M. Delebeuf, in a paper read before the Academie Royale de Belgique, and
published in the _Revue Scientique_, reviews the attempts of various
naturalists to make comparisons between the strength of large animals
and that of small ones, especially insects, and shows that ignorance or
forgetfulness of physical laws vitiates all their conclusions.
After a plea for the idea without which the fact is barren, M. Delbeuf
repeats certain statements with which readers of modern zoological
science are tolerably familiar, such as the following: A flea can jump
two hundred times its length; therefore a horse, were its strength
proportioned to its weight, could leap the Rocky Mountains, and a whale
could spring two hundred leagues in height. An Amazon ant walks about
eight feet per minute, but if the progress of a human Amazon were
proportioned to her larger size, she could stride over eight leagues in
an hour; and if proportioned to her greater weight, she would make the
circuit of the globe in about twelve minutes. This seems greatly to the
advantage of the insect. What weak creatures vertebrates must be, is the
impression conveyed.
But the work increases as the weight. In springing, walking, swimming,
or any other activity, the force employed has first to overcome the
weight of the body. A man can easily bound a height of two feet, and
he weighs as much as a hundred thousand grasshoppers, while a hundred
thousand grasshoppers could leap no higher than one--say a foot. This
shows that the vertebrate has the advantage. A man represents the volume
of fifteen millions of ants, yet can easily move more than three hundred
feet a minute, a comparison which gives him forty times more power, bulk
for bulk, than the ant possesses. Yet were all the conditions compared,
something like equality would probably be the result. Much of the force
of a moving man is lost from the inequalities of the way. His body,
supported on two points only when at rest, oscillates like a pendulum
from one to the other as he moves. The ant crawls close to the ground,
and has only a small part of the body unsupported at once. This
economizes force at each step, but on the other hand multiplies the
number of steps so greatly, since the smallest irregularity of the
surface is a hill to a crawling creature, that the total loss of force
is perhaps greater, since it has to slightly raise its body a thousand
times or so to clear a space spanned by a man's one step.
By what peculiarity of our minds do we seem to expect the speed of an
animal to be in proportion to its size? We do not expect a caravan to
move faster than a single horseman, nor an eight hundred pound shot to
move twelve thousand eight hundred times farther than an ounce ball.
Devout writers speak of a wise provision of Nature. "If," say they, "the
speed of a mouse were as much less than that of a horse as its body is
smaller, it would take two steps per second, and be caught at once."
Would not Nature have done better for the mouse had she suppressed the
cat? Is it not a fact that small animals often owe their escape to their
want of swiftness, which enables them to change their direction readily?
A man can easily overtake a mouse in a straight run, but the ready
change of direction baffles him.
M. Plateau has experimented on the strength of insects, and the facts
are unassailable. He has harnessed carabi, necrophori, June-beetles
(Melolontha), and other insects in such a way that, with a delicate
balance, he can measure their powers of draught. He announces the result
that the smallest insects are the strongest proportioned to their size,
but that all are enormously strong when compared bulk, for bulk, with
vertebrates. A horse can scarcely lift two-thirds of its own weight,
while one small species of June-beetle can lift sixty-six times its
weight; forty thousand such June-beetles could lift as much as a
draught-horse. Were our strength in proportion to this, we could play
with weights equal to ten times that of a horse.
This seems, again, great kindness in Nature to the smaller animal. But
all these calculations leave out the elementary mechanical law: "What
is gained in power is lost in time." The elevation of a ton to a given
height represents an expenditure of an equal amount of force, whether
the labor is performed by flea, man, or horse. Time supplies lack of
strength. We can move as much as a horse by taking more time, and can
choose two methods--either to divide the load or use a lever or a
pulley. If a horse moves half its own weight three feet in a second,
while a June-beetle needs a hundred seconds to convey fifty times
its weight an equal distance, the two animals perform equal work
proportioned to their weights. True, the cockchafer can hold fourteen
times its weight in equilibrium (one small June-beetle sixty-six times),
while a horse cannot balance nearly his own weight. But this does not
measure the amount of oscillatory motion induced by the respective
pulls. For this, both should operate against a spring.
A small beetle can escape from under a piece of cardboard a hundred
times its weight. Pushing its head under the edge and using it as a
lever, it straightens itself on its legs and moves the board just a
little, but enough to escape. Of course, we know a horse would be
powerless to escape from a load a hundred times its own weight. His head
cannot be made into a lever. Give him a lever that will make the time he
takes equal to that taken by the insect, and he will throw off the load
at a touch. The fact is that in small creatures the lack of muscular
energy is replaced by time.
Of two muscles equal in bulk and energy the shortest moves most weight.
If a muscular fiber ten inches in length can move a given weight five
inches, ten fibers one inch long will move ten times that weight a
distance of half an inch. Thus smaller muscles have an absolutely
slower motion, but move a greater proportional weight than larger.
The experimenter before mentioned was surprised to find that two
grasshoppers, one of which was three times the bulk of the other,
leaped an equal height. This was what might be expected of two animals
similarly constructed. The spring was proportioned to the bulk. In
experiments on the insects with powerful wings, such as bees, flies,
dragon-flies, etc., it was found that the weight they could bear without
being forced to descend was in most cases equal to their own. In some
cases it was more, but the inequality of rate of flight, had it been
taken into the reckoning, would have accounted for this.
Take two creatures of different bulk but built upon exactly the same
plan and proportions, say a Brobdingnagian and a Lilliputian, and let
both show their powers in the arena. Suppose the first to weigh a
million times more than the second. If the giant could raise to his
shoulder, some thirty-five feet from the ground, a weight twenty
thousand pounds, the dwarf can raise to his shoulder, not, as might be
thought, a fiftieth of a pound, but two full pounds. The distance raised
would be a hundred times less. In a race the Lilliputian, with a hundred
skips a second, will travel an equal distance with the giant, who would
take but a skip in a second. The leg of the latter weighs a million
times the most, but has only ten thousand times as many muscle fibers,
each a hundred times longer than those of the dwarf, who thus takes one
hundred skips while the giant takes one. The same physical laws apply to
all muscles, so that, when all the factors are considered, muscles of
the same quality have equal power.--_Am. Field._.
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