ts which the writer has
observed. For instance, there is at first sight no reason why a cubic
foot of water should weigh 62.4 pounds. It simply does and that is all
there is to it; it does, because it does. But if he reads that a cubic
foot of water at one point on the earth's surface weighs less than it
does at another point, or that in the Northern Hemisphere the wind in a
storm revolves around the storm center in a direction contrary to the
motion of the hands of a clock, he should perceive that these facts, if
true, have a reason for them, and he should endeavor to perceive that
reason.

It must be observed at this point that, strictly speaking, there must
be a reason for any truth, even for what we may term mere facts,
excepting those which are mere definitions. There is some reason,
lying in the constitution and arrangement of its atoms, why a cubic
foot of water at a given {12} spot and at a given temperature weighs
62.4 pounds. But there is no reason why New York is 90 miles from
Philadelphia; those two points 90 miles apart are simply so named or
defined. Many truths which are accepted as mere facts, the explanation
being unknown, in the course of time are explained by the progress of
science. Thus, for many years the fact that a magnetic needle pointed
toward the North was a mere unexplained fact, but later the reason was
discovered. The same is true of the fact that the pollution of
drinking water by sewage may cause typhoid fever. The point is that
the student must continually discriminate, continually inquire, and, as
he reads, keep a list of points, the reason for which he cannot then
discover, but which he perceives must have a discoverable reason. He
should not go too deeply into this, but should preserve his sense of
proportion; for if he follows every possible line of inquiry back to
its source he will progress but slowly. Thus, if he is studying
descriptive astronomy and reads that the sun is ninety-two million
miles from the earth, or that Jupiter has nine moons, or that the star
Sirius is moving away from the earth with a velocity of eleven miles
per second, or that the moon always turns the same half toward the {13}
earth, he should perceive that he cannot at that stage try to get back
of these facts, but he may well make a note of them as questions to be
later examined, if not as to the cause, at least as to how the fact is
ascertained.

It does not follow that he should never leave t