U4- Sir Benjamin Thompson’s Experiments 
common air ; and this agrees with the obfervations of Dr. 
Priestley, and feems to juflify his opinion with refpedt to 
the caufe of the fertility of lands wafhed by waters iffuing from 
the earth. 
If the above experiment fhews that fomething is wanted to 
be mixed with water, in order to enable it to yield pure air, 
when expofed to the aflion of the fun’s light, the following, 
fhew, that this fomething , whatever it may be, is frequently to 
be found in the water itfelf, in its natural Bate. 
Experiment N° 27. 
A large jar of clear white glafs, containing 455 cubic inches, 
being wafhed very clean, was filled with frefh fpring water, 
and inverted in a glafs bafon of the fame, and placed in the 
middle of the garden of the Elector’s Palace, where it was 
left expofed to the weather 28 days. 
At the fame time another like jar was filled with water, 
taken from a pond in the garden, in which many aquatic 
plants were growing, and was expofed in the fame place, and 
during the fame period. This water had a very faint greenifh 
caff. The pond from which it was taken is fed by a large river 
(the Ifar), which runs by the town. 
The fecond day after thefe waters had been expofed in the fun, 
I obferved, that a fmall quantity of air had collected itfelf at 
the upper part of each of the jars. 
The third, fourth, and fifth days, the pond water furnifhed 
air in pretty large quantities ; and it went on to yield it without 
intermiflion, when the fun fhone upon it, till the fourteenth 
day, when it feemed to be nearly exhaufted. I continued the 
experiment, however, till the twenty-eighth day, though during 
the 
