natural articulations. We can, we ought to, divide it as we please. All
moments count. None of them has the right to set itself up as a moment
that represents or dominates the others. And, consequently, we know a
change only when we are able to determine what it is about at any one of
its moments.

The difference is profound. In fact, in a certain aspect it is radical.
But, from the point of view from which we are regarding it, it is a
difference of degree rather than of kind. The human mind has passed from
the first kind of knowledge to the second through gradual perfecting,
simply by seeking a higher precision. There is the same relation between
these two sciences as between the noting of the phases of a movement by
the eye and the much more complete recording of these phases by
instantaneous photography. It is the same cinematographical mechanism in
both cases, but it reaches a precision in the second that it cannot have
in the first. Of the gallop of a horse our eye perceives chiefly a
characteristic, essential or rather schematic attitude, a form that
appears to radiate over a whole period and so fill up a time of gallop.
It is this attitude that sculpture has fixed on the frieze of the
Parthenon. But instantaneous photography isolates any moment; it puts
them all in the same rank, and thus the gallop of a horse spreads out
for it into as many successive attitudes as it wishes, instead of
massing itself into a single attitude, which is supposed to flash out in
a privileged moment and to illuminate a whole period.

From this original difference flow all the others. A science that
considers, one after the other, undivided periods of duration, sees
nothing but phases succeeding phases, forms replacing forms; it is
content with a _qualitative_ description of objects, which it likens to
organized beings. But when we seek to know what happens within one of
these periods, at any moment of time, we are aiming at something
entirely different. The changes which are produced from one moment to
another are no longer, by the hypothesis, changes of quality; they are
_quantitative_ variations, it may be of the phenomenon itself, it may be
of its elementary parts. We were right then to say that modern science
is distinguishable from the ancient in that it applies to magnitudes and
proposes first and foremost to measure them. The ancients did indeed try
experiments, and on the other hand Kepler tried no experiment, in the
proper s