in the Mines of the Hartz. 493 
and that if, for example, the higher barometer were 
moved horizontally as far as the column which refts 
upon the ftation of the lower one, it would not Hand at 
the fame point as when it was on the mountain ; which, 
however, is fuppofed in the formula. 
The other circumftance refpects the homogeneity of 
the air. In the open air a thoufand lateral caufes may 
introduce into the portion of the column which we mea- 
fare fome layers of air different from thofe of the two 
. ' ( . 
extremities, were it only in point of heat. And in that 
reipect the correfpondent obfervations neareft the foot of 
the mountain are not always the moil certain, becaufe 
•of the reflexions of the fun, and even of the winds 
which carry the vapours ; and the refult mull be that we 
very often find the heights too final!. I fliall not flop to 
prove 
ntse par exemple, ft le barometre fuperieur etoit avance horizontalement jufqo’a 
lacolonne qui pefe fur la ftation inferieure, il ne fe tint pas au meme point que 
fur la montagne; ce qui neantmoins eft fuppofe par la formule. 
L’autre circonftance regarde Phomogeneite de Pair. En plein air, mi lie 
caufes laterales peuvent introduire dans la portion de colonne qu’on mefure, des 
couches d’air difterentes de celles des deux extremites* ne fut-ce que differem- 
ment cliaudes. Et a cet egard ies obfervations correfpondentes les plus pres da 
pied des montagnes ne font pas toujours les plus fures a caufe des reflexions du 
Soleil, et de celles des vents qui charient les vapeurs: et il doit en refulter tres 
fouvent qu’on trouve lea hauteurs trop petites. Je ne ru’arreterai pas a le mon- 
Yql. LXIX, T t t trer. 
