[ 24 o 
or contraction of the length of the column in the 
barometer; or, in other words, that the alteration, 
in the perpendicular height of the Torricellian co- 
lumn, is proportional to the change of the folid 
content of fpace, occupied by a given quantity of 
the fluid. Thofe who recoiled: the experiments of 
the celebrated boerhaave, for meafuring this 
change of volume, cannot but be ftruck with the 
great and Angular difagreement between his conclu- 
sions and thofe of M. de luc. boerhaave 
makes the whole expanfion, produced by a change of 
temperature from the o of Fahrenheit, (or the forced 
congelation of fal ammoniac ) to the heat of boiling 
water, of the whole volume, which is very 
52H 3 
little more than M. de luc found to be produced 
by a change from 3 2° of Fahrenheit (or the diflb- 
lution of natural froft) to the heat of boiling water 
(n) Vid. Element* Chemise, vol. 1. p. 174. In this place, 
the author exprefsly treats of the expanfion of quickfilvtr by 
heat; and the proportion, which he here afligns, hath been 
adopted by the writers of elementary phyflcs. But, p. 165, 
having defcribed an artificial cold, in which the thermometer 
had been funk to — 40 of Fahrenheit, he fays, “ Novimus hoc 
“ ar genii vivl corpus ab illo gradu 40 infra o, ad gradum -6co quo 
incipit ebullire ccntradhtrn fuiffe per partes 640 loti us molis 
“ 10782.” And, in the explanation of one of his copper 
plates, he deferibes a thermometer in which the quickfilver, in 
the greateft natural cold, juft filled ihe bulb, which contained, 
he fays, 11520 fuch parts as the tube contained 96. It feems 
probable, that the number 11124, which is given, p. 174, as 
the whole volume of the quickfilver in the temperature o, (a de- 
gree of Fahrenheit being the unit) hath been deduced from the 
mean of a variety of experiments upon different inftruments, 
for it differs not greatly from the mean of the two numbers 
10782 and 11520. 
i Upon 
