[>82 ] 
cutting the line ef 3 as in k j this line may be fup- 
pofed to reprefent one of the levers turning upon 
its centre at g , h the point where the brafs bar 
adts upon the fhorter end of the lever, and k the 
point where the fcrew adts upon the longer end of 
the lever, which being the place where it inter- 
fedts the line ej, it is evident the ball of the pendu- 
lum will be as much raifed by the lever, as it would 
have been depreffed by the expanfion of the iron ; 
but the triangle i hg is fimilar to the triangle b gk- y 
and therefore, as i h, the excefs of the expanlion 
of the brafs, is to bg, the whole expanlion of the 
iron, fo will bg, the Ihorter arm of the lever, be 
to g k 3 the longer arm of the lever, 6). e. d. 
At Fig. i. is placed a ftrong double fpring, whofe 
ends preffing againlt the under edge of the ball, hin- 
der it from bending the brafs bar by its forcible 
adtion thereon at the point b 3 which, when the ball 
is of a conliderable weight, it might otherwife be 
very liable to do. 
The defcription here given is exadtly agreeable to 
the original contrivance ; and the only alteration I 
have lince made in it, confills in placing the fcrews 
gg within the ball of the pendulum, as reprefented 
in Fig. 4. 
But as the fuccefs of this contrivance depended 
intirely upon the fuppolition, that metals were ex- 
panded differently by the fame degree of heat, be- 
fore I attempted to put it in execution, I thought 
proper to inquire what experiments had already 
been made upon this fubjedt, when Mr. John Eames, 
a late very worthy member of this Society, put into 
my hands Mr. Graham’s account of his quicklilver 
pendulum 
