in the Mines of the Hartz. 499 
periments which prove it, we can attribute to thefe dif- 
ferences only thofe of the refults of the refearches of 
1'ome philofophers concerning the dilatations of the air 
by heat, applied to various phyfical ufes. 
In a paper lately read at the Royal Society, on the fub- 
j.e£t of refractions, I analyfed and compared different for- 
mulae of this kind, given by philofophers on whom we 
can depend. The refult of that examination was that, 
fuppofing the volume of air = 1000 when the Englifh 
thermometer of Fahrenheit is at 32 0 , if the heat of 
the air be increafed 22,8 degrees of this thermometer, its 
volume will be,, 
According 
particulieres, qui Ie prouvent, on ne peut attribuer qu’a ces differences, celies 
des refultats des recherches de divers phyficiens fur les dilatations de Fair par far 
chaleur, appliquees a divers ufages phyftques. 
C’eft a l’occafion des refractions, que, dans un memoire lu ily a pen de terns 
a la Societe Roy ale, j’ai analyfe et compare diffe rentes formules de cette efpece, 
donnees par des phyficiens, fur qui l’on peut compter. II eft refulte de cet exa- 
men, qu’en fuppofant le volume de Fair — 1000 lorfque le thermometre Anglois 
de Fahrenheit eft a 32 0 , ft la chaleur de Fair augmente de 22,8 degres de ce 
thermometre, fon volume fera: 
Sul v ant- 
