“[...] The movement of the celestial bodies can be given as an example. It is not exactly circular, but elliptic; the ellipse constitutes as it were a first “specification” of the circle, by the splitting of the center into two poles or “foci” in the direction of one of the diameters which thereafter plays a special “axial” part, while at the same time all the other diameters are differentiated one from another in respect of their lengths. It may be added incidentally in this connection that, since the planets describe ellipses of which the sun occupies one of the foci, the question arises as to what the other focus corresponds to; as there is nothing corporeal actually there, there must be something belonging only to the subtle order; but that question cannot be further examined here, as it would be quite outside our subject.” SunFocusKepler S Laws Book:The Reign of Quantity & the Signs of the Times Source: The Reign of Quantity & the Signs of the Times