extracted from different Kinds of Waters . 447 
When all the errors are corrected it will he found, 
that the difference between the air of one country and 
that of another, at different times, is much lefs than what 
is commonly believed, and that the great differences 
found by various obfervers are owing to the fallacious 
effects of uncertain methods. This I advance from ex- 
perience; for when I was in the fame error, I found very 
great differences between the refults of the experiments 
of this nature which ought to have been limilar ; which 
diverfities I attributed to myfelf rather than to the me- 
thod I then ufed. At Paris I examined the air of dif- 
ferent places at the fame time, and efpecially of thofe 
fituations where it was moft probable to meet with in- 
fected air, becaufe thofe places abounded with putrid 
fubftances and impure exhalations ; but the differences I 
obferved were very fmall, and much lefs than what could 
have been fufpeCted, for they hardly arrived to one fif- 
tieth of the air in the tube. Having taken the air of the 
hill called Mont Valerien at the height of about 500 
feet above the level of Paris, and compared it with the 
air of Paris taken at the fame time and treated alike; I 
found the former to be hardly one thirtieth better than 
the latter. In London I have obferved almofl the fame. 
The air of Iflington and that of Lori'don fuffered an 
equal diminution by the mixture of nitrous air; yet the 
N n n 2 
air 
