THE SCREW PROPELLER.

(Vol. ix., p. 394.)

Anon. is clearly mistaken in thinking that, when Darwin says that "the undulating motion of the tail of fishes might be applied behind a boat with greater effect than common oars," he had any idea of a screw propeller. He meant not a rotatory, but, as he says, an "undulating" motion, like that of the fish's tail: such as we see every day employed by the boys in all our rivers and harbours, called sculling—that is, driving a boat forward by the rapid lateral right and left impulsion of a single oar, worked from the stern of the boat. It was the application of steam to some such machinery as this that Darwin seems to have meant; and not to the special action of a revolving cut-water screw.

I avail myself of this occasion to record, that about the date of Darwin's publication, or very soon after, the very ingenious Earl Stanhope not only thought of, but actually employed, the identical screw propeller now in use in a vessel which he had fitted up for the purpose; and in which, by his invitation, I, and several other gentlemen, accompanied him in various trips backwards and forwards between Blackfriars and Westminster bridges. The instrument was a long iron axle,

working on the stern port of the vessel, having at the end in the water a wheel of inclined planes, exactly like the flyer of a smoke-jack; while, inboard, the axle was turned by a crank worked by the men. The velocity attained was, I think, said to be four miles an hour. I am sorry that I am not able to specify the exact date of this experiment, but it must have been between 1802 and 1805. What Lord Stanhope said about employing steam to work his machine, I do not clearly recollect. He entered into a great many details about it, but I remember nothing distinctly but the machine itself.