Schubert, Hermann, 1848-1911 · Chicago : Open Court Pub. Co. ; London : Kegan Paul, Trench, Truebner · leaf 105
first discuss the ques- tion of the real existence of a four-dimensional space, not deciding the question whether this space, if it really does exist, is inhabited by reasonable beings who consciously act upon the world in which we exist. Among the reasons which are put forward to prove the exist-… … Fig. 38. their sides and angles congruent, but which cannot be made to co- incide by simple displacement within the plane; but we saw that this coincidence could be effected by holding fast one side of one triangle and moving it out of its plane until it had been so far turned round that it fell…
