( 40 ) 
IV. A Contrivance to avoid the Irregularities in a 
Clocl^s Motion y occaftond hy the Aliion of Heat 
and Cold upon the I^d of the Pendulum. (By 
Mr, George Grzh^imy Watch-'Makejy K S* 
W Hercas feveral, who have been curious in inea- 
furihg of Time, have taken Notice, that the 
Vibrations of a Pendulum are flower in Summer than 
in Winter; and have very juflly fuppofed this Alte- 
ration has proceeded from a Change of Length in the 
Pendulum itfelf, by the Jnhuences of Heat and Cold 
^ upon it, in the dilrerent Seafons of the Year^ with 
a View therefore of correcting, in fome degree, this 
Defect of the Pendulum, I made feveral Trials, about 
the Year 1715. to difeover whether there was any 
confidcrable Difference of Expaniion between Brafs, 
Steel, Iron, Copper, Silver, dv. when expofed to the 
fame Degrees of Heat, as nearly as I could determine j 
“conceiving it would not be very difficult, by making 
ufe of two Sorts of Metals, differing confiderably in 
their Degrees of Expanfion and Contradion, to reme- 
dy, in great mcafure, the Irregularities to which com- 
mon Pendulums are fubjeef. But altho’ it is eafily 
difcoverable, that all thefe Metals fuffer a fenfible Al- 
teration of their Dimenfions by Heat and Cold*, yet 1 
found their Differences, in Quantity from one ano- 
ther, were fo fmall, as gave me no Hopes offucceeding 
this Way, an.d made me leave off profecuting this Af- 
fair any farther at that Time, in the Beginning of 
'December,^ 1721. having Occafion for an exad Level, 
befdes other Materials I made Trial of, Quickfilver 
was one , which, although I found it was by no * 
Means proper for a Level, yet the extraordinary De- 
gree 
