[Footnote 8: From _Harpers Magazine_ for February, 1922.]
[Footnote 9: It is interesting to note that the relativity theory leads
to the conception of a symmetrical four-dimensional world space
(Minkowski), in which in general each of the four dimensions comprises
space and time conceptions, and the segregation into three dimensions of
space and one dimension of time occurs only under special conditions of
observation. (AUTHOR.)]