An introduction to mathematics, by A. N. Whitehead.

DYNAMICS 43
philosopher, should have dropped the weights
from the leaning tower of Pisa. There are
always men of thought and men of action;
mathematical physics is the product of an
age which combined in the same men impulses to thought with impulses to action.
This matter of the dropping of weights
from the tower marks picturesquely an essential step in knowledge, no less a step than
the first attainment of correct ideas on the
science of dynamics, the basal science of the
whole subject. The particular point in dispute was as to whether bodies of different
weights would fall from the same height in
the same time. According to a dictum of
Aristotle, universally followed up to that
epoch, the heavier weight would fall the
quicker. Galileo affirmed that they would
fall in the same time, and proved his point
by dropping weights from the top of the
leaning tower. The apparent exceptions to
the rule all arise when, for some reason, such
as extreme lightness or great speed, the air
resistance is important. But neglecting the
air the law is exact.
Galileo's successful experiment was not the
result of a mere lucky guess. It arose from
his correct ideas in connection with inertia
and mass. The first law of motion, as following Newton we now enunciate it, is-Every
body continues in its state of rest or of uni