193 
Steam Engine, 
mitted into the steam vessel or vessels, all the effects that 
can be obtained from steam of a high temperature, with- 
out any of the risk with which the production of the lat- 
ter is accompanied, not only to the boiler and other parts 
of the machinery, but even to the lives of the workmen ; 
for such low steam, or even water, (but in every case 
steam is preferable,) being admitted into a steam vessel 
or vessels, or working cylinder or cylinders, kept at the 
requisite higher temperature by the forementioned means, 
v/ill there be expanded in any ratio required, and produce 
an effect in the working of tlie engine which cannot other- 
wise be obtained but at a greater expense of fuel, or with 
the risk of an explosion. By this means I can make use 
of steam expanded in any required ratio, or of any given 
temperature, without the necessity of ever having the 
steam of any greater elasticity than equal to the pressure 
of the common atmosphere. 
‘‘ Another improvement which I make use of in steam 
engines consists in a method of preventing, as much as 
possible, the passage of any of the steam from that side 
of the piston which is acted upon by the said steam to 
the other side which is open to the condenser ; and this 
I effect, in those steam engines known by the name of 
double engines, by employing upon or above the piston 
mercury or hiiid metal, or metals in an altitude equal to 
the pressure of the steam. The efficacy of this arrange- 
ment will appear obvious, fi'om attending to what must 
take place in working such a piston. When the piston 
k ascending, that is, when the steam is admitted below 
the piston, the space on its other side being open to the 
condenser, the steam endeavouring to pass up by the 
j side of the piston is met and effectually prevented by the 
I column of metal equal or superior to it in pressure, and 
I during the down stroke no steapi can possibly pass with- 
j Qut first forcing ail the metal through. In working what 
i VoL IL B B 
