[ J 47 ] 
The fourth bar a moves upon two fmall pullies 
d, d, placed under it, and alfo a large pulley R, 
placed at the fide of the bar, towards the upper end. 
In each of thefe pullies, there is a deep groove for the 
bar to pafs freely, without touching the fides ; and 
on each fide of the groove of the pulley B, there is a 
channel cut for a thread to pafs, which is fixed to 
die fourth bar, by a hook at /, and has a weight 
fufpended at the other end. the thread placed in 
the inward channel, paffes alfo over a fmall pulley 
e 5 about 4 inch diameter, on the axis of which the 
index K is placed. The two weights g and h , fu- 
fpended to thefe threads, ferve as a counterballance 
to the fourth bar, and keep it in contact with the 
pulley B, which turns with the bar as it moves. 
Each of the levers is counterbalanced by a weight 
*, at the end of a thread, which paffes over a pulley 
pi placed above the lever, towards the end of its 
longer arm, and faftened to it by a hook at q. In 
adjufting thefe weights, it is neceffary, that each lever 
fhould preponderate a little towards the fhorter arm, 
in order to keep that end clofe to the bar placed on it. 
The counterballance weights of the fourth bar are fo 
much lighter, as to allow a fuperior gravity to the 
bar, fufficient to turn the index and regiftersj by 
which means, all the levers bear the fame wav, 
whether the bars are contracted or expanded. 
The axis of the fmall pulley /, on which the in- 
dex is placed, moves on friction wheels applied to 
each end. There are two regifters, or {lender hands, 
k, k y each of which is placed on a circle of brafs / 
and m, / about 2~ inches diameter, and m placed 
a little more forward than /, fo as to admit eacli to 
U 2 move 
