[ 2 3 8 ] 
rel usance, were it not of too little importance to 
derogate, in the leaf! degree, from the general 
merit of M. de luc’s elaborate and invaluable 
work. 
The quantity of the correction in qnefcion, is thus 
determined. At times, when the barometer, in a 
temperate air, flood at 27 Paris inches, M. de luc 
tried what change was effe&ed in its height, by 
changes of temperature, induced by art in the 
quickfilver, without any alteration in the ftate of the 
atmofphere ; and, by repeated experiments of this 
kind, it was found, that the difference between the 
length of the column of quicklilver, fucceflively 
heated to the temperature of boiling water, and 
cooled to that of melting ice, amounted to half a 
Paris inch exactly ; that is, to JLth of the mean- 
height W. But the whole extent of the thermome- 
ter’s fcale, from the temperature of melting ice to M. 
de luc’s boiling point, being 178° of bird’s Fahren- 
heit, the change of the height of the barometer, due 
to i° of bird’s Fahrenheit is always — = . 
J 54. x 178 9612 
And if n denote the number of degrees of bird’s 
Fahrenheit, in the difference of the temperatures of 
the quickfilver, in the barometers, at different ffations, 
the reduction will be > that i s t0 the height 
of the warmer column muff be fhortened by this 
part of its own length, or that of the cooler aug- 
mented by the like part, to reduce either, to the 
height it would have flood at, at the time and place 
of obfervation, with the temperature of the other. 
(/) Recberch. fur les Mod if* del’Atm. §. 362 — 364. 
Thefe 
