S*CT. XIV. 2. PRODUCTION OF IDEAS. 117 



this fpirit of animation has alfo the fame figure as 

 the medulla above defcribed. I appeal to com- 

 mon fenfe ! the fpirit of animation acts, Where 

 does it act ? It acts wherever there is the medulla 

 above mentioned ; and that whether the limb is 

 yet joined to a living animal, or whether it be re- 

 cently detached from it ; as the heart of a viper or 

 frog will renew its contractions, when pricked 

 with a pin, for many minutes of time after its ex- 

 fection from the body. Does it act any where 

 elfe ? No ; then it certainly exifts in this part of 

 (pace, and no where elfe ; that is, ir hath figure ; 

 namely, the figure of the nervous fyilem, which is 

 nearly the figure of the body. When the idea of 

 iolidity is excited, as above explained, a part of 

 the exteniive organ of touch is comprefled by fome 

 external body, and this part of the fenibrium fo 

 compreffed exactly refembles in figure the figure. of 

 the body that compreffcd it. Hence, when we 

 acquire the idea of folidity, we acquire at the fame 

 time the idea of FIGURE; and this idea of figure, 

 or motion of a part of the organ of touch, exactly 

 refembles In its figure the figure of the body that 

 occafions it ; and thus exactly acquaints us with 

 this property of the external world. 



Now, as the whole univerfe with all its parts 

 poftefies a certain form or figure, if any part of it 

 moves, that form or figure of the whole is varied : 

 hence, as MOTION is no other than a perpetual va- 

 riation of figure, our idea of motion is alfo a real 

 refemblance of the motion that produced it. 



It may be faid in objection to this definition of 

 motion, that an ivory globe may revolve on its 

 axis, and that here will be a motion without change 

 of figure. But the figure of the particle % on one 

 iide of this globe is not the fame figure as the figure 

 of/ on the other fide-, any more than the particles 

 themfelves are the fame, though they are fimilar 



figures ; 



