for events whose physical
characters are unknown. Thus the spatio-temporal measurements are
independent of the objectival physical characters. Furthermore the
character of our knowledge of a whole duration, which is essentially
derived from the significance of the part within the immediate field of
discrimination, constructs it for us as a uniform whole independent, so
far as its extension is concerned, of the unobserved characters of
remote events. Namely, there is a definite whole of nature,
simultaneously now present, whatever may be the character of its remote
events. This consideration reinforces the previous conclusion. This
conclusion leads to the assertion of the essential uniformity of the
momentary spaces of the various time-systems, and thence to the
uniformity of the timeless spaces of which there is one to each
time-system.

The analysis of the general character of observed nature set forth above
affords explanations of various fundamental observational facts:
({alpha}) It explains the differentiation of the one quality of
extension into time and space. ({beta}) It gives a meaning to the
observed facts of geometrical and temporal position, of geometrical and
temporal order, and of geometrical straightness and planeness. ({gamma})
It selects one definite system of congruence embracing both space and
time, and thus explains the concordance as to measurement which is in
practice attained. ({delta}) It explains (consistently with the theory
of relativity) the observed phenomena of rotation, _e.g._ Foucault's
pendulum, the equatorial bulge of the earth, the fixed senses of
rotation of cyclones and anticyclones, and the gyro-compass. It does
this by its admission of definite stratifications of nature which are
disclosed by the very character of our knowledge of it. ({epsilon}) Its
explanations of motion are more fundamental than those expressed in
({delta}); for it explains what is meant by motion itself. The observed
motion of an extended object is the relation of its various situations
to the stratification of nature expressed by the time-system fundamental
to the observation. This motion expresses a real relation of the object
to the rest of nature. The quantitative expression of this relation will
vary according to the time-system selected for its expression.

This theory accords no peculiar character to light beyond that accorded
to other physical phenomena such as sound. There is no ground for such a
dif