Mathematical philosophy, a study of fate and freedom; lectures for educated laymen, by Cassius J. Keyser.

326 MATHEMATICAL PHILOSOPHY
of length; let P be any point and, as in the figure, denote
its distances from the coordinate planes by x, y and z,
called the coordinates of P; they are also the coordinates
of the triad (x, y, z). It is plain that a P determines a
z
c x
~I~~\y
FIG. 29.
triad, and a triad a P. You see at once that ordinary
space, if regarded as a plenum of points, has three dimensions, since the points match the triads in the threedimensional system of triads of real numbers. In such