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Hiuft be made fo clofe, as to prevent the fpring from 
having any lateral motion in it. 
From this defcription it is evident, that, if the 
brafs bar expands more than the iron one, it will 
raife up the lever, and, confequently, the pendulum, 
which is faften’d to it; and, as the length of the pen- 
dulum is only from the centre of ofciilation to the 
under part of the flit, thro’ which the fpring pafles, 
the pendulum will be thereby fhortened; and, by 
making the point of the brafs bar to adt upon a pro- 
per part of the lever (to which it is capable of being 
adjufted by means of the fcrew d) the pendulum may 
be fhortened to whatever degree fhall be neceflary. 
To prevent the pendulum from bending the bars, 
which it would be liable to do, if the ball of the pen- 
dulum was of any confiderable weight, the end of 
the lever, fartheft from its centre of motion, is 
hook’d to the end of a chain, which is wound about 
and faftened to a fmall pulley at m. Upon the fame 
arbor, to which this pulley is fixed, is faftened an- 
other pulley, of a much larger diameter, to which is 
hung, by a filk line, the weight or counterpoife n. 
By means of this counterpoife, any part of the weight 
of the pendulum, that fhall be defired, may be taken 
off from prefling againft the brafs bar. And if, upon 
the end of the arbor, to which the pullies are fixed, 
an index be placed, fo as to point to a graduated cir- 
cle, the leaft motion of the lever will not only be 
eafily perceived, but alfo whether that motion is uni- 
form and regular, or not. And upon having, fome 
time after, made a clock with this contrivance added 
to it, I had the pleafure to find the index not only 
to move very fenfibly, but very regularly, and never, 
