204 W. A. WALLACE 



he undertakes to do in the opusculum De elementis, where he 

 works out an explanation that is rather ingenious, even though 

 quite implausible from the viewpoint of modern science. The 

 motion of the tides, for Theodoric, is yet another case where 

 " universal nature " provides for the needs of the universe by 

 a composite motion, and this by inducing a motive principle 

 that comes " effectively " from the heavenly bodies (particu- 

 larly the moon) , and " passively " from sea water as being 

 naturally adapted to receive this influx/^ The mode of trans- 

 mission of the force deriving from the heavenly bodies is based 

 on an interpretation of Proclus,^* whereby Theodoric conceives 

 of some generic influence, originating with the separated sub- 

 stances, as being more and more determined and composed as 

 it works down through the heavenly spheres, finally receiving 

 its ultimate determination from the moon.^^ Theodoric does 

 not regard this influence as an attraction which exerts a pull 

 on the sea, but rather conceives it as somehow effecting an 

 alteration within the sea water, which makes it expand and 

 thus extend its boundaries on land, thereby accounting for the 

 rise (and fall) of the tides. 



Interestingly enough, Theodoric proposes a mechanistic type 

 of explanation for this motion which is not without empirical 

 foundation. As far as he can discern, tidal motions are 

 restricted to bodies of sea water, and are not found in fresh 

 water.^" Thus he proposes that sea water can be regarded as 



^^ Cap. 22, M 15vb, U 143ra-b. 



^* Cap. 23, M 16ra, U 143rb-va: Sicut dicit Proclus, 135 proposicione et 136 

 proposicione, dicit quod omnes illarum substanciarum separatarum potencie de- 

 sursum inchoantes, et per proprias medietates procedentes usque ad extrema, 

 perveniunt et ad loca circa terrain. . . . Sicut dicit Proclus 54 proposicione, sic: 

 omne quod a secundis producitur, et a prioribus et a causalibus producitur eminen- 

 cius. — The references are to the Elementatio theologica. Cf. Proclus, The Elements 

 of Theology, A Revised Text with Translation, Introduction and Commentary, by 

 E. R. Dodds (Oxford: Univ. Press, 1933), Props. 135-6, pp. 120-121, and Prop. 56 

 (cited as Prop. 54 by Theodoric), pp. 54-55. 



*^ Cap. 23, M 16ra, U 143rb. 



^* Cap. 24, M 16va, U 144ra: Sufficiant ilia que dicta sunt nonnulla racione, cui 

 racioni concordat hoc quod videmus in aquis dulcibus, sive sint fluentes sive sint 

 stagna, scilicet, quod non videmus ibi notabiliter eas vaporare et moveri extra 



