kind of trees there growing. The dreary
appearance produced by the universal brown
of the grass, was, however, nothing to that
presented by the country round here after the
great Bush fire, in the beginning of this year.
I went to the top of our Mount Swardle a day
or two afterwards, on purpose to have a look
at the scene. On every side there was nothing
but a great black plain—like a smooth pall;
the uniformity of black absorbing all the
shadows which distinguish hills and valleys to
the eye.

One unpleasant fact about this country is
the extraordinary number of malicious little
insects. First, there are the mosquitoes,
then there are countless varieties of ants—of
all sizes up to an inch in length; the largest
are, on account of their ferocity, appropriately
named "colonial bulldogs." Their bite is
severe, as I can personally testify. In addition
we have centipedes; not to forget spiders
as large as the top of a tea-cup.

In Australia there is nothing old; no old
castles or old houses. One hardly ever sees
an old man or an old woman; and I don't
think the traditions of the natives ever extend
beyond the time of their grandfathers. Even
the phrase "as old as the hills," almost loses
its point in Australia; many of them—our
Mount Swardle for instance—being extinct
volcanoes; infants, geologically, not above a
thousand years or so old.

ANIMAL MECHANICS.

WHOEVER has had the pleasure of studying
Dr. Arnott's Elements of Physics, must have
dwelt with peculiar zest on the many illustrations
of its doctrines which the author has
drawn from the structure of the human body.
Well do we remember with what a flutter of
surprise the professors and students of two
distinguished schools of medicine first learned
from Dr. Arnott's book, that atmospheric
pressure is one of the forces by which the
stability of the joints is secured; and that in
the knee joint, for instance, the articulating
surfaces of the bones are pressed together by
about sixty pounds' weight of air. For a
whole session teachers and pupils never tired
of talking about this wonderful discovery;
and endless were the experiments made on
tortured cats and dogs, as well as upon the
dead subject, to prove the truth of a proposition
which ought to have been self-evident
to men but moderately versed in natural
philosophy. It was not that those learned
professors and those earnest students had
been previously unacquainted with the
phenomenon of atmospheric pressure; they knew
as well as Dr. Arnott that every square inch
of the surface of the human body sustained
its airy burthen of fifteen pounds; they knew
as well as he, that between the articulating
surfaces of bones there was no elastic medium
interposed which could counteract that
pressure; but, unlike him, they had not learned
to put those two facts together, but had
suffered them to roll about in their minds in
unprofitable isolation, like the loose grains
in a sportsman's shot pouch. If it is a good
thing for a man to know the extent of his
own ignorance, on the other hand, it appears
to us scarcely less desirable that he should be
able to make out a true inventory of his knowledge
for the readier use thereof. "Happy
the man who knows what he knows," exclaims
the sententious Jacotot.

Dr. Arnott's work was soon followed
by an essay from the pen of the late Sir
Charles Bell, entitled "Animal Mechanics."
It is strange that the example of these
writers has hitherto incited few inquirers,
if any, to follow them upon this new field
of study. New it is, at least in modern
times; for since the extinction of what
may be called the Mechanical School of
Physiology, of which the last eminent
representative, Baglivi, died in 1706, scarcely any
anatomist had thought of comparing the facts
revealed by the scalpel with the principles of
physical statics and dynamics. Even now it
is but just beginning to be acknowledged that
the cultivators of biological and of physical
science—or, in other words, of that which
relates to living and that which relates
to dead matter—are too often content to
remain more or less ignorant, to their great
mutual detriment, each of the subjects of the
other's speculations. Hence comes defective
knowledge on both sides, now and then
clumsily pieced out with conjectures caught
up, wrong end foremost, in wild adventurous
forays across the common border. Science
suffers from this want of reciprocal commerce
between its votaries. The arts, too, are
deprived of many useful inventions, which a
more intimate knowledge of animated nature
might suggest to men of constructive
ingenuity. It is not unlikely that the inventor
of the ball and socket joint, whoever he may
have been, derived the ideas, though it were
even unconsciously, from the articulation of
the thigh bone of a quadruped, or of man with
the haunch. The celebrated shield used in
excavating the Thames Tunnel was avowedly
imitated by Mr. Brunei, from the headpiece
of a species of worm that burrows under the
silt at the bottom of rivers.

Most of the mechanical principles exhibited
in bones have been elucidated by Arnott and
Bell; but a very interesting part of the
subject has wholly escaped their notice. They
have shown, for instance, that sundry advantages
result from the hollowness of the long
bones of the limbs; that it affords not only an
ampler surface for the attachment of muscles,
but also increase of strength without increase
of weight. The strength of a cylinder of
given length and material is exactly in proportion
to its diameter, and if the mass remain
the same, the diameter can be increased only
by making the cylinder hollow. In fact, it is
only a certain thickness of the outer ring that