The fourth dimension

266 THE FOURTH DIMENSION

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Interior Sanat Interior Satat Ii: SYies:

We can now name any section. Take e.g. the line in the first cube from senin to senel, we should call the line running from senin to senel, senin senat senel, a line light yellow in colour with null points.

Here senat is the name for all of the line except its ends. Using “senat ” in this way does not mean that the line is the whole of senat, but what there is of it is senat. It is a part of the senat region. Thus also the triangle, which has its three vertices in senin, senel, selen, is named thus:

Area: setat. Sides: setan, senat, setet. Vertices: senin, senel, sel.

The tetrahedron section of the tesseract can be thought of as a series of plane sections in the successive sections of the tesseract shown in fig. 114, p. 191. In b, the section is the one written above. In b, the section is made by a