beginning of recorded time, the earth, together with the other
planets and the sun, has been speeding through interstellar space at
the rate of 300,000,000 miles a year, without meeting or passing a
single star. A ray of light, travelling with a velocity so great as
to be scarcely measurable within the diameter of the earth's orbit,
takes years to reach even the nearest star, centuries to reach those
more distant. Viewed in relation to this universe of suns, our
particular sun and all its satellites--of which the earth is
one--shrinks to a point (a _physical_ point, so to speak--not
geometrical one).

The mind recoils from these immensities: let us forsake them, then,
for more familiar spaces, and consider the earth in its relation to
the sun. Our planet appears as a _moving_ point, tracing out a
_line_--a _one-space_--its path around the sun. Now let us remove
ourselves in imagination only far enough from the earth for human
beings thereon to appear as minute moving things, in the semblance,
let us say, of insects infesting an apple. It is clear that from
this point of view these beings have a freedom of movement in their
"space" (the surface of the earth), of which the larger unit is not
possessed; for while the earth itself can follow only a _line_, its
inhabitants are free to move in the two dimensions of the surface of
the earth.

Abandoning our last coign of vantage, let us descend in imagination
and mingle familiarly among men. We now perceive that these
creatures which from a distance appeared as though flat upon the
earth's surface, are in reality erect at right angles to its plane,
and that they are endowed with the power to move their members in
_three dimensions_. Indeed, man's ability to traverse the surface