103 
Steam Engine^ 
a square inch) will be accurately equal to the re-action of 
the water which is forced up ; and consequently, that Sa- 
vary’s engine will require steam more elastic than the air 
of the atmosphere, in every case except where the water is 
raised no higher than it can be by the vacuum that is pro- 
duced, and the pressure of the atmosphere. When the 
water is forced up through the rising-pipe, every square 
inch of the boiler must sustain a pressure equal to a co- 
lumn of water an inch square, and of the height of the 
pipe above the boiler. This, therefore, requires very 
strong vessels, and several accidents happen by their burst- 
ing wiien tile safety valve is loaded too much. 
But the greatest defect of this machine is the great waste 
of steam, and consequently of fuel. For when the 
steam is admitted to the top of the cold water in the re- 
it is condensed with great rapidity ; and the veatep 
does not begin to yield to its pressure, until its surface is 
so hot, as not to condense any more steam : it now de- 
scends ; but as by that, a new part of the side of the recei- 
ver is exposed to the steam, more is condensed, so that a 
condensation of the steam is going on all the while the 
water is descending. This too must necessarily be re- 
repeated every stroke, as the receiver is cooled every time 
it is filled with water. 
Mr. Savary succeeded in raising water to small heights^ 
and erected several engines in different parts of England ; 
but he could make nothing of deep mines. Many at- 
tempts have been made to correct these defects, but hi- 
therto without much success. 
In the beginning of the eighteenth century, Newcomen, 
an ironmonger or smith, and Crawly, a glazier at Dart- 
mouth, in Devonshire, first conceived the project of ap~ 
pljdng a piston with a lever, and other machinery. They 
were contented to share the profits of the invention with 
