698 Report of the Consulting Engineers on the Trials of 
the steam as of its employment when generated. As regards 
tlie generation of steam, the proportion will depend on the 
temperature of the fire and on that of the escaping products of 
combustion ; while as regards the employment of the steam, the 
proportion will depend on the temperature of the steam as it 
enters the cylinder, and the temperature when it leavies it. 
In non-condensing engines, such as those under consideration, 
the temperature of the exhaust steam cannot be below 212° 
(leaving out of the question the use of a portion of this steam for 
heating the feed-water — which matter, however, involves a change 
in the physical condition of the agent) and, therefore, the only way 
to improve the proportion is to start with a higher temperature 
of steam. But the pressure of steam cannot be increased with- 
out a corresponding increase of temperature, and the advantage 
derived from using higher pressure steam is a consequence of 
its higher temperature. In the annexed Table VI., p. 727, 
the Reading Iron Works' Engine, tested at Cardiff, and the 
two prize engines and Mr. Foden's compound engine, tested at 
Newcastle, are compared. The third line gives the absolute 
temperature of the steam in each case ; the fourth line the fall 
of temperature, on the supposition that the steam leaves the 
cylinder at a temperature proper to 1 lb. back pressure, that is 
215° ; the fifth line is the quotient of the division of the fourth 
by the third, and shows the proportion of work to be expected. 
The sixth line is the reciprocal of the fifth reduced to one 
as the standard of the Reading Iron Works' engine, and repre- 
sents the proportion in which the steam should have been 
consumed, that being, of course, inversely as the amount of 
duty to be expected. 
We see that Messrs. Davey Paxman and Co.'s simple engine 
should have demanded about 7 per cent, less steam, and their 
compound 23^ per cent, less than the Reading Iron Works' 
engine. In reality their simple engine, as will be seen by 
the eighth line, took 13 per cent, less, while the compound 
took nearly 30 per cent, less than the Reading Iron VV'orks' 
engine. 
Considered apart from their boilers, it will appear that Davey 
Paxman & Co.'s Simple Engine and their Compound Engine 
each in round numbers exceeded by some 6 per cent, the duty 
which, having regard to the increase of the pressure of steam 
above that of the Reading Iron Works' engine tried at Cardiff, 
and taken here as a standard, would have led one to expect, 
while Mr. Foden's engine used an amount of steam which was 
about G per cent, more than the foregoing calculation antici- 
pated, so that his result fell a little below that of Davey 
Paxman's compound, working at 100 lbs. less pressure. 
