GRAVITATIONAL MOTION 195 



as fire and earth, which go to the extremities of straight-line motion; 

 others are such comparatively, in the sense that they are heavy or 

 light with reference to various boundaries, as air and water. But 

 there is another modality of heavy and light which is noticed in 

 the intensity of these qualities, whereby it happens that in the case 

 of two bodies, even such as tend to the same terminus, one will be 

 heavier or lighter than the other, in the sense that one will have 

 more weight than the other. And this can result from one of two 

 causes, viz., because of the aggregation of more parts of the same 

 body, as a larger portion of earth has more weight than a small 

 piece; or from the complexion and nature of the body itself, as lead 

 or gold is heavier and has more weight than earth or stone of an 

 equal size.^^ 



Thus there is in Theodoric's thought a recognition of specific 

 weights, although he gives no mathematical treatment of them, 

 and in fact is not interested in their effect on gravitational 

 motion. His position is rather that the first modality men- 

 tioned above, " according to absolute quality," is proper to 

 bodies as they are parts of the universe, and this alone deter- 

 mines the proper place or region to which a body tends, 

 whether it be element or compound. If it is a compound, it will 

 tend to a region determined by what is " predominant " in it, 

 not by " proportional parts, even an exceeding one." What 

 he means by this " predominant " is not too clear: he describes 

 it as being " according to the property and nature of the com- 

 plexion in which the species of the body is rooted, which itself 

 is one and simple." Yet the practical consequence of his view 

 is easily discerned, for he holds that " fiery bodies," i. e., 

 " shooting stars and comets," tend to the proper place of fire, 

 while " earthy bodies " such as " minerals and stones " tend 

 to the place of earth." This is clearly in accord with Aristotle's 

 doctrine in De caelo et mundo ^^ and itself adds little to the 

 latter's development. Had Theodoric been discussing the 



" Cap. 8, p. 330. 



^^ Ibid., p. 331. For the medieval understanding of the expression, "comets tend 

 to the place of fire," see Lynn Thorndike's Latin Treatises on Comets Between 1238 

 and 1S6S A.D., Chicago, 1950, passim. 



^^ Book IV, chap. 4, 311a30-b3. 



