The fourth dimension

NOMENCLATURE AND ANALOGIES 139

null points. The yellow line will trace out a yellow and red, or orange square.

Now, turning back to fig. 78, we see that these two ways of naming, the one we started with and the one we arrived at, can be combined.

By its position in the group of four squares, in fig. 77, the null square has a relation to the yellow and to the red directions. We can speak therefore of the red line of the null square without confusion, meaning thereby the line AB, fig. 81, which runs up from the initial null point a in the figure as drawn. The yellow line of the null square is its lower horizontal line ac as it is situated in the figure.

If we wish to denote the upper yellow line sp, fig. 81, we can speak of it as the yellow r line, meaning the yellow line which is separated from the primary yellow line by the red movement,

In a similar way each of the other squares has null points, red and yellow lines. Although the yellow square is all yellow, its line cp, for instance, can be referred to as its red line.

This nomenclature can be extended.

If the eight cubes drawn, in fig. 82, are put close together, as on the right hand of the diagram, they form a cube, and in them, as thus arranged, a going up is represented by adding red to the zero, or null colour, a going away by adding yellow, a going to the right by adding white. White is used as a colour, as a pigment, which produces a colour change in the pigments with which it is mixed. From whatever cube of the lower set we start, a motion up brings us to a cube showing a change to red, thus light yellow becomes light yellow red, or light orange, which is called ochre. And going to the

Fig, 81.