[4] The words of Newton, "Hypotheses non fingo," have been often quoted
in such sort as to give an entirely incorrect idea of his real opinion
as to the relation between theoretical and practical science. As too
commonly understood, they would, in fact, make his discovery of
gravitation a great exception to his own rule. They must be taken in
connection with his definition of a hypothesis, as "whatsoever is not
deduced from phenomena." It is a part of true science, nay, it is the
highest office of the student of science to deduce theories from
phenomena. Such research stands as high above the simple observation of
phenomena as architecture stands above brick-making or stone-cutting.
But to frame hypotheses as the old Greeks did, trusting to the power of
the understanding independently of the observation of phenomena, is to
make bricks without straw and to build with them upon the sand.
[5] The point is explained in a paper called "Our Chief Timepiece Losing
Time," in the first series of my "Light Science for Leisure Hours."
[6] In the popular, but incorrect way of speaking, the balance between
the centrifugal and the centripetal force will no longer be maintained:
the increase of velocity will give the centrifugal force the advantage,
and it will slowly draw the body away from the centre. In reality there
is no centrifugal _force_, the only force acting on the earth in her
course round the sun being the sun's attraction upon her, which,
however, must keep bending her course from the straight line, if she is
to maintain her distance. In the case above imagined it would not bend
her course actively enough.
[Illustration]