GRAVITATIONAL MOTION 201 



in nature and attributes their composite aspect to two com- 

 ponent principles, one being the gravity or levity of the 

 predominant elements of which the bodies are composed, 

 accounting for the straight-line component of their motion to 

 or from some center of gravity, the other being a natural form 

 added to the gravitational principle by a generating force, and 

 accounting for the non-linear component of their motion. This 

 suggestion is pregnant with consequences if it could be under- 

 stood as applying to the case of the heavenly bodies, and the 

 question naturally arises if Theodoric, writing at the latest 

 in the first decade of the fourteenth century, could have 

 anticipated this seventeenth-century development of celestial 

 mechanics. 



The answer is to be found in another unedited opusculum of 

 Theodoric entitled De intelligenciis et motor ibus celorum.^^ 

 Here he introduces the notion of composite motions once again, 

 and precisely in the context where one might expect him to do 

 so, namely, in connection with the astronomical theories of 

 eccentrics and epicycles. Theodoric specifically rejects Aver- 

 roes' adherence to the literal text of Aristotle, maintaining that 

 Aristotle need not be understood as meaning that heavenly 

 bodies must revolve in circular orbits exactly concentric with 

 the midpoint of the universe, as Averroes interprets him, and 

 suggesting that " perhaps he [Aristotle] wished ' center ' to be 

 understood more generally, for the natural center of any natural 

 circle whatsoever," as opposed to the center of the world. "^ 

 His reason for urging a different interpretation of the Aris- 

 totelian text is based on " the efficacy of the demonstrations " 

 in Ptolemy's Ahnagest; here, as in other places, Theodoric is 

 more convinced by the observational evidence " of the astrol- 

 ogers " than he is by the authority of Aristotle.^" Granting the 



^® This opusculum was probably written in the first decade of the fourteenth 

 century. There are two manuscript copies extant: Cod. Vat. Lat. 2183, henceforth 

 referred to as U; and Cod. Vindobon. (Dominikanerkloster) 138/108. Where 

 readings of the Latin text are given below, they are based on U. 



"* Cap. 11, U o8va: Fortassis generalius voluit intelligi medium, videlicet, quod- 

 cumque medium naturale cuiuscumque circuli naturalis. . . . 



^° Capp. 11 et 14; De elementis, cap. 9 — cf. Scientific Methodology, p. 126. 



