[ 832 ] 
Divisions. 
Iron — — — — — — — — - 785 
Steel — — — — — — — — 6 95 
Note. Each divifion marks the 73,840th part of 
an inch expanlion per foot. 
I find that thefe come fomewhat near Mr. Smea- 
ton’s table. They are far from being as complete 
as I wifh ; but hope to be able to give a more ac- 
curate account hereafter ; as it certainly requires the 
natural cold to be added to the artificial, in order 
to get at the laft degree of the contraction of metals, 
which can be come at in this climate. 
If an inftrument of this kind fhould be deemed 
worthy the attention of the curious, there is no doubt, 
but it may be carried to a much greater degree of per- 
fection than this, which is but a rude beginning. The 
friction is little or none, as the l'pring at the top of the 
fourth bar, keeps the feveral levers and bars in the fame 
pofition on their axes, whether riling or falling. It 
may be made much more eafily, and at a lefs expence, 
by making ufe of counterballance weights, inltead of 
fprings ; and by a cord paffing over a pulley placed 
on the top of the fourth bar, with a weight fixed to 
it, which returns the bars, on their contraction. 
I have one making in this manner. The firlt bar of 
which is 3 feet long, and by a Aider, which is fixed 
by a fcrew, it will meafure the expan fion of any bar, 
within that length. The powers of the levers are 
all'o greater; and the minute hand goes 12 times 
round, for once the other goes round; by which it 
marks the 300,000 part of an inch expanfion per 
foot, and ranges a 16 inches, by the common degrees 
of heat and cold in this climate. 
* 
4 
Mercury 
