150 Report on Implements at Liverpool, and on 
safety and economy, suitability for most agricultural, and an 
infinite variety of other purposes." This is a startling pro- 
gramme, and it may be useful to inquire how it is to be accom- 
plished. The engine is constructed by Messrs. Crossley Brothers, 
Manchester. The principle and action of this remarkable engine 
are simple, but are not generally understood. The principal 
peculiarity of the engine lies in igniting the charge of mixed gas 
and air when this charge is compressed to a pressure of 30 lbs. or 
so above the atmosphere. It has been found that when gas 
and air are thus compressed, ignition is possible with a very 
much weaker mixture than when they are at atmospheric pres- 
sure only, the compression appearing to bring the particles 
within the range of chemical affinity. A weak mixture of gas 
and air thus ignited burns more slowly than one containing 
a higher percentage of gas, while the heat resulting from the 
combustion is imparted to the non-combustible portion of the 
mixture, expanding it and giving that sustained pressure on the 
piston, which has been an element so wanting in previous gas- 
engines. The following diagram and explanatory remarks are 
from the ' Engineer' : — 
Fig. 13. — Diagram from Otto's Gas-Engine. 
" It must be premised that the gas is only exploded once in every two ' 
revolutions when the engine is fully loaded, and the explosions may take 
place much more rarely when the engine is running against a small resistance. 
We have marked tlie diagram with letters and arrows to show the course of 
the i)iston. The first horizontal line is just below the atmospheric line, and 
marked A in the out stroke of the single-acting piston. The cylinder fills 
during this stroke with a mixture of gas and air through a slide-valve at tho 
back. The inward stroke is shown by B, which gives the curve due to the 
compression of the gas and air mixture. When the stroke is fiui.shed, the gas 
is ignited by a small gas-flame, and the pressure rises, partly as a result of 
the exi)losion, and jiartly because of the exjiansion of the nitrogen of the air 
due to the heat of the explosion. The piston then goes out, and the curve 
