( \t ) 
double, which is the moft valuable Confideration 
in an Engine, where the Pipes will fuftain fuch 
Force. 
Secondly , The Bores that carry off the Water from 
the Forcers are too fmall, there being (nearly) always 
two Pillars of 7 Inches Diameter, forcing into one Pipe 
of the fame Diameter, and 7 x 7 = 49 + 49 == 98. 
Therefore thofe Pipes of Conveyance fhould be near 
nine Inches Diameter. 
The Perfections of the Machine. 
The Timber-work is all admirably well performed, 
and the Corapofition and Contrivance, for Strength and 
Ufefulnefs, not exceeded by any I have feen. 
The caft Iron Cranks are better than wrought ones, 
by reafon they are very ftiff, and will not be /trained, 
but fooner break } but then they are cheap, and new 
ones eafily put in. 
The Wedge for putting on or releafing the Crank 
and Forcers, is better than the Hiding Sockets common- 
ly ufed. 
The forcing Barrels, Trunks, and all their Apparatus, 
are very curioufly contrived for putting together, mend- 
ing, altering or cleanfing, and fubjeft to as little Fridion 
as pofli'ole in that Part. 
The Machine for raifing and falling the Wheels is 
very good, though but feldom ufed, as they tell me j 
for they will goatalmoft any Depth of Water, and as 
the Tide turns, the Wheels go the fame Way with it. 
Thefe Machines at London-Bridge are far fuperior 
to thofe fo much famed at Marly in France , in re- 
gard the latter are very ill defigned in their Cranks, 
and feme other Parts. 
III. Epifiola 
