250 EIGHTEENTH CENTURY. PT. ill. 



from the boiler will pass directly from e down to d, and 

 coming in below the piston, will drive it up again. In this 

 way, although the cylinder is never cooled, the piston 

 moves steadily up and down ; because the steam is driven 

 off into the condenser standing in B, where it is turned 

 into water, and is drawn up by the two pumps D and E, 

 and sent along the pipe, s, s, back to the boiler. 



This was the principle of Watt's double-acting steam- 

 engine, and if you understand the difference between Figs. 

 43 and 45, you will see that though Watt was not the first 

 to make engines move by steam, he was the first to make 

 a pure steam-engine, where the piston moves up and down 

 without any help from the outside air, or of the counter- 

 balancing weight e, Fig. 43, and without the enormous 

 waste of heat and fuel which made all the earlier engines 

 comparatively useless. 



I have only attempted to explain the way in which he 

 applied steam to his engines ; all the numberless other 

 improvements which he made must be studied in books on 

 engineering. For twenty long years he went on improving 

 and inventing without reaping any reward for his labour. 

 Other men tried to steal his ideas and to make a profit out 

 of his genius, and he had to fight against prejudice and 

 injustice, and against constant depression caused by his 

 own ill-health. Yet he found many kind friends upon his 

 road, and amongst the most famous of these was Boulton, 

 the Birmingham manufacturer, who became his partner in 

 1769, and stood by him manfully in all his difficulties and 

 troubles. It was from Boulton's manufactory at Soho (a 

 suburb of Birmingham) that Watt's engines went forth to 

 the world, and worked that great change in the manu- 

 factories of England which has made us one of the first 

 nations of the world. 



