(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, {474} 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.