[483] 
pendulum (as it is now commonly called) published 
in the Philofophical Tra?ifa£lions y N° 392, which 
account I found to be introduced by the following 
paragraph : 
u Whereas feveral, who have been curious in 
“ meafuring of time, have taken notice, that the vir 
a brations of a pendulum are flower in fummer than 
in winter; and have very juftly fuppofed this al- 
ct teration has proceeded from a change of length in 
<c the pendulum itfelf, by the influences of heat and 
a cold upon it, in the different feafons of the year ; 
“ with a view therefore of correcting, in fome de- 
<c gree, this defeCt of the pendulum, I made feve- 
u ral trials, about the year 1 7 1 y, to difcover whe- 
cC ther there was any confiderable difference of ex- 
f< panflon between brafs, fleel, iron, copper, filver, 
<c &c. when expofed to the fame degrees of heat, 
as nearly as I could determine; conceiving it would 
“ not be very difficult, by making ufe of two forts 
u of metals differing confiderably in their degrees of 
“ expanflon and contraction, to remedy, in great 
a meafure, the irregularities, to which common pen- 
tc dulums are fubjeCt. But although it is eaflly dif- 
u coverable, that all thefe metals fuffer a fenflble 
alteration of their di mention by heat and cold ; 
“ yet I found their differences in quantity, from one 
“ another, were fo fmall, as gave me no hopes of 
tc fucceeding this way, and made me leave off pro- 
“ fecuting this affair any farther at that time.” 
The reading this paragraph proved at that time 
fuflicient to make me lay aflde all thoughts of fuc- 
ceeding in a contrivance founded upon principles, 
which a gentleman of fo great abilities, and known 
P p p 2 accuracy 
