Agricultural Steam-engines at Newcastle. 
673 
capable of diminishing the range of temperature in the 
cylinder. 
The compound engine is such a device. Steam at the boiler 
pressure is first led into a small cylinder whence, after a moderate 
expansion, it exhausts into a larger cylinder, to be finally rejected 
into the air. At the presumed working pressure of 100 lbs., there- 
fore, and with a cut off at half stroke, steam, entering the small 
cylinder at 328°, would leave it, in accordance with Marriotte's 
law, at a pressure of 50 lbs., and a corresponding temperature 
of 280°, — the total drop of temperature in the high-pressure 
cylinder, where, as will presently appear, the losses due to 
cooling are greatest, being only 48°. Similarly, steam entering 
the large cylinder at 50 lbs. pressure, and 280° temperature, is 
rejected into the air at a pressure of 15 lbs., and a temperature 
of 212°, representing a drop of 68°. The total range of tem- 
perature is, indeed, the same in both these instances, viz. 116°, 
but the cylinders of the compound engine have, each, a mean 
temperature much nearer that of the steam employed in them 
than is the case with the cylinder of the simple engine. 
It is obvious from these considerations that a iurther advan- 
tage might be expected Irom leading the steam through a suc- 
cession of cylinders for the purpose of minimising the fall of 
temperature in each. A step has already been taken in this 
direction by the construction of triple-cylinder compound 
engines, and it is probable that a still larger number of 
cylinders might be advantageously used in large steam-engines. 
The leak of heat-energy which the Compound engine attempts 
to staunch has been discovered ; it remains to enquire how 
umch higher the ship will float after this leak has been stopped, 
or, in other words, " What percentage of advantage is there in 
Compound over Simple engines?" 
Upon this question the Newcastle trials have thrown new 
light. Hitherto, the performance of a Compound engine by 
one builder has been too often compared with that of a Simple 
engine by another maker, without greatly advancing the 
solution of the question. But, during the late trials, simple 
and compound engines by the same, and highly competent, 
designers, have, for the first time, competed with each other 
under precisely similar conditions. 
Three competitors, Messrs. Davey and Paxman, McLaren, and 
Foden, showed Simple and Compound engines at Newcastle, 
each of the very highest excellence, which, together, furnish a 
more conclusive answer to the question at issue than has ever 
before been obtained by the engineer. The following table 
exhibits the relative coal consumptions of these engines, and, 
