Johannes Kepler, Harmonices Mundi [The Harmony of the World] (Linz, (Austria): Johann Planck, 1619), p. 189. From the bottom of p. 189: "Sed res est certissima extactissimaque quod proportio qua est inter binorum quorumcunque Planetarum tempora periodica, sit præcise sesquialtera proportionis mediarum distantiarum, id est Orbium ipsorum; … " (But it is absolutely certain and exact that the proportion between the periodic times of any two planets is precisely the sesquialternate proportion [i.e., the ratio of 3:2] of their mean distances, that is, of the actual spheres, … "
An English translation of Kepler's Harmonices Mundi is available as: Johannes Kepler with E.J. Aiton, A.M. Duncan, and J.V. Field, trans., The Harmony of the World (Philadelphia, Pennsylvania: American Philosophical Society, 1997); see especially p. 411.
The opening of the film Mars et Avril, by Martin Villeneuve, is based on Kepler's cosmological model in Harmonices Mundi, in which the harmony of the universe is determined by the motion of celestial bodies. Benoît Charest also composed the score according to this theory. This opening sequence can be seen here: https://vimeo.com/66697472
