Schubert, Hermann · Chicago: The Open Court publishing company; [etc., etc.] · leaf 101
ill first discuss the ques-tion of the real existence of a four-dimensional space, not decidingthe question whether this space, if it really does exist, is inhabitedby reasonable beings who consciously act upon the world in whichwe exist. Among the reasons which are put forward to prove the… … Fig. 38. their sides and angles congruent, but which cannot be made to co-incide by simple displacement within the plane; but we saw thatthis coincidence could be effected by holding fast one side of onetriangle and moving it out of its plane until it had been so far turnedround that it fell back…
