f 96 ] 
it is an amufing fight to obfervé 
in a jar full of pump-water the ex- 
tremity of a branch of a vine, which 
contains leaves of different ages; 
from the matureft to thofe which 
only begin to unfold themfelves. 
The air-bubbles make firft their 
appearance upon the old leaves, 
then upon thofe that follow, and 
 Jaft of all on the new-born ones. 
‘The fame proportion takes place alfo 
in the fizé of the bubbles; the 
largeft or oldeft leaves having al 
ways the largeft bubbles, and there* 
fore yielding far the greateft quan- 
tity of dephlogifticated air, 
As it feems to be almoft a con* 
ftant rule, that the leaves which 
yield the greateft quantity of aif, 
yield alfo the pureft; the famé 
rule alfo takes place in the old and 
new leaves. The young leaves 
. feem 
