134 GREAT MEN OF SCIENCE 



drive the air-blower of a blast furnace. It was a day of re- 

 joicing such as Watt had not known for long, when this success 

 was obtained, and the joy of his old friend Black, who had 

 always followed his work sympathetically, was also great. 

 The news of the engine's powerful and reliable action, and 

 its low consumption of fuel, soon spread, and the number 

 of engines built according to Watt's design continually 

 increased. Many coal-mines could only be operated at all 

 after Watt's engines were available to pump them dry, and 

 he himself was almost always obliged to supervise the in- 

 stallation in order to make sure of success. Only after six 

 years, 1782, did he find time to construct engines with 

 a rotating flywheel. It is noteworthy that he was 

 obliged to avoid the used of the crank already common to 

 every lathe, for converting the reciprocatory motion into a 

 rotary motion, and had to develop a special mechanism for 

 this purpose (the 'sun-and-planet gear'). Someone had 

 guessed Watt's intention, and obtained a patent for steam 

 engines with cranks. With the introduction of the flywheel, 

 the development of the engine on a large scale was completed, 

 and it remained without the addition of any new idea of 

 importance for over a century. For the high pressure 

 engine, the expansion engine, and the tubular boiler, had 

 already been thought of by Papin, Watts, and Boulton, and 

 the much deeper theoretical foundation later given by 

 Carnot and Robert Mayer, did not add anything essential 

 to the construction of the machine. Watt had at first 

 hesitated to suggest that even mills and other factories, which 

 were already in existence driven by waterpower, might go 

 over to steam and work on a much larger scale, but this soon 

 occurred, since coal, thanks to the pumping engine, could 

 be obtained easily and cheaply everywhere. The result 

 was a revolution in all mechanical factories, in particular a 

 very rapid advance in spinning and weaving, since it was 

 soon possible to employ hundreds of horsepower with 



