Proceedings of the British “a_i ws 
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 off 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 fpats 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 asa wheel of double 
the width and weight 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 toa point much more rapidly than the former. | From 
these observations he was led to try a screw with four wings of 
@ Shape somewhat similar to these, i bent into a conical sur- 
Vol. xxi, No. 2.—Jan.-March, 1842. 
