of the common Air at Sea. 357 
After having exercifed myfelf during fome time in 
performing the experiment in a water tub much too 
fmall for the purpofe, I at laft acquired a habit of doing 
it tolerably well. I then began to make my experiments 
regularly at about eleven o’clock; and I have the pleafure 
to inform you, that I found the fea air at the place indi- 
cated of a fuperior purity to any common air I ever met 
with lince the month of June laft (when I began to en- 
gage in the courfe of experiments which have afforded 
me the materials of my work lately publifhed Upon Ve- 
getables) either in my country retirement, or in London. 
In fix different trials made one after another in the fhort 
manner defcribed in my book, p. 278. et feq. !a> I found, 
that the two meafures of air (one of common and one of 
nitrous air) occupied from 0.91 to 0.94; which differ- 
ence in the refult, though but fmall in itfelf, was owing 
to the difadvantage of not having a veffel deep enough 
to move the glafs tube in w'ith eafe, for the purpofe of 
mixing the two airs together, and to my not having yet 
acquired the habit of ufing the portable apparatus. 
I tried alfo the air of this fpot in the manner ufed by 
Abbe fontana, which I have defcribed in my book, 
(a) It cor.ftfts in letting up into the glafs tube one meafure of Common air, - 
and after this one meafure of nitrous air, and fhaking the tube forcibly in the 
Water trough juft at the moment the two airs come into contact with each other. 
B b b 2 p. 1 55. 
