Outlines of the Earths History | Page 3

world by
creatures essentially like men could not be accepted, and must be
replaced by some other view which would more effectively account for
the facts. This end they attained by steps which can not well be related
here, but which led them to suppose separate powers behind each of the
natural series--powers having no relation to the qualities of mankind,
but ever acting to a definite end. Thus Plato, who represents most
clearly this advance in the interpretation of facts, imagined that each
particular kind of plant or animal had its shape inevitably determined
by something which he termed an idea, a shape-giving power which
existed before the object was created, and which would remain after it
had been destroyed, ever ready again to bring matter to the particular

form. From this stage of understanding it was but a short step to the
modern view of natural law. This last important advance was made by
the great philosopher Aristotle, who, though he died about twenty-two
hundred years ago, deserves to be accounted the first and in many ways
the greatest of the ancient men of science who were informed with the
modern spirit.
With Aristotle, as with all his intellectual successors, the operations of
Nature were conceived as to be accounted for by the action of forces
which we commonly designate as natural laws, of which perhaps the
most familiar and universal is that of gravitation, which impels all
bodies to move toward each other with a degree of intensity which is
measured by their weight and the distance by which they are separated.
For many centuries students used the term law in somewhat the same
way as the more philosophical believers in polytheism spoke of their
gods, or as Plato of the ideas which he conceived to control Nature. We
see by this instance how hard it is to get rid of old ways of thinking.
Even when the new have been adopted we very often find that
something of the ancient and discarded notions cling in our phrases.
The more advanced of our modern philosophers are clear in their mind
that all we know as to the order of Nature is that, given certain
conditions, certain consequences inevitably follow.
Although the limitations which modern men of science perceive to be
put upon their labours may seem at first sight calculated to confine our
understanding within a narrow field of things which can be seen, or in
some way distinctly proved to exist, the effect of this limitation has
been to make science what it is--a realm of things known as distinct
from things which may be imagined. All the difference between ancient
science and modern consists in the fact that in modern science inquirers
demand a businesslike method in the interpretation of Nature. Among
the Greeks the philosopher who taught explanations of any feature in
the material world which interested him was content if he could
imagine some way which would account for the facts. It is the modern
custom now to term the supposition of an explanation a working
hypothesis, and only to give it the name of theory after a very careful

search has shown that all the facts which can be gathered are in
accordance with the view. Thus when Newton made his great
suggestion concerning the law of gravitation, which was to the effect
that all bodies attracted each other in proportion to their masses, and
inversely as the square of their distance from each other, he did not rest
content, as the old Greeks would have done, with the probable truth of
the explanation, but carefully explored the movements of the planets
and satellites of the solar system to see if the facts accorded with the
hypothesis. Even the perfect correspondence which he found did not
entirely content inquirers, and in this century very important
experiments have been made which have served to show that a ball
suspended in front of a precipice will be attracted toward the steep, and
that even a mass of lead some tons in weight will attract toward itself a
small body suspended in the manner of a pendulum.
It is this incessant revision of the facts, in order to see if they accord
with the assumed rule or law, which has given modern science the
sound footing that it lacked in earlier days, and which has permitted our
learning to go on step by step in a safe way up the heights to which it
has climbed. All explanations of Nature begin with the work of the
imagination. In common phrase, they all are guesses which have at first
but little value, and only attain importance in proportion as they are
verified by long-continued criticism, which has for its object to see
whether the facts accord with the