190 
Steam Engine, 
before being allowed to expand, could rnamtaiii on each 
square inch of a safety-valve exposed to the atmosphere : 
for example, that masses or quantities of steam of the ex- 
pansive force of 20, 30, or 50 pounds the square inch of 
a common safety-valve, will expand to 20, 30, or 50 
times its volume, and still be respectively equal to the at- 
mosphere, or capable of producing a sufficient action 
against the piston of a steam-engine to cause the same to 
rise in the old engine (v/ith a counterpoise) of Newcomen, 
or to be carried into the vacuous part of the cylinder in 
the improved engines first brought into effect by Messrs, 
Boulton and Watt, 
In consequence of this discovery Mr. W oolf was ena- 
bled to use his steam tv/ice (if he chose), and with com- 
plete effect ; nothing more being necessary than to admit 
high steam, suppose of 40 pounds the square inch, into, 
one cylinder, to w’ork there by its expansive force, and 
then to allow the same steam to pass into, and expand it- 
self in, another cylinder of forty times the size of the first, 
there to work by condensation in the common way. Or 
'^vith only one cylinder, by admitting a proportionally small 
quantity of high steam into it from the boiler, Mr. Woolf 
found that he could effect a considerable saving in fuel. 
In this first improvement of Mr, W oolf, though the 
saving might be carried a considerable length, it was still 
necessarily limited by the strength of materials ; for in 
the employment of high steam there must always be some 
danger ©f an explosion, Mr, Woolf, however, by a hap- 
py thought, has completely obviated every danger of this 
kind, and can now take the full advantage of the expan- 
sive principle without the least danger whatever. This 
he effects by throwing into common steam the additional 
temperature necessary for its high expansion, ajter the 
steam is admitted into the ivoidnng cylinder^ which is heat- 
ed by metE.ns adequate to the end intended to be obtained ; 
