Proteedwgs of the British Association. 337 



account of the various experiments to which he had been led, 

 on the propulsion of vessels by various forms of paddle-floats and 

 by the screw. It was generally admitted that the paddle-wheel 

 is the best means of propulsion with which engineers are at 

 present acquainted, and various attempts have been made for its 

 improvement. There are several objections to the square or rec- 

 tangular floats, particularly the shock on entering the water, and 

 the drag against the motion of the wheel on the float's quitting 

 the water ; both of which gave rise to considerable vibrations. 

 He had been led, in considering the improvement of the paddle- 

 wheel, to have recourse to nature ; and the form of the foot of 

 the duck had particularly attracted his attention. The web of 

 the duck's foot is shaped so that each part has a relation to the 

 space through which it has to move, that is, to the distance from 

 the centre of motion of the animal's leg. Hence he was led to 

 cut ofi" the angles of the rectangular floats ; and he found that 

 the resistance to the wheel through the water was not diminish- 

 ed. Pursuing these observations and experiments, he was led to 

 adopt a float of a trapezium or diamond shape, with its most 

 pointed end downwards. These floats enter the water with their 

 points downwards, and quit it with their points upwards, and 

 then arrive gradually at their full horizontal action, without shocks 

 or vibrations, and after their full horizontal action, quit the wa- 

 ter without lifting it or producing any sensible commotion be- 

 hind. After a great variety of experiments, he found that a pad- 

 dle-wheel of one half the width and weight, and with trapezium 

 floats, was as effective in propelling a vessel as a wheel of double 

 the width and v/eight with the ordinary rectangular floats. The 

 Admiralty had permitted him to fit Her Majesty's steam-ship Af- 

 rican with these wheels, and he had perfect confidence in the 

 success of the experiment. Another means of propulsion is the 

 screw, which had been applied with success by Mr. Smith in the 

 Archimedes. In examining the wings of birds and the tails of 

 swift fish, he had been particularly struck with the adaptation of 

 shape to the speed of the animals. The contrast between the 

 shape of the tail of the codfish — a slow moving fish, and the tail 

 of the mackerel — a rapid fish, is very remarkable ; the latter go- 

 ing off to a point much more rapidly than the former. From 

 these observations he was led to try a screw with four wings of 

 a shape somewhat similar to these, but bent into a conical sur- 



Vol. XLir, No. 2.— Jan .-March, 1842. 43 



