44 HER OES OF INVENTION AND DISCO VER Y 



became very great after their engines were extensively adopted 

 This they very soon were, especially in Cornwall, where the 

 numerous mines afforded a vast field for the employment of 

 the new power, partly in continuing or commencing works 

 which only an economised expenditure could make profitable, 

 and often also in labours which the old engine was altogether 

 inadequate to attempt. 



But the draining of mines was only one of many applications 

 of the steam powLt now at his command which Watt contem- 

 plated, and in course of time accomplished. During the whole 

 twenty-five years, indeed, over which his renewed patent 

 extended, the perfecting of his invention was his chief occupa- 

 tion ; and, notwithstanding a delicate state of health, and the 

 depressing affliction of severe headaches to which he was 

 extremely subject, he continued throughout this period to per- 

 severe with unwearied diligence in adding new improvements 

 to the mechanism of the engine, and devising the means of 

 applying it to new purposes of usefulness. He devoted, in 

 particular, the exertions of many years to the contriving of the 

 best methods of making the action of the piston communicate 

 a rotatory motion in various circumstances, and between the 

 years 1781 and 1785 he took out four different patents for 

 inventions having this object in view. In the midst of these 

 scientific labours, too, his attention was much distracted by 

 attempts which were made in several quarters to pirate his 

 improvements, and the consequent necessity of defending 

 his rights in a series of actions, which, notwithstanding suc- 

 cessive verdicts in his favour, did not terminate till the year 

 1799, when the validity of his claims was finally confirmed 

 by the unanimous decision of the Judges of the Court of 

 King's Bench. 



