Any desired number of dimensions can be worked out mathematically but with increasing difficulty because of the impracticability of diagrammatical representation. We can generalize the idea by speaking of a “geometry of _n_ dimensions” where _n_ may stand for any number whatever from zero to infinity. A line of a given length contains an infinite number of points. A square of a given size contains an infinite number of lines. A cube of a given size contains an infinite number of plane squares. A tesseract (four-dimensional cuboid) of a given size contains an infinite number of solid cubes. And what would there be left of space if you took everything out of it, and what would become of time if nothing ever happened? In other words are not space and time merely forms of thought, the framework of ideas, and if so cannot we fix them over to suit our need of new conceptions? As a matter of fact we do. We have constructed by the aid of Euclid and his successors a geometry of three dimensions that works perfectly for all ordinary requirements and if we need a fourth dimension to accommodate these new astronomical and physical phenomena we will build on the necessary addition to our conception of space. There was no use having a fourth dimension so long as we had nothing to put in it. For ordinary earth measurements (geometry) such as laying out a town lot we only use two dimensions, length and breadth. We speak of “flat ground” and “water-level” regardless of the fact that all our “straight” lines on the earth’s surface are really curves that come back to us after going 25,000 miles or less. It is only when measuring mile lengths that we have to correct for the curvature of the earth in the third dimension. So if, as seems probable, we shall have to make allowance in astronomical measurements for the curvature of the universe in a fourth dimension it will merely mean a little labor to the astronomers and it will relieve their minds of some of their perplexities. There is nothing more mystical or mysterious or “psychical” about a fourth dimension than about the other three. A dimension is simply a measurable direction and we can use five dimensions or _n_ dimensions if we need to.