C 488 3 
that I could perceive, by jerks. And I doubt not, 
but, when the point of bearing of the brafs bar upon 
the lever is once well adj ufted, it will be found to 
lengthen or fhorten the pendulum to as great a degree 
of exacftnefs, as any other method whatfoever. But, 
as I have not as yet thought of any other method of 
adjufting it, except from actual trial in different lea- 
ions of the year, I muft prefer the pendulum to this 
method, which, from the great eale, as well as ex- 
a&nefs, with which it is capable of being adjufted, 
will, 1 think, appear to have much the advantage 
over any other contrivance yet made ufe of for this 
method I take for adjufting the longer arms 
of the levers of the pendulum to the fhorter ones is 
delcribed in Fig. 4. To a ftrong poft, fixed to the 
wall, is faftened a fmall fhelf, lupported by two 
brackets a b. In the middle of this fhelf is faftened 
a wire, by the fcrew e ; to the end of which the pen- 
dulum is to be hung. Below this fhelf, at the di- 
ftance of about 40 inches, is placed the index c d , 
turning freely upon a center : The length of the in- 
dex is fo inches. At the diftance of half an inch, 
upon a part of the index produced beyond the centre, 
is placed a fteel pin ; and in the back of the pendu- 
lum, as near the centre of ofcillation as may be, is 
drilled an hole to receive this pin ; when the pen- 
dulum is hung upon the wire againft the poft, and 
the wire is fcrew’d higher or lower by the fcrew 
till the pin refting againft the upper part of the hole 
(which is filed into a proper fhape for that purpofe) 
keeps the index nearly in an horizontal polition. Be- 
low the bottom of the pendulum is placed a fecond 
index 
purpofe 
The 
I 
