[ i6 2 ] 
in proportion to the diameter of the cylinders they 
work in. That of the plug frame, which is a piece 
of timber moved by the leaver through a wooden 
groove, by which the fleam valve, and injection cock 
are opened and fhut alternately, is pretty considera- 
ble ; but the quantity proceeding from the feveral 
parts cannot be eftimated with any tolerable degree 
of precifion. 
The whole weight to be raifed, as alfo the fuperi- 
or power by which it is raifed, center in the pevets 
of the axis of the great leaver, and the quantity of 
fri&ion in the pevets, may be deemed equal to half 
fo much weight hanging on them. 
In order to form fome eflimate of the quantity of 
weight with which the axis of the leaver of a fire- 
engine is loaded, I took the dimenfions of the feve- 
ral parts of that at the York-Buildings water-works j 
the leaver of which is 27 feet long, 2 feet 6 inches 
by 2 feet 2 inches in the middle, and 2 feet by 22 
inches at the ends. The weight of which, with the 
archeads, chain, rods, and working frame hanging 
at one end, and the pifton and chain at the other, 
may be computed at 6 tons, or 12,000 pound. The 
cylinder is' 45 inches diameter, about 1591 fquare 
inches ; which, at 15 pound per inch prefiure of the 
atmofphere, is 22,274 pound. The pillar of water 
to be raifed is 10,060 pound, which is not 6 4 pound 
per inch ; fo that the remainder of the power is em- 
ployed in overcoming the refiftance from fridhon in 
,the feveral parts of the engine, and giving the leaver 
a degree of velocity equal to 120 feet per minute, 
•which it moved in common work. 
The 
