662 On Compound Engines for Agricultural Purposes. 
one behind the other (commonly called the tandem arrange- 
ment), and a single slide-valve, generally more compact, and 
with fewer working parts than the above, but probably less 
economical in fuel. Alongside these engines they showed a 
16-horse-power horizontal stationary compound engine of the 
same type as their 10-horse-power portable. 
Messrs. Burrell exhibited an 8-horse-power compound traction 
engine, with two cylinders, one single and the other double- 
acting, placed tandem, with single slide-valve. 
At Messrs. Fowlers' stand was a 16-horse-power semi-portable 
compound engine, of the same type as theirs at Kilburn, with 
two cylinders side by side, and cranks at right angles beneath 
the boiler, an arrangement which is well adapted for winding 
and other purposes, where it is desired to fix an economical 
engine quickly, without expensive foundations. They also 
brought to Derby a compound traction engine, which was seen 
by those who visited their plough-field, but which was unfor- 
tunately too late for the Show itself. 
Messrs. Aveling and Porter showed a compound tramway 
engine, with two tandem cylinders and single slide-valve, 
arranged in a peculiar manner in accordance with the patent 
of Mr. Kingdon of Torquay, who has adapted the same type of 
engine with advantage for driving small steam-launches. 
The object of the present article is not so much to describe 
in detail the engines already exhibited, as to lay before those 
readers of the ' Journal ' who are steam users but not engineers 
themselves, the salient features and advantages of the compound 
system in steam-engines ; and so to enlist their interest at once 
in the probable rapid adaptation of the principle to agricultural 
engines. 
In an ordinary high pressure steam-engine the piston is 
propelled from end to end of the cylinder, by the excess of the 
pressure exerted on the one side of it, over the resisting 
pressure of the exhaust on the other. At a certain part of its 
stroke, the connection with the boiler is shut off, and the 
volume of steam contained in the cylinder then expands, re- 
ducing its pressure at the same time, but still propelling the 
piston forward, till on arrival at or near the end of the stroke, 
the slide-valve opens its exhaust port, which permits the steam 
to escape into the atmosphere (generally with some noisy 
report), during the return stroke, while steam is admitted to the 
opposite side of the piston. 
With a single eccentric and slide valve, the connection with 
the boiler is usually shut off when three-fourths of the piston 
stroke has been accomplished, and the steam expands during 
the remaining fourth of the stroke, giving with 75 per cent, of a 
