128 Mr . cavendish's Account of 
to the parcels of air tried on the former day being really more 
dephlogifticated than thofe tried on the latter, but only to 
fo me un perceived difference in the manner of trying the expe- 
riment ; or elfe to fome unknown difference in the nature of 
the water or nitrous air employed. A circumftance which 
teems to fhew that it was owing to the firft of thefe two caufes 
is, that it frequently happened, that on thofe days in which 
tire tefls taken in the firft method came out greater than ufual, 
thofe taken in Fontana’s manner, or in the fecond method, 
did not do fo .; the trials, however, made in thefe two methods 
were too few to determine any thing with certainty. On the 
whole there is great reafon to think, that the air was in reality 
not fenlibly more dephlogifticated on any one of the fixty days 
on which I tried it than the reft. 
The higheft teft I ever obferved was 1. 100, the loweft 1.068, 
the mean 1.082. 
I would by all means recommend it to thofe who defire to 
compare the air of different places and feafons, to fill bottles 
with the air of thofe places, and to try them at the fame time 
and place, rather than to try them at the time they were filled, 
as all the errors to which this experiment is liable, as well 
thofe which proceed from fmall differences in the manner of 
trying the experiment, as thofe which proceed from a difference 
in the nature of the water and nitrous air, will commonly be 
much lefs when the different parcels of air are tried at the 
fame time and place than at different ones ; provided only, that 
air can be kept in this manner a fufficient time without being 
injured, which I believe it may, if the bottles are pretty large, 
and care is taken that they, as well as the water ufed in filling 
them with air, are perfectly clean. I have tried air kept in the 
abovementioned manner for upwards of three-quarters of a 
year 
