198 W. A. WALLACE 



components, one impressed on it by adjoining parts, another 

 arising intrinsically within the part itself. Other composite 

 motions are those of clouds, vapors and winds, when these are 

 considered as integi-al wholes apart from any internal move- 

 ments that might characterize their parts; such motions he 

 analyzes as deriving partly from the intrinsic elements of which 

 such wholes are composed, and partly from the forces that 

 generate them, which he sees as endowing them with added 

 dispositions to fulfill special purposes intended by nature. Still 

 other motions, such as those of rivers and whirlwinds, are com- 

 posite because of the reaction of the fluid with its boundaries 

 or because of the interaction that results when two natural 

 motions converge from different directions. In practically all 

 of these cases, as we shall see, the natural motion which is 

 attributed by Theodoric to the elemental constituents of the 

 fluid is a simple, straight-line motion towards the center of 

 gravity, while the component that makes the total motion 

 composite derives from an outside source and does not come 

 directly from the fluid's intrinsic components. 



The case of the complex movement of parts of a fluid medium 

 is not particularly noteworthy, except for the fact that Theo- 

 doric there uses notions associated with Averroes' solution to 

 the projectile problem,-" which may be indicative of his own 

 ideas concerning impetus. Theodoric does not commit himself 

 to any particular theory of impetus — in fact he explicitly 

 refrains from discussing this matter " — but he does speak of 

 the influence of the parts of a fluid on each other by which they 

 continue to be in motion after the source of their initial dis- 

 turbance has ceased." Since the cases of fluid and projectile 



^°Cf. Commentarium in VIII Physicorum (ed. Venetiis, 1550), Tom. IV, 195va- 

 196ra. 



"For the Latin text, see Maier, Studien V, p. 290, fn. 1. 



Cap. 13, M 15rb, U 142rb: Tale enim corpus, cum receperit motum in aliqua 

 suarum parcium, huiusmodi pars movet aliam vel alias, et sic deinceps, quod absque 

 aliquali subinteraccione parcium ad partes fieri non potest, propter talium corporum 

 spiritualitatem, ut dicit Commentator super octavum Physicorum. Partes autem sic 

 mote et propulse, alias secum trahunt propter continuitatem. Cum autem per 

 talem niocionem partes sursum vel alias extra locum suum actu fuerint, quasi per 



