meaf wring Heights with the Barometer. 759 
number of them correfpond to the fame thermometrical 
fpace. When the height is required in fathoms, the 
zero of Fahrenheit correfponds to -71.72, and the 
boiling point to +412.49: the fum of the two equa- 
tions 484. 2 t is the actual expanfion of common air from 
the heat of 212°. When the French toife is made ufe 
of as the meafure, the zero of the fcale hath been fhewn 
to coincide with 57°.i8 of Fahrenheit, or +n°j of 
reaumur. The negative equation i34°.72 anfwering 
to -14°^ of reaumur, and the pofitive 349°.49 cor- 
refponding to +8o°, or the boiling point, being added 
together, make again 484.21. 
In order to convey a more diftindt idea of the effedt 
which heat produces in the dilatation of different kinds 
of air, compared with quickfilver, along with the fcale 
for the equation I have placed another, expreffing the 
adtual and relative expanfions, refulting from the mean 
of the experiments, for every 20° of difference of tem- 
perature. This fcale is intended to give a comparative 
view of the manometrical with the thermometrical 
Ipaces, mentioned in the fecond fedtion. 
I fhall now clofe this paper, which hath already 
greatly exceeded the limits I wiflied to have been able to 
prefcribe to it, with a few remarks on the error of the rule, 
perceivable in the tables of computation, and the mea- 
Vol. LXVII. 5 E lures 
