191 
Steam Engine, 
and the advantage which he thus gains he eiFectually se» 
cures by a most ingenious improvement in the piston. 
It may be easily conceived that steam of such high rarity 
as Mr. Woolf employ s, could not be made fully effective 
with the piston in common use ; for in proportion to its 
rarity so must be the facility with which a portion of it 
would escape, and pass by the side of the piston to the 
vacuous part of the cylinder i but Mr. Woolf’s contri- 
vance seems perfectly adapted to prevent the loss of even 
the smallest portion of the steam. 
Besides these improvements on the common steam-eip 
giiie, he has also found means to apply the same principles 
to the old engine, known by the name of Savary’s, in 
such a way as to render the same a powerful and econo- 
mical engine for a great variety of purposes. 
Such is the outline of Mr. Woolf’s improvements on 
this most useful engine : but, for the general information 
of practical engineers, we shall here subjoin a more tech- 
nical description, in Mr. Vvoolf’s own words, extracted 
from his specification of his patent. 
I have found out and invented a contrivancCj by 
which the temperature of the steam vessel or working cy- 
linder of a steam-engine, or of the steam vessels or cylin- 
ders where more than one are used, may be raised to aii}^ 
required temperature, without admitting steam from the 
boiler into any surrouiiding receptacle, whether known 
by the name of a steam case, or by any other denomina- 
tion. That is to say, instead of admitting steam of a 
high temperature into such receptacle or steam case, 
which is always attended wdth a risk of explosion propor- 
tioned to the elasticity of the steam employed, I put in- 
to the said surrounding receptacle, or case, oil or the fat of 
animals, or wax, or other substances capable of being melt- 
ed by a lower temperature than the heat intended to be 
employed, and of bearing diat heat without being convert- 
