this machine we find affairs in a very different state. During his
climbing he has been doing a vast amount of other work, both internal
and external. His arms, his whole muscular system, in fact, has been
vigorously at work, all drawing upon his total available energy. His
brain has been in constant and unremitted action, as well as the other
internal organs, which require a greater proportional amount of energy
than they did in the bird. Besides this, he has been radiating his
animal heat into space in a far greater amount. All these parts must
be supplied; they cannot be neglected while the accumulated surplus is
given to the machinery for locomotion or lifting. This then is what
constitutes what I call the difference in the machine, which is purely
one of organic development depending upon the functions nature has
determined that the different organs shall perform. As for the
pterodactyl quoted in the last article, I have only to remark that
this discussion arose purely from a consideration of what was the best
type of flying apparatus nature had given man to study, and I claim
that this prehistoric bird of geology does not come within this class.
For if it is not fully established that this species had become
extinct long before the appearance of man on the globe, it is at least
certain that the man of that early day had not dreamt of flying and
was presumably content if he could find other means to evade the
pterodactyl's claw.

F.J.P., U.S. Army.

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