202 OPERATIONS SUBSIDIARY TO INDUCTION. 



in comparing various instances of the phenomenon, to ascertain 

 in what those instances agreed, they missed the important 

 points of agreement ; and fastened upon such as were either 

 imaginary, and not agreements at all, or if real agreements, 

 were comparatively trifling, and had no connexion with the 

 phenomenon, the law of which was sought. 



Aristotle, philosophizing on the subject of motion, remarked 

 that certain motions apparently take place spontaneously; 

 bodies fall to the ground, flame ascends, bubbles of air rise in 

 water, &c. : and these he called natural motions ; while others 

 not only never take place without external incitement, but 

 even when such incitement is applied, tend spontaneously to 

 cease ; which, to distinguish them from the former, he called 

 violent motions. Now, in comparing the so-called natural 

 motions with one another, it appeared to Aristotle that they 

 agreed in one circumstance, namely, that the body which 

 moved (or seemed to move) spontaneously, was moving 

 towards its own place; meaning thereby the place from whence 

 it originally came, or the place where a great quantity of 

 matter similar to itself was assembled. In the other class of 

 motions, as when bodies are thrown up in the air, they are, on 

 the contrary, moving from their own place. Now, this con- 

 ception of a body moving towards its own place may justly be 

 considered inappropriate ; because, though it expresses a cir- 

 cumstance really found in some of the most familiar instances 

 of motion apparently spontaneous, yet, first, there are many 

 other cases of such motion, in which that circumstance is 

 absent: the motion, for instance, of the earth and planets. 

 Secondly, even when it is present, the motion, on closer 

 examination, would often be seen not to be spontaneous : as, 

 when air rises in water, it does not rise by its own nature, but 

 is pushed up by the superior weight of the water which presses 

 upon it. Finally, there are many cases in which the sponta- 

 neous motion takes place in the contrary direction to what the 

 theory considers as the body's own place; for instance, when 

 a fog rises from a lake, or when water dries up. The agree- 

 ment, therefore, which Aristotle selected as his principle of 

 classification, did not extend to all cases of the phenomenon he 



