indeed
important functions in guiding the flight; yet notice how surrounded
one is on all sides with pitfalls for the theorists. The forked tail
reminds you at once of a fish's; and yet, the action of the two
creatures is wholly contrary. A fish lashes himself forward with his
tail, and steers with his fins; a swallow lashes himself forward with
his fins, and steers with his tail; partly, not necessarily, because in
the most dashing of the swallows, the swift, the fork of the tail is
the least developed. And I never watch the bird for a moment without
finding myself in some fresh puzzle out of which there is no clue in
the scientific books. I want to know, for instance, how the bird turns.
What does it do with one wing, what with the other? Fancy the pace that
has to be stopped; the force of bridle-hand put out in an instant.
Fancy how the wings must bend with the strain; what need there must be
for the perfect aid and work of every feather in them. There is a
problem for you, students of mechanics,--How does a swallow turn?

You shall see, at all events, to begin with, to-day, how it gets along.

65. I say you shall see; but indeed you have often seen, and felt,--at
least with your hands, if not with your shoulders,--when you chanced to
be holding the sheet of a sail.

I have said that I never got into scrapes by blaming people wrongly;
but I often do by praising them wrongly. I never praised, without
qualification, but one scientific book in my life (that I
remember)--this of Dr. Pettigrew's on the Wing;[12] and now I must
qualify my praise considerably, discovering, when I examined the book
farther, that the good doctor had described the motion of a bird as
resembling that of a kite, without ever inquiring what, in a bird,
represented that somewhat important part of a kite, the string. You
will, however, find the book full of important observations, and
illustrated by valuable drawings. But the point in question you must
settle for yourselves, and you easily may. Some of you perhaps, knew,
in your time, better than the doctor, how a kite stopped; but I do not
doubt that a great many of you also know, now, what is much more to the
purpose, how a ship gets along. I will take the simplest, the most
natural, the most beautiful of sails,--the lateen sail of the
Mediterranean.

[12] "On the Physiology of Wings." Transactions of the Royal
Society of Edinburgh. Vol. xxvi., Part ii. I cannot sufficiently