572 HISTORY OF THERMOTICS. 



laws operated in a practical form. James Watt, the 

 main improver of that machine, was thus a great 

 contributor to speculative knowledge, as well as to 

 practical power. Many of his improvements de- 

 pended on the laws which regulate the quantity of 

 heat which goes to the formation or condensation 

 of steam, and the observations which led to these 

 improvements enter into the induction of latent 

 heat. Measurements of the force of steam, at all 

 temperatures, were made with the same view. 

 Watt's attention had been drawn to the steam- 

 engine in 1759, by Robison, the former being then 

 an instrument-maker, and the latter a student at 

 the University of Glasgow 14 . In 1761 or 1762, he 

 tried some experiments on the force of steam in a 

 Papin's Digester 15 ; and formed a sort of working 

 model of a steam-engine, feeling already his voca- 

 tion to develope the powers of that invention. His 

 knowledge was at that time principally derived 

 from Desaguliers and Belidor, but his own. experi- 

 ments added to it rapidly. In 1764 and 1765, he 

 made a more systematical course of experiments, 

 directed to ascertain the force of steam. He tried 



14 Robison's Works^ vol. ii. p. 1 13. 



15 Denis Papin, who made many of Boyle's experiments for 

 him, had discovered that if the vapour be prevented from rising, 

 the water becomes hotter than the usual boiling-point ; and had 

 hence invented the instrument called Papin's Digester. It is 

 described in his book, La maniere d'amolir les os et de faire 

 cuire toutes sortes de viandes en fort peu de temps ct a pen de 

 frais. Paris, 1682. 



