[ *4 8 ] 
move freely, without touching the other. Thefe 
circles turn, each upon three friction pullies /*, n t 
and o y Oy o. The registers, which are very fiendcr. 
are counterbalanced by a fmall weight placed on 
the oppofite fide of the circle, and moved by a pin, 
which paffes through the index, and takes one along 
with it, as it moves one way, leaving it at the ex- 
treme point it has moved to, and, on its return, 
carries the other along with it, leaving it in the fame 
manner at the other extremity. The index and re- 
gifters are carried round the dial-plate very freely, 
by a weight of 8 grains. 
As this inftrument was intended only to mark the 
common degrees of heat and cold of this climate, 
which, according to Fahrenheit’s fcale, is feldom above 
80, or below o. I regulated its range by the following 
proportions, founded on Mr. Smeaton’s table of the 
expansion of metals, the experiments I had made on r 
fpelter and brafs correfponding pretty exactly. 
Greateft expanfion of the firft bar of fpelter from 
freezing to boiling water parts of an inch per 
foot, 2 feet long, x 3, the power of the fir Id 
lever, = 
2118 
10,000* 
Ditto of the fecond bar of hammered brafs, 2 feei 
•2 inches long, — — — -f x 3, the power 
o 10,000 ' 10,000 10,000 r 
of the fecond lever, nr 
7815 t 
io,ooo‘ 
Ditto of the third bar, 
5 ° 6 , 7815 __ 8321 
10,000 10,000 10,000 
2 feet 3 inches long, 
the power of the third 
33^84 
10,000’ 
Ditto 1 
