of the common Air at Sea. 359 
before my fetting out for the continent : this recapitula- 
tion will make the nature of the experiments juft men- 
tioned, and their refult, much more eaftly underftood. 
The different degrees of falubrity of the atmofphere, 
as I found it in general in my country houfe at Southall 
Green, ten miles from London, from June to Septem- 
ber, lay between 103 and 109, that is to fay, that of the 
two meafures of air, viz. one of common and one of ni- 
trous air, the remaining bulk or column occupied be- 
tween 103 or 109 fub-divifions in the glafs tube. 
I was fomewhat furprized, when upon my return to 
town to my former lodgings in Pall Mall Court, I found 
the common air purer in general in Odlober than l ifted 
to find it in the middle of fummer in the country ; for 
on the 2 2d of October, at nine o’clock in the morning, 
the weather being fair and frofty, I found, that one mea- 
fure of common air and one of nitrous air occupied 100 
fub-divifions in the glafs tube, or exadtly one meafure. 
It gave by the Abbe fontana’s method above men- 
tioned the following refult, 184, 208, 304; fo that the 
quantity of both airs deftroyed in this trial was exactly 
one meafure and T 9 A of a meafure, or 196 fub-divifions. 
That very day, at two o’clock in the afternoon (it being 
then rainy weather) the air was fomewhat altered for the 
worfe ; 
