MOVEMENT OF ANIMALS, ii.-iii. 



paint him '^ ; for they make him emit the breath 

 from his own hps. For whether one emits the 

 breath gently or so strongly as to create the greatest 

 gale (and the same is true if that which is thrown 

 or pushed is something other than breath), it is 

 necessary, first, that one should be supported upon 

 one of one's own members, which is at rest, when one 

 pushes, and secondly, that either this member itself 

 or that of which it forms part, should remain still, 

 resting upon something which is external to it. Now 

 the man who tries to push the boat while he himself 

 is in it and leaning upon it, naturally does not move 

 the boat, because it is essential that that against 

 wliich he is leaning should remain still ; but in 

 this case that which he is trying to move and that 

 against which he is leaning, is identical. If, on 

 the other hand, he pushes or drags the boat from 

 outside, he can move it ; for the ground is no part of 

 the boat. 



III. The difficulty may be raised, whether, if some- 

 thing moves the whole heaven, this motive power 

 must be unmoved and be no part of the heaven nor 

 in the heaven. For if it is moved itself and moves the 

 heaven, it can only move it by being itself in contact 

 with something that is immovable, and this can be no 

 part of that which causes the movement ; or else, if 

 that which causes the movement is from the first im- 

 movable, it will be equally no part of that which is 

 moved. And on this point at any rate they are quite 

 right who say that, when the sphere is moved in a 

 circle, no part of it whatsoever remains still ; for 

 either the whole of it must remain still, or its continu- 

 ity must be rent asunder. They are not right, how- 

 ever, in holding that the poles possess a kind of force, 



447 



