have no doubt the Darwinian theory on the subject is that the feathers
of birds once stuck up all erect, like the bristles of a brush, and
have only been blown flat by continual flying.

Nay, we might even sufficiently represent the general manner of
conclusion in the Darwinian system by the statement that if you fasten
a hair-brush to a mill-wheel, with the handle forward, so as to develop
itself into a neck by moving always in the same direction, and within
continual hearing of a steam-whistle, after a certain number of
revolutions the hair-brush will fall in love with the whistle; they
will marry, lay an egg, and the produce will be a nightingale.

30. Whether, however, a hog's bristle can turn into a feather or not,
it is vital that you should know the present difference between them.

The scientific people will tell you that a feather is composed of three
parts--the down, the laminae, and the shaft.

But the common-sense method of stating the matter is that a feather is
composed of two parts, a shaft with lateral filaments. For the greater
part of the shaft's length, these filaments are strong and nearly
straight, forming, by their attachment, a finely warped sail, like that
of a wind-mill. But towards the root of the feather they suddenly
become weak, and confusedly flexible, and form the close down which
immediately protects the bird's body.

To show you the typical arrangement of these parts, I choose, as I have
said, the robin; because, both in his power of flying, and in his
color, he is a moderate and balanced bird;--not turned into nothing but
wings, like a swallow, or nothing but neck and tail, like a peacock.
And first for his flying power. There is one of the long feathers of
robin's wing, and here (Fig. 1) the analysis of its form.

31. First, in pure outline (A), seen from above, it is very nearly a
long oval, but with this peculiarity, that it has, as it were,
projecting shoulders at _a_ 1 and _a_ 2. I merely desire you to observe
this, in passing, because one usually thinks of the contour as sweeping
unbroken from the root to the point. I have not time to-day to enter on
any discussion of the reason for it, which will appear when we examine
the placing of the wing feathers for their stroke.

Now, I hope you are getting accustomed to the general method in which I
give you the analysis of all forms--leaf, or feather, or shell, or
limb. First, the plan; then the profile; then the cross-section.