to show themselves the most reserved, are themselves led to
forget the experimental character of the laws they have propounded,
and to see in them imperious beings whose authority, placed above all
verification, can no longer be discussed.

Others, on the contrary, carry prudence to the extent of timidity.
They desire to grievously limit the field of scientific investigation,
and they assign to science a too restricted domain. They content
themselves with representing phenomena by equations, and think that
they ought to submit to calculation magnitudes experimentally
determined, without asking themselves whether these calculations
retain a physical meaning. They are thus led to reconstruct a physics
in which there again appears the idea of quality, understood, of
course, not in the scholastic sense, since from this quality we can
argue with some precision by representing it under numerical symbols,
but still constituting an element of differentiation and of
heterogeneity.

Notwithstanding the errors they may lead to if carried to excess, both
these doctrines render, as a whole, most important service. It is no
bad thing that these contradictory tendencies should subsist, for this
variety in the conception of phenomena gives to actual science a
character of intense life and of veritable youth, capable of
impassioned efforts towards the truth. Spectators who see such moving
and varied pictures passing before them, experience the feeling that
there no longer exist systems fixed in an immobility which seems that
of death. They feel that nothing is unchangeable; that ceaseless
transformations are taking place before their eyes; and that this
continuous evolution and perpetual change are the necessary conditions
of progress.

A great number of seekers, moreover, show themselves on their own
account perfectly eclectic. They adopt, according to their needs, such
or such a manner of looking at nature, and do not hesitate to utilize
very different images when they appear to them useful and convenient.
And, without doubt, they are not wrong, since these images are only
symbols convenient for language. They allow facts to be grouped and
associated, but only present a fairly distant resemblance with the
objective reality. Hence it is not forbidden to multiply and to modify
them according to circumstances. The really essential thing is to
have, as a guide through the unknown, a map which certainly does not
claim to represent all