 Finally, it should be mentioned that a similar significance is assigned to experience and empirical data in Kepler’s harmonic-musical and astrological theories, two fields which are subordinated to his greater cosmological project of HM. For astrology, he uses meteorological data, which he recorded for many years, as confirmation material. This material shows that the Earth, as a whole living being, reacts to the aspects which occur regularly in the heavens (see Boner 2013, pp. 69–99). In his musical theory Kepler was a modern thinker, especially because of the role he gave to experience. As has been noted (Walker, 1978, p. 48), Kepler made acoustic experiments with a monochord long before he wrote his HM. In a letter to Herwart von Hohenburg (KGW 15, ep. 424, p. 450), he describes how he checked the sound of a string at different lengths, establishing in which cases the ear judges the sound to be pleasurable. Kepler does not accept that this limitation is founded on arithmetical speculations, even if this was already assumed by Plato, whom he often follows, and by the Pythagoreans. On the basis of his experiments, Kepler found that there are other divisions of the string that the ear perceives as consonant, i.e., thirds and sixths.