meafuring Heights with the Barometer. 757 
the manometrical experiments ; and the ratio of diminu- 
tion, in the temperature of 5 2 0 , hath been taken from 
the Peruvian obfervations, fuppofing it to decreafe uni- 
formly on each inch, or on the eight inches be- 
tween 29 and 21. For the fake of fimplicity, as well as 
from the want of fufficient data for afcertaining the 
lengths of the ordinates of the curve, the arithmetical 
hath been preferred to any progreffive diminution that 
might have been adopted, though by this mode the re- 
fults would have agreed better with fome of my own, as 
well as Mr. d e luc’s obfervations. In each of the co- 
lumns the equations for particular temperatures, com- 
pared with that for 12 0 or 92 0 , are reciprocally propor- 
tionable, fo that the maximum of the rate always cor- 
refponds to the fpace between 5 2 0 and 7 2 0 , as indicated 
by the manometer. It will be obferved, that though the 
equation in the table is only given for every io° of dif- 
ference of temperature, yet, by the intermediate rates for 
lingle degrees in the columns refpeclively, and the ratio 
of diminution for the height of the mean barometer 
above the fea, expreffed in that towards the right-hand-,, 
the equation for any particular temperature may be rea- 
dily obtained. The application of this table makes the 
third part of the rule, for meafuring heights with the 
barometer. When the mean temperature of the column 
