- 
376 Observations on an 
rupted by this obstruction; but the action of 
the stream in the siphon will push the mass 
of air from place to place in its own direction 
until it shall be discharged at the nosle. The 
removal of this impediment will restore the 
stream to its full vigour ; upon which the 
water will begin to subside in the tub; and 
it will continue to do so, until the surface 
arrives at its proper level; unless a second 
collection of air happens to be formed in the 
mean time. We have now investigated the 
nature of the reciprocation, observable in Mr. 
Swainston’s apparatus, it proceeds entirely 
from the obstruction of air bubbles, lodged 
in the crooked canal; the formation of which 
depends on causes that act in a fortuitous or 
irregular manner ; consequently the recipro- 
cation which results from their united opera- 
tions will prove to be equally uncertain and 
variable. 
Should the preceding theory of an ebbing 
and flowing vessel receive the reader’s appro- 
bation, he will be disposed to think, that Pliny 
discovered the true nature of reciprocating 
fountains, when he compared the fluctuations 
of these springs to the interrupted and irre- 
gular stream, which issues from a bottle. In 
fact, only one circumstance seems wanting 
to render his explanation of the phenomenon 
