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 it 
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 less than a sou (one half- 
penny,) of our money. 
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 Shadwell water works, from 
economical considerations. The invention, and the advantages ex- 
pected from it, are fully described in the patent of 1782. 
7 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. 
