Cm) 
Fri&ion they would have been fubjedl to, by moving 
in Holes. A Brafs Semicircle was provided, and 
from the lowed Point graduated each Way, and a few 
of the Degrees, about that Part of it which anfwer’d 
to the Dip, were divided into fix equal Parts. By 
the Help of Screws, the Semicircle could be brought 
to a due Situation \ and by two fpirit Levels, placed 
at right Angles to each other, any Ch?nge of Situation, 
was eafily perceiv’d, and by the Screws it could be 
readily refior’d to its former Polition } all was inclos’d 
with Glafs to fecure the Needle from being difiurb’d 
by the Motion of the Air. I mufl here take Notice 
of the great Difficulty there is of pcifing the Needle 
fo exa&ly, before it is touch’d with the Loadftone, 
as to take any Pofition indifferently: for, when it is 
pretty near the Truth, it is extremely troubiefome to 
place it at reft in the Pofition defir’d, in order to try 
which Way it is inclin’d to move. It cannot be done 
in the open Air j for the lead Motion of it will difturb 
the Needle, and when it is (hut up, it is no eafy 
Matter to fettle it in the Place intended. And that 
there will be a f nfibie Difference of the Dip, upon 
(hifting the Sides of the Needle, whatever Pains be 
taken to prevent it, I am fully (atisfied from tire fol- 
lowing Experiments. 
, 
March 2Q, 1732. 
EXPERIMENT I. 
I Touch’d both Sides of that End of the Needle’ 
which I defign’d to point South, upon the North- 
pole of a fmall Terr ell a , after which I caufed it to vi- 
brate in an Arch of ten Degrees, and counted the 
Time by a Pendulum Clock, (hewing Seconds till 
the Needle had performed 50 Vibrations. 
A a a 2 
It 
