labours of Larmor, Lorentz, Einstein, and Minkovski
have opened a new world of thought as to the relations
of space and time to the ultimate data of perceptual
knowledge. The present work is largely concerned with
providing a physical basis for the more modern views
which have thus emerged. The whole investigation is
based on the principle that the scientific concepts of
space and time are the first outcome of the simplest
generalisations from experience, and that they are not
to be looked for at the tail end of a welter of differential
equations. This position does not mean that Einstein's
recent theory of general relativity and of gravitation is
to be rejected. The divergence is purely a question of
interpretation. Our time and space measurements may
in practice result in elaborate combinations of the
primary methods of measurement which are explained
in this work. For example, the theory of gravitational
matter may involve the theory of 'vagrant solids' which
is pointed out as a subject for investigation in article 39,
but not developed. It has certainly resulted from
Einstein's investigations that a modification of the
gravitational law, of an order of magnitude which is
v²/c² of the main effect [v being the velocity of the matter
and c that of light], will account for the more striking
outstanding difficulties otherwise unexplained by the
law of gravitation. This is a remarkable discovery for
which the utmost credit is due to the author. Now
that the fact is known, it is easy to see that it is the
sort of modification which on the simple electromagnetic
theory of relativity is likely to be required for this law.
I have however been anxious to disentangle the con-
sideration of the main positions of this enquiry from
theories designed to explain special laws of nature.

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