494 Afr. DE LUC on Barometrical Meafures 
prove ft. In mines, on the contrary, the air being in- 
clofed as in a canal, where it is always in motion, it con- 
tinually intermixes and becomes more homogeneous : it 
contracts there a temperature which is more uniform or 
more gradually different, fo that we can more certainly 
fix the mean flate of it. 
On thefe two accounts, therefore, barometric meafures 
ought to be more regular in moft mines than on the fides 
of mountains ; becaufe the obfervations are made nearly 
at the extremities of one and the fame column, and becaufe 
the whole column is more nearly fimilar to its extremities ; 
confequently we are furerthat the particular cafe is not an 
exception to the rules. Now it has happened, that in all 
the obfervations which I have made in the Hartz mines, 
my rules, drawn from a mean among my obfervations in 
open 
Irer. Dans les mines au contraire, fair etant renferme eomme dans nn canal, 
ou il eft toujours en mouvement, fe mele fans cefte et fe rend pins homcgene.: 
furtout il y contrafte une temperature plus uniforme ou plus graduellement dif- 
ferente; enfortequ’on peut plus furement en fixer le terme moyen. 
Les mefures barometriques doivent done, par ces deux confiderations, etre 
plusregulieres dans la pi apart des mines, que fur les pentes des montagnes; e’eft 
a dire parce que les obfervations font faites a peupres aux extremites de la meme 
colonne, etque la totalite de la colonne a des rapports plus reguliers avec fes 
extremites. Ainfi l’on eft plus fur que le cas n’eft pas une exception aux regies. 
Or il fe trouve en meme terns, que dans toutes les obfervations, que j’ai faites 
dans les mines du Hartz, mes regies, tirees du milieu entre mes obfervations en 
plein 
