to carried them into practical effect when he brought
out a new type of engine, with compression before ignition, higher
piston speed, more rapid expansion, and a general reduction of
dimensions for a given power. Due to this achievement, the cycle above
referred to has always been termed the "Otto" cycle.

CHAPTER II

THE COMPONENT PARTS OF AN ENGINE

Having recounted very briefly the chief points in the development of the
gas engine from its beginning, we may proceed to deal with matters of
perhaps more practical interest to those who we are assuming have had
little or no actual experience in making or working internal combustion
engines.

The modern gas engine comprises comparatively few parts. Apart from the
two main castings--the bed and cylinder--a small engine, generally
speaking, consists of four fundamental members, viz., the valves and
their operating mechanism, the cams and levers; the ignition device for
firing the charge; and the governing mechanism for regulating the supply
and admission of the explosive charge. There are innumerable designs of
each one of these parts, and no two makes are precisely alike in detail,
as every maker employs his own method of achieving the same end, namely,
the production of an engine which comprises maximum efficiency with a
minimum of wear and tear and attention.

Therefore, before dealing with each of these primary parts in an
arbitrary manner, and with the cycle of operations in detail, we propose
to make the reader familiar with the general arrangement and method of
working which usually obtains in the smaller power engines. In the
following illustrations these parts are shown. A (fig. 1) is the
ignition device which carries the ignition tube to fire the charge. H
and I (fig. 2) are the main valves, and GC (fig. 1.) is the gas-cock.
The side or cam shaft N (sometimes called the 2 to 1 shaft), the cams
which move the levers M, the latter in turn operating the valves, and
causing them to open and close at the proper time, are shown in fig. 11.
A bracket bolted up to the side of cylinder forms a bearing for one end
of the side shaft, and also carries a spindle at its lower end on which
the levers oscillate, transmitting the motion imparted to them by the
cams to the valves. The main cylinder casting and the bed need no
description. In some cases the bed is in two portions, though now a
great many makers are discarding the lower portion altogether, having
found