f. xxi j 
§* be of confiderable practical ufe; 
¢¢ and, particularly, that the air of 
“ diftant places and countries might 
“¢ be brought and examined together 
© with gréat eafe and {atisfaction; 
«but I own, that hitherto I have 
“rather been difappointed in my 
“expectation from it.” And he 
concludes thus: * I have frequently 
“taken the open air in the moft 
* expofed places in this country, at 
“ different times of the year, and in 
“ different ftates of the qweather, 
 8cC.5 ‘but never found the differ- 
ss ence fo great as the inaccuracy, 
“arifing from the method of 
fs making the trial, might eafily 
ae amount to or exceed.” - 
‘Since I faw the manner of putting 
different airs to the nitrous teft,” 
which Abbé Fontana now makes” 
ufe of, and which I have in my in- 
b3  — quities 
