4oa M. de luc’s Barometrical Obfervations on 
heights by the Barometer, that I might know whether 
in thofe pits (where exhalations of all kinds fpread them- 
felves) the condenfations of the air follow the fame laws 
that they do out of them. 
I nearly mifcarried in this interefting operation 
through an accident which had happened to my Ba- 
rometer. Having lent it to a friend, when I came to 
examine it a little before my fetting out, I found that air 
had fome how got into it. Luckily I had time enough 
to take it to pieces and make the quickiilver boil in it; a 
circumftance which I only mention in order to obferve, 
that I fucceeded fo thoroughly in this manoeuvre, that, 
from that time to this, the quickiilver has always ad- 
hered to the fummit of the tube as often as I have raifed 
it to it, juft in the fame manner as it adheres by the 
ebullition. It requires a lhake to make it defcend : and 
fometimea 
regies pour la mefure des hauteurs par le Barometre; pour favoir dans ces 
puits, ou des exhalations de tant d’efpeces fe repandent, les condenfations de 
Pair fuivroient les memes loix qu’au dehors, 
Je failiis a manquer cette intereflante operation par un accident arrive a mon 
Barometre. Je l’avois prete; et lorfque-je Pexaminai a la veille.de mon depart, 
je trouvai qu’on y avolt IaiiTe entrer de Pair. J’eus le terns heureufement de le 
demonter, et d’y faire bouillir le mercure: circonftance dont je ne fais mention, 
que pour ajouter; que je reuffis fi parfaitement dans cette operation, que des ce 
moment, pendant tout mon voyage, et jufqu’a aujourd’hui, le mercure a .tou- 
jours continue de s’attacher an fommet du tube, Iorfque je Py ramene; 
comme il s’y attache au moment de Pebullition ; et il n’en defcend que par une 
fecoulie* 
