[ 28 ] 
but if the lever be pulled a little farther down than 
what is fufficient to lift the catch out of the teeth of 
the wheel, it will rub againft the edge of the wheel 
V, and thereby hinder the too quick defcent of the 
weight j and will quite flop the weight if pulled hard. 
And if the man fhould happen inadvertently to let 
go the lever, the elaific bar will pull it fuddenly up, 
and the catch will fall down into the wheel, and flop 
the machine. 
WW are two upright rollers, above the axis or 
upper gudgeon of the gib E : their ufe is to let the 
rope bend upon them, as the gib is turned to either 
fide, in order to bring the weight over the place to 
which it is intended to be let down. 
N. B. The rollers ought to be fo placed, that if 
the great rope were flrctched clofe by their outermoft 
fides, the half thicknefs of the rope may be perpen- 
dicularly over the center of the upper gudgeon of 
the gib. For then, and in no other pofidon of the 
rollers, the length of the rope between the pulley in 
the gib and the axle of the great wheel will be al- 
ways the fame, in all portions of the gib ; and the 
gib will remain in any pofition to which it is turned. 
When either of the trundles is not ufed in work- 
ing the crane, it may be drawn off from the wheel, 
after the pin near the axis of the trundle is drawn 
out, and the thick piece of wood is raifed up a little, 
behind the outward fupporter of the axis of the trun- 
dle. But this is not material : for, as the trundle has 
no fridion on its axis but what is occafioned by its 
own weight, it will be turned by the wheel without 
any fenfible refinance in working the crane. 
IV. 0/ 
