr. Watt, being employed to repair a working-model of i 
engine at the University of Glasgow, was led to direct his 
mind to the improvement of the machine ; and from his expe 
riments sprung the most essential change, viz. the condensa- 
tion of the steam in the cylinder, by opening a communication 
with a separate vessel, into which the injection of cold watet 
was made, thus allowing the cylinder to remain hot. 
On opening that communication, the steam instantly rushes 
to the cold, or rather is destroyed by the instant loss or reduc: 
tion of its heat, and the vacuum thus made allows the pis” 
to descend as before mentioned. 
* This jet of cold water being let into the cylinder itself, necessarily 
cooled it at every stroke; and then it was necessary to heat it again 
the boiling point, before the piston would reascend, and thus @ ¥ 
of heat occurred. Epzror, 
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