[ l6 5 ] 
will be generally final], and the correction to re- 
duce one barometer to the heat of the other will 
confeq'uentiy be fmall alfo; whereas the difference 
of the prefent heat, and the fixt temperature, and 
confequently the correction of both barometers, 
may be frequently very confiderable : this is 
evident : becaufe if the heat of the barometers, at 
both ftations, was the fame, however different from 
the fixt temperature chofen by M. de luc, no 
correction would be neceffary ; the mercury in the 
barometer in both ftations, being expanded in the 
fame proportion, and confequently the difference 
of the logarithms of its height, at both ftations, 
being the fame, as if the heat of both barometers had 
agreed with that of the fixt temperature. I fhall now 
therefore fuppofe the upper barometer is to be 
corrected, to reduce it to the temperature of the 
lower one, and that b fignifies the height of this ba- 
rometer, as obferved, and not yet corrected y the 
correction, from what has been faid above, calling D 
the difference of height of the thermometer attach- 
ed to the barometer at the two ftations, will be 
4_ according as the thermometer ftands. 
— 54 ^ & 
higheft at the lower or upper ftation ; and the 
upper barometer corrected, inftead of by will be 
b 4. — — , which fubftituted in the formula, gives 
— 54 ^ 
log. B - log. (4^X1 + ^4 But the cor- 
reCtion, on account of the difference of heat of the 
barometer at the two ftations, may be reduced to 
a ftill eafier expreffion, in which the variable 
quantity b } the height of the /upper barometer, 
fhall 
