of a new Pendulum. ig 
viz. instead of grinding the two crystalline pieces in a cylindric 
form, the lower part should be ground in a cycloidal form ; 
then it would have the advantage of cycloidal cheeks, which 
no contrivance hitherto has been able to attain. 
There are some farther observations necessary to be made, 
to enable workmen to construct clocks according to this prin- 
ciple, and some reflections upon its operation. 
The manner of hanging a leaden weight to the pendulum, 
its proportion to the maintaining power, the manner of apply- 
ing the pendulum to the clock, and the structure of the clock, 
aretobe found in Mr. Whitehurst’s pamphlet; with only 
this difference, that the steel wire should ga through a tube 
placed in the axis of the spherical lead weight, and be fixed at 
the bottom instead of the top of it. This, however, is of no 
great consequence if there be a power of altering the height of 
the fixed point I, fig. 1 ; because Mr. Whitehurst’s pendu- 
lum consisting partly of steel, partly of lead, therefore the point 
I must be adjusted to the joint expansions of lead and steel, if 
the wire be fixed at the top of the ball. 
The first reflection that I shall make is, that the steel wire, 
the brass tube, and the materials which connect the points I E, 
being of different sizes, and different in their disposition to be 
heated or cooled, some one of them might be heated or cooled 
faster than another. But where good clocks are kept, the 
changes of the heat of the atmosphere are so slow, that no 
great difference can take place in the time that each of the 
parts rises to the heat of the atmosphere in the room where 
the clock is kept ; none that could make any sensible error. 
As the difference of the time when they acquired the heat, 
would be compensated by the difference of the time when they 
Da 
