6g4 PHILOSOPHICAL TRANSACTIONS. [aNNO 1780. 



with some further experiments made just before my setting out for the continent: 

 this recapitulation will make tiie nature of the experiments just mentioned, and 

 their result, much more easily understood. 



The different degrees of salubrity of the atmosphere, as I found it in general 

 in my country house at Southall Green, 10 miles from London, from June to 

 September, lay between 103 and lOQ, that is, that of the 2 measures of air, 

 viz. 1 of common and 1 of nitrous air, the remaining bulk or column occupied 

 between 103 or lOQ sub-divisions in the glass tube. I was somewhat surprized 

 when, on my return to my former lodgings in Pall-Mall Court, I found the 

 common air purer in general in October, than I used to find it in the middle of 

 summer in the country; for on the 'I'ld of October, at Q in the morning, the 

 weather being fair and frosty, I found, that one measure of common air and one 

 of nitrous air occupied 100 sub-divisions in the glass tube, or exactly one 

 measure. It gave by the Abbe Fontana's method abovementioned the following 

 result, 184, 'iOB, 304; so that the quantity of both airs destroyed in this trial 

 was exactly 1 measure and -^%. of a measure, or ]q6 sub-divisions. The same 

 day at 2 o'clock in the afternoon, it being then rainy weather, the air was some- 

 what altered for the worse; for at that time 1 measure of common and 1 of 

 nitrous air occupied 102. 



The next day, October 23, it being rainy weather, the state of the atmosphere 

 was the same in the uiorning as it was the day before in the afternoon: for 1 

 measure of common and 1 of nitrous air occupied 102; and the result of Abbe 

 Fontana's method was as follows, 1 84^, 211, 307, so that the quantity of both airs 

 destroyed amounted to 193. 



October 24, I again examined the state of the atmosphere at 9 in the morn- 

 ing, the weather being serene; I found it restored to its former goodness; for 1 

 measure of common and 1 of nitrous air occupied 100, or exactly 1 measure; 

 and the result of Abbe Fontana's method was 184, 207, 304. At 7 in the 

 evening of the same day the air was again worse; for 1 measure of common and 

 1 of nitrous air occupied 103. 



October 25, I examined the air at 1 1 in the morning, the sky being cloudy, 

 and found, that 1 measure of common and 1 of nitrous air occupied 102. I 

 put it again to the test at 1 1 at night, and found, from 5 different trials, that 

 1 measure of it with 1 of nitrous air occujiied 105. October 26, the weather 

 being very dark and rainy, I measure of common and 1 of nitrous air occupied 

 105. 



Though I have some reason to believe, that the vicinity of the trees at the 

 back of my lodgings, did really contribute somewhat to render the air purer at 

 the abovementioned place; yet I believi; also, that the frosty weather of itself 

 contributes to purify the atmosphere, jjerhaps by checking a great many causes 



