r 5*? 3 
ones. In order to remedy this imperfection, the fame 
Mr. Huygens wrote a treatife, called Horologium of- 
cillatorium (a piece of geometry, which does honour 
to the lafl century), in which he demonflrates, from 
the properties of the cycloid, that the vibrations of* 
pendulum, moving in a cycloid, would be perform’d 
in equal times, even tho* the vibrations were un- 
equal. Pendulums therefore were made to vibrate in 
a cycloid; but great inequalities were Hill obferv’d in 
the motion of clocks. 
We do not read of any attempts, after this, to re- 
gulate the motion of clocks, till the year 1726, when 
Mr. George Graham deliver’d into the Royal Society 
a paper, which is publifh’d in the Phil. Tranf. N?, 
3 5? 2, in which he fays, that it having been appre- 
hended, that the inequalities in the motion of clocks 
arofe from a change of length in the pendulum, by 
the influences of heat and cold, he, about the year 
1715, made feveral trials, in order to difcover, whe- 
ther there was any conflderable difference of expan- 
flon between brafs, Heel, iron, fllver, &c. when ex- 
pofed to the fame degrees of heat ; conceiving, that it 
would not be very difficult, by making ufe of two 
forts of metals differing confiderably in their degrees 
of expanflon and contraction, to remedy, in great 
meafure, the irregularities, to which common pen- 
dulums are fubjeCt. He fays alfo, that, from the 
experiments he then made, he found their differ- 
ences fo fmall, as gave him no hopes of fucceeding 
that way, which made him leave off profecuting this 
affair any more at that time : That, fome time after, 
having obferved an extraordinary degree of expanlion, 
by heat, in quickfllver, he thought of a proper 
manner 
