chapter is to give the novice a complete insight into the various parts of a petrol engine, and their respective functions.

What is a Petrol Engine? — 'Petrol Engine' is a slang term for an engine driven by a series of explosions of a mixture of the vapour of a light spirit of petroleum with air.

'Gas engines' are similarly driven by explosions of a mixture of coal gas and air.

Both are known as 'internal combustion engines.'

In order to explain the system, there is here taken as an example a single-cylindered engine of the Daimler type.

Fig. 1 represents a drawing of such a motor if it be cut in half; fig. 2 the same motor cut in half the other way through.

p is a piston which accurately fits in a cylinder, and is free to pass up and down the interior of same. The top of the piston travels between the dotted lines at the top, t, and the dotted line