348 EXPLANATION OF THE PLATES. 
wheel on the crank shaft; and to reduce the friction its weight would cause, it is 
balanced by a heavy ball acting on a lever below it. 
Though the figures on the next plate are not a plan and section of this engine, 
yet the same parts, with the exception of the steam pipe, are nearly in the same 
places; and hence, by comparison of the two, the uses and action of the parts may 
be understood. 
The weight of an engine of this kind is not exactly proportional to its power ; 
but is nearly so ; and that of a forty horse power engine, with proper duplicate 
parts, water, and other appendages, is about 100 tons. See Section x.