d by weights on the
wheels to obviate a waste of power by yawing on the rails. The most
important expedient of all, however, lies in the establishment of a system
of registering the performance of all new engines, in order that
competition may stimulate the different constructors to the attainment of
the utmost possible economy; and under the stimulus of comparison and
notoriety, a large measure of improvement would speedily ensue. The
benefits consequent on public competition are abundantly illustrated by the
rapid diminution of the consumption of fuel in the case of agricultural
engines, when this stimulus was presented.

CHAPTER XI

OF VARIOUS FORMS, APPLICATIONS, AND APPLIANCES OF THE STEAM ENGINE.

In the English edition of this work, the first part of this chapter is
devoted to examples of Portable and fixed Agricultural engines, of
different makers and styles of workmanship, but not in sufficient detail,
nor illustrated on large enough scale to be of practical value as models,
forming rather in fact an illustrated catalogue of the manufacturer, than a
study for the mechanic. On this account, they have been entirely omitted,
and their place supplied by a few illustrations from American workmanship,
not only of Steam Engines, of various forms and applications, but also of
various machines, or appliances, connected with the working of engines, as
for the determination, or regulation of pressure, of the boilers; for the
supply or feed of the boilers, the regulation of the speed of the engine,
and the like.

The Gauges used in this country to show the pressures of steam in boilers
are of various constructions, but perhaps the most common is the Bourdon,
or, as it is known here, the Ashcroft gauge, from the party introducing it,
and holding the patent. Fig. 59 represents its interior construction. It
consists of a thin metallic tube, _a_, bent into nearly a complete circle
closed at one end, the steam being introduced at the other, at _b_. The
effect of the pressure of the steam on the interior of the tube is to
expand the circle, more or less according to the pressure, the elasticity
of the metal returning the circle to its original position, when the
pressure is removed. The free or closed end of the tube is connected by a
link _c_ with a lever _d_, at the opposite end of which is segmental gear,
in gear with a pinion, on which is a hand, which marks the pressure on a
dial. The dial and hand are not show