[ 215 j 



very fmall degrees of difference in the goodnefs 

 of air. I have not attended much to this circum- 

 stance, having ufed this teft chiefly for greater 

 differences ; hut, if I did not deceive myielf, I 

 have perceived a real difference in the air of my 

 f}:udy, after a few perfons have been with me in, 

 it, and the air on the outride of the houie. Alio 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- 

 nifhed fo much by an equal mixture of nitrous ahv 

 every other circumftance being as nearly the fame 

 as I could contrive. It may perhaps be poffible, 

 but I have not yet attempted it, to diftinguifh 

 fome of the. different winds, or the air of different : 

 times of the year, by this teft. 



By means of this teft I was able to determine 

 what 1 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 

 reipecT-to refpiration ; and yet if 'nitrous air may 

 be depended upon for furniihing an accurate teft, it 

 muff be rather -more than one third worfe than. 

 common air, and have' = been diminifhed by the 

 fame general. Caufe of the other diminutions of air. 

 For when, after many trials, I put one.^ mealure 

 of thoroughly putrid and highly noxious air, into 

 the fame veflel with two mealures of good whole- 

 fome air, and into another veflel an equal quan- 

 tity, vi%. three mealures 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- 

 muiifhed rather more than the latter... h agrees 



with 



