1. Kepler , J. 1929. Neue Astronomie 34–34. München tr. M. Caspar
2. Kepler J. Neue Astronomie
München 1929 234 234 tr. M. Caspar It should be noted that the “species” is not directed towards the Sun but acts transversely to the radius-vector. Kepler illustrates the point by comparing the action of the “species” to that of the magnetic force at points on the perpendicular bisector of the axis of a magnet, where the lines of force are parallel to the axis (ibid., p. 229). To explain the variation in the radius-vector as the planet describes its elliptical orbit, Kepler supposes the Sun to be a magnet having one pole at the centre and the other spread over its surface, the latter pole attracting and repelling the planet alternately, as the two magnetic poles of the planet point in turn towards the Sun.
3. Kepler , J. 1929. Neue Astronomie 229–229. München tr. M. Caspar
4. Frisch , ed. 1858–70. Kepleri opera omnia Vol. iii, 179–179. Frankfurt