364 D>\ INGENH0US2 on the Salubrity 
places fliould be examined at the fame time as the air 
near the trees. I was defirous of doing it, and gave or- 
ders to my fervant to gather air from different parts of 
London ; but the hurry of bufinefs, oceafioned by our 
approaching departure, made him forget or overlook my 
orders; and for the fame reafon I myfelf forgot to per- 
form the talk. After all, the beft, and perhaps only good 
way to clear up this matter would be, if feveral philofo- 
phers, each provided with art exactly ftmilar apparatus, and 
living in different parts of the town, and in different parts 
of the country, fhould at the fame time put the air of 
the place of their abode to the teft, and afterwards com- 
pare their notes. I conceived fome flattering hopes be- 
fore I fet out from London, that ere long fuch eu- 
diometers, as I have defcribed in my book, will come into 
the hands of many good philofophers who will take upon 
them with pleafure to perform this talk, as I heard that 
fome of them were already ordered to be made for many 
perfons, among the reft for Dr, heberden. 
Though I have fome feafon to believe, that the vici- 
nity of the trees did really contribute fomewhat to ren- 
der the air purer at the above mentioned place ; yet I 
believe alfo, that the frofty weather of itfelf contributes 
to purify the atmofphere (perhaps by checking a great 
many 
