James Watt 103 



difficulty was overcome by some of the professors who 

 had recognized his ability before he went to London, and 

 established him as instrument maker to the University. 

 This gave Watt the opportunity of entering into intimate 

 scientific intercourse with such men as Joseph Black and 

 John Robison, and gaining a knowledge of the scientific 

 principles of heat. 



It was only in 1764, when a working model of one of 

 Newcomen's engines was sent to Watt for repair that his 

 mind was directed to the potential value of these machines. 

 Watt at once recognized the cause of the enormous waste 

 of fuel which constituted the chief defect of the engine. 

 When the steam introduced into the cylinder had done its 

 work by raising the piston, it had to be condensed before 

 the piston could return; this was done by a jet of cold 

 water introduced into the cylinder, which, of course, did 

 not only condense the steam but also cooled down the mass 

 of metal which formed the walls of the cylinder. When 

 the steam was reintroduced, the whole had to be raised up 

 again to the temperature of the steam before the piston 

 could be lifted. In order to avoid this waste of heat Watt 

 saw that the cylinder ought to be maintained permanently 

 at the temperature of the steam, and for this purpose it 

 became necessary to condense it, not in the cylinder itself, 

 but in another vessel, into which it had to be driven after 

 it had done its work. The invention of this separate con- 

 denser was Watt's first contribution to the steam engine. 

 He settled down in Birmingham with Matthew Boulton, 

 a capitalist, and gained experience in the manufacture of 

 his improved machines, which were still used exclusively 

 for pumping water. 



The next great step was made in 1782. Up to that date 

 steam was only admitted to the cylinder on one side of the 

 piston, the return stroke being made by the pressure of the 

 air against the vacuum formed by the condensation of steam. 

 Watt now invented the double-acting engine, in which 

 steam is alternately admitted and acts on both sides of the 

 piston. The third advance, which brings us still nearer to the 

 modern engine, is due mainly to the scientific knowledge 

 which Watt had gained of the properties of steam, investi 



