574 <S» george shuckburgh’s Obfervatiom 
APPLICATION. 
The height of the barometer in Englifh inches at any 
two places at the fame inftant, and the heat (according 
to Fahrenheit’s thermometer) to which it is expofed, 
being known, together with the temperature of the air 
at each place, obferved with a limilar inftrument; re- 
quired the difference of elevation of the two places in 
Englifh feet. 
RULE. 
Precept the iff, With the difference of the two thermo- 
meters that give the heat of the barometer (and which, 
for diilinCtion fake, I iliall call the attached thermome- 
ters^) enter table I. with the degrees of heat in the 
column on the left hand, and with the height of the 
barometer in inches, in the horizontal line at the top; in 
the common point of meeting of the two lines will be 
found the correction for the expanlion of the quicklilver 
(e) It is fcarce necelTary to remark, that, in order to make good conclufive 
obfervations, it is proper to be furnifhed with two barometers, and four ther- 
mometers; viz. one attached or inferted in the frame of each barometer; and 
the other two detached from them, in order to take the heat of the open air; 
for it will feldom be found, that the thermometer in the frame of the barometer 
and that in the air will Hand at the fame point, and for a very evident realon. 
