94 Steam Engine, 
The character of his engines being now fully establish- 
ed by the erection of several large ones in Cornw'aii, and 
other parts of the kingdom, Mr. Watt recurred to his fa- 
vourite idea of applying the power of steam to produce 
motions round an axis. 
He had, upon trial, found practical objections to the 
steam wheel described in his patent ; and a second one 
which he had contrived was also given up ; for, upon 
very full consideration of the subject, it appeared to him, 
that the object would be better attained by deriving the 
rotative motion from the rectilinear motion of the piston 
in the reciprocating engine. 
Something of this kind had been attempted by others. 
An atmospheric engine had been employed at Hartley 
coalery, in Northumberland, as early as 1768, to draw 
coals out of a pit. It had a toothed sector on the end of 
the working beam, working into a trundle, which, by 
means of two pinions with ratchet wheels, produced a ro- 
tative motion, in the same direction, by both the ascend- 
ing and descending stroke of the arch ; and, by shifting 
the ratchets, the motion could be reversed at pleasure. 
This engine had no fly-wheel, and went sluggishly and ir- 
regularly. Who the inventor tvas, we do not know. 
A patent was taken out in 1769, by a gentleman of the 
name of Stewart, for an engine which produced a rotative 
« than double the eiTect, but it would too much enlarge the vessels 
‘ to use it all. It is peculiarly applicable to wheel engines, and 
‘ may supply the want of a condenser where force of steam only is 
‘ used ; for, open pne of the steam valves, and admit steam until 
^ one fourth of the distance between it and the next valve is filled 
‘ with stea.m ; shut the valve, and the steam will continue to ex- 
« pand, and to press round tlie. wheel with a diminishing power, 
^ ending in one fourth of its first exertion. The sum of the series 
^ you will fiiid greater than one half, though only one fourth steam 
* was used. TliC power v/ill indeed be unequal ; but this can be 
« remevUed b<j g fiUi or other ’lyaysd 
