Strona 176 z 212

It is easily seen that the three-dimensional spherical space is

quite analogous to the two-dimensional spherical surface. It is

finite (i.e. of finite volume), and has no bounds.

It may be mentioned that there is yet another kind of curved

space: "elliptical space." It can be regarded as a curved space

in which the two "counter-points" are identical

(indistinguishable from each other). An elliptical universe can

thus be considered to some extent as a curved universe possessing

central symmetry.