TRANSACTIONS OF THE SECTIONS. 101 



Capt. Taylor, R.N. explained, by reference to a model, his construction and ap- 

 plication of a shield to protect the paddle-wheels of steam-boats from the shock or 

 action of the sea -when riding at anchor, or sailing or scudding under canvas when 

 the steam power is not applied ; also his method of disconnecting the paddles with- 

 out stopping the engines. He also proposed to apply the steam power of vessels for 

 the purpose of working the windlass. 



On the Propulsion of Vessels by the Trapezium Paddle-ivheel and Screw, 



By G. Rennie, F.R.S. 



The author gave an 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 was the best means of propulsion with 

 which engineers were at present acquainted, and various attempts had been made 

 for its improvement. There are several objections to the square or rectangular floats, 

 particularly the shock on entering the water, and the drag against the motion of the 

 wheel on the float quitting the water ; both of which give rise to considerable vi- 

 brations. 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 di- 

 minished. 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 ; they arrive gradually at their full horizontal action, without shocks or 

 vibrations, and after their full horizontal action, quit the water without lifting it, or 

 producing any sensible commotion behind. After a great variety of experiments, he 

 found that a paddle-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 weight 

 with the ordinary rectangular floats. The Admiralty had permitted him to fit Her 

 Majesty's steam-ship African ■yvith these wheels, and he had perfect confidence in the 

 success of the experiment. Another means of propulsion was 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 adapta- 

 tion 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, was very 

 remarkable, — the latter going off much more rapidly to a point than the former. From 

 these observations hewas led to try a screw with fourwings, of a shape somewhat similar 

 to these, but bent into a conical surface, the outline being a logarithmic spiral. He 

 found also that certain portions of these might be cut off without diminishing the 

 efi"ect. With respect to ascertaining the friction of the screw on the water, great diffi- 

 culty existed ; but he would refer to his experiments, published some years ago in the 

 Philosophical Transactions, in which he measured the friction of the water against a 

 body revolving in it, by the time which a given weight took to descend; this body con- 

 sisted of rings, and he found that the friction or resistance through the water did not 

 increase in proportion to the number of rings. The results of the experiments made 

 since with the African, opposite the measured mile in Long Reach in the rit'er Thames, 

 and also with an iron steam-boat in the river Shannon, have fully realized the expec- 

 tations of the author. 



On Truscotfs Plan for Reefing Paddle- Wlieels. By W. Chatfield. 



Mr. Chatfield described, by reference to a model, an improved paddle-wheel, the 

 principal feature of which was a new application of the principle of feathering and 

 reefing. Each paddle or float is attached to an axis passing through its centre, with 

 a crank at the extremity of the axis, and the feathering is effected by the motion of a 

 roller attached to this crank, and moving in a groove eccentric to the wheels. The 

 radii of the paddle-wheel are connected at their extremities by a chain instead of a 

 rigid rim, and the reefing is effected by drawing the radii together, like the folding 



