93 
Steam Engine. 
came associated in the prospects which it opened. But 
some of his own projects having failed, he soon after dis- 
posed of his interest to Mr. Boulton, the celebrated foimd- 
der of Soho manufactory, with whose aid Mr. Watt, in 
1774, solicited and obtained an act of parliament for the 
extension of the term of his patent for twenty-live years ; 
and the business of making steam engines was soon afte^ 
commenced by the firm of Boulton and Watt. 
In executing his invention on a large scale, Mr. Watt 
felt the necessity of improving the construction of seve- 
ral of the parts of Newcomen’s engine. With this view, 
he induced Mr. Wilkinson to erect an apparatus for bor- 
ing the cylinders with more precision than had hitherto 
been done ; he adopted a new mode of constructing the 
piston and screwing down the packing, and secured the 
rod in the piston in a more perfect manner ; he introduc- 
ed puppet valves into the steam boxes or nozles, instead 
of the old sliding regulators ; he used better means of 
opening these valves, and added various improvements in 
the working gear ; he suspended the working beam, so 
that the centre of motion was below the centre of gravity, 
instead of being above it, as in the old engines ; and he 
improved the mode of setting the boilers on the grates, as 
well as the apparatus for keeping the boilers regularly sup- 
plied with water. 
He introduced also into some of his earliest reciprocat - 
ing engines, the principle of using the steam to act ex- 
pansively, which he had discovered so early as the year 
1769.^ 
* This appears by a letter from him to his friend the late Dr. 
Small, of Birmingham, dated Glasgow, 28th May, 1769 ; of which 
the following is an extract. 
‘ I mentioned to you a method of still doubling the effect of 
the steam, and that tolerably easy, by using the power of steanl 
^ rusiiing into a vacuum, at present lost. This would do little more 
