TWELFTH ANNUAL MEETING. 63 
a similar circuit, and in succession through any number of cir- 
cuits, would finally reach any defined lower level with no greater 
velocity than that attained in the first circuit described. Were 
it practicable to subject every molecule of water passing through 
a fish-way to the constrained movement above indicated, the 
result would be a descending current, the average velocity of 
which would not exceed the average velocity of a molecule in 
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