STEAM DETENTION. 405 



rupted, for example, when the piston has reached one 

 third of its course. The two remaining thirds of the 

 cylinder s length are then traversed by virtue of the ac 

 quired velocity, and especially by the detention of the 

 steam. Watt had already indicated such an arrange 

 ment.* Some very good judges esteem the economical 

 importance of the steam-detent as equal to that of the 

 condenser. It seems certain that since its adoption, the 

 Cornwall engines give unhoped-for results ; that with one 

 bushel of coals they equal the labour of twenty men 

 during ten hours. Let us keep in mind, that in the coal 

 districts a bushel of coals only costs ninepence, and ifc 

 will be demonstrated that over the greater part of Eng 

 land, Watt reduced the price of a man s day s work, a 

 day of ten hours labour, to kss than a sou (one half 

 penny^) of our nioney.f 



because the small portion of steam already admitted, then expanded 

 till the piston had reached the end of the cylinder. Translator. 



* The principle of the steam detention had been neatly expressed 

 in a letter from Watt to Dr. Small dated 1769, it was put in practice 

 in 1776, at Soho, and also in 1778 at the Shachvell water works, from 

 economical considerations. The invention, and the advantages ex 

 pected from it, are fully described in the patent of 1782. 



t At a moment when so many people are interested in direct rota 

 tion engines, I should be unpardonably neglectful if I did not say that 

 Watt had both thought of them, as proved in his patents, and had 

 made some. Watt abandoned those engines, not because they would 

 not work, but because, in an economical point of view, they appeared 

 to him decidedly inferior to the double-acting engines, and to those 

 with rectilinear oscillations. 



There are few inventions, large or small, amongst those of which 

 the steam-engine offers us such an admirable assemblage, that have 

 not been developed from some of Watt s early ideas. Follow up his 

 labours, and besides the important points which we have minutely 

 detailed, you will see him propose engines without condensation, 

 engines in which the steam, after having acted, is allowed to escape 

 into the open air, for those localities where it would be difficult to 

 procure an abundance of cold water. 



