[ 2, 5 ] 
very fmall degrees of difference in the goodnefs 
of air. I have not attended mifch to this circum- 
ftance, having ufed this teft chiefly for greater 
differences ; but, if I did not deceive myfelf, I 
have perceived a real difference in the air of my 
ftudy, after a few perfons have been with me in 
it, and the air on the outfide of the houfe. Alfo a 
phial of air having been fent me, from the neigh- 
bourhood of York,, it appeared not to be fo good 
as the air near Leeds; that is, it was not dimi> 
niflied fb much by an equal mixture of nitrous air,, 
every other circumffance being as nearly the fame 
as I could contrive.. It may perhaps be poflible,, 
but I have not yet attempted it, to diftinguifh 
lbme of the different winds,, or the air, of different 
times of the year, by this teftx 
By means of this teft I was able- to determine- 
what I was before in. doubt. about, ,viz. the kind as, 
well as the degree of'injury done to air by candles- 
burning in it. I: could not tell with certainty by. 
means of mice, whether it was at all injured with 
refpeft to refpi ration.; and: yet if nitrous air may 
be depended upon for furifflhing an accurate teft, it 
muft be rather more than, one third worte than, 
common air, and have been diminifhed by the 
lame general caufe of the other diminutions of air. 
For when, after many trials,. I .put one meature ' 
of thoroughly, putrid and highly, noxious air,, into 
the fame veflei with two meafures of good whole* 
fome air, and into another veflei an equal quan- 
tity, viza three meafures of air. in which «a -Candle 
had burned out ; and then put equal quantities of 
nitrous air to each of them, the former -was di- 
tYUufthed. rather more than the- latter. It; agrees. 
with . 
