17 
of a new Pendulum . 
another, and in those cavities place two glass tubes, about two 
inches diameter, perpendicularly upwards, which may be done 
by various means ; and, while in this situation, having heated 
them gradually to the heat of melted lead, I should pour in 
melted lead, so as to fix them in their places when it cooled. 
The apparatus for fixing the point I, and that for fixing the tube 
I I, fig. 2 and 3 at F, fig. l, being also of brass, in heat they 
would always expand, and in cold contract, equally ; so that the 
glass tubes would keep always at an equal distance from one 
another, and equally perpendicular. Glass is not only very 
little apt to contract and expand by heat, but free from any 
such disposition from moisture or dryness, which is not the 
case with wood. 
Having added the apparatus I have described to Mr. White- 
hurst's machine, I set it a going, expecting, in the situation I 
placed it, only some approach towards accuracy in the length 
of the pendulum. I fixed beside it a transit which belonged 
to Mt.Ludlam, the principal parts of which were made by Mr. 
Ramsden, the object-glass was a four-feet focus achromatic by 
Dollond. I found my meridian mark at about three quarters 
of a mile distance. I likewise borrowed, from my friend Mr. 
Stevens, a clock with a gridiron pendulum, made by Graham 
for his father Dr. Stevens, in order to compare them toge- 
ther when I had no observations. There were several trivial 
circumstances, which baffled the experiments for some time, 
not worth relating, one only excepted ; which was, that the 
curvature of the wire, acquired by its being wound round a 
pirn, was not entirely unfolded for some months, so that the 
clock went slower and slower during that time. At length 
this difficulty was overcome ; I then began to observe with 
mdccxciv. D 
