361 
Steam Engine* 
|21 1-8 X 21 1-8), the product will give 446 1-4 round 
inches for the whole surface : and S meat on reckons the 
effective or working pressure per round inch on the at*- 
iiiospheric engine, at seven pounds avoirdupois. It is 
usual to reckon the working pressure on a close engine 
(like that in question), at 10 pounds the round inch ; but 
I shall first take the seven pounds as being against the 
builder : So that, by multiplying the round inches 446 1-4 
by 7, we have 3:23 3-4 pounds for the weight raised» 
But the strokes are 23 of four feet double per minute, 
that is to say, 184 feet. Multiply the weight 3123 3-4 
by the height 184, and the product 574760 will be the 
mechanic effect of the engine, or the number of pounds 
it will raise one foot high in one minute. Lastly, divide 
this by Boulton and Wattes horse-power (^ |m ), and the 
quotient 17-^, or very nearly 18, will express the power 
of the engine in horses. 
If we follow Desaguliers, the engine will prove equal 
to 21 horses. 
And, according to Smeaton, its power will be equal to 
25 horses. 
If we had taken the pressure at 10 pounds per round 
inch, the powers w^ould have proved much greater, as 
below. 
In the above calculations the horses are supposed to be 
fairly worked, and the engine is supposed to be stopped 
as soon as the horses leave off. But an engine can work 
the whole 54 hours ; and Smeaton, considering that three 
setts of horses must be kept to work constantly for the 
same time, reckoned a steam engine to be equivalent to 
three times as many horses as could equal its rate of work- 
ing. The following table will shew the powers of thk 
engine, according to all these several methods r 
