Notwithstanding these counter-currents of speculation, which should
make the wise man speak smilingly of his wisdom, this summary
remains incomplete without a reference to the pressure of higher
space upon those adventurous minds that essay to deal with the
profound problems of the greater universe, and a statement of the
reasons for their feeling this pressure. These reasons are well
suggested by Professor B.G. Harrison, in his _Popular Astronomy_. He
says: "With the idea of a universe of finite dimensions there is the
obvious difficulty of the beyond. The truth is that a universe of
finite proportions is equally difficult to realize as one of
infinite extent. Perhaps the nearest analogy to infinity that we can
understand lies in our conception of a closed curve. It seems easier
to imagine the endless movement of a sphere in a circular path than
the case of one travelling in a straight line. Possibly this analogy
may apply in some way to fourth-dimensional space, but the manner of
its application is certainly not easy to understand. If we would
imagine that all co-ordinates of time and space were curved, and
eventually return to the same point, it might bring the ultimate
comprehension one degree nearer."


A HINT FROM ASTRONOMY

The physical evidence that our space is thus curved in higher space,
some have considered astronomy to furnish in what is called the
"negative parallax" of certain distant stars. This cannot be passed
by, though it is too deeply involved with the probable error of the
observers themselves to be considered more than an interesting fact
in this connection. Every one knows that the difference of angle
under which an object is seen from two standpoints is called its