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The screw of a steamer acts also in a similar way, and 
perhaps this is the most perfect machine for the purpose of 
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propulsion that can be invented. But as rapid rotatory motion 
is requisite to drive the screw with effect, the machinery is not 
of the simplest kind. 
A method of propelling has been tried, where motion is 
obtained by driving water through a tube astern. This, how- 
ever, is but another form of the screw. 
Another method has been proposed where the action of the 
foot of a water-fowl is imitated. 
The present method is one founded on an attempt at a 
closer imitation of the action of a fish’s tail. 
The following is the result of some experiments made about 
two years ago on a lake in Wales. Two wooden pipes about 
26 feet long were covered with canvas and tarred: they were 
fixed parallel about 1 yard apart, and a seat raised above them. 
