S2 PRODUCTION Sect. XIV. 2. 2. 



of the whole is varied : hence, as motion is no other than a per- 

 petual variation of figure, our idea of motion is alfo a real re- 

 femblance 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 parti- 

 cle x on one fide of this globe is not the fame figure as the figure 

 of y on the other fide, any more than the particles themfelves 

 are the lame, though they are fimilar figures ; and hence they 

 cannot change place with each other without difturbing or 

 changing the figure of the whole. 



Our idea of time is from the fame fource, but is more ab- 

 itracted, as it includes only the comparative velocities of thefe 

 variations of figure ; hence if it be afked, How long was this 

 book in printing ? it may be anfwered, Whilft the fun was 

 palling through Aries. 



Our idea of place includes only the figure of a group of 

 bodies, not the figures of the bodies themfelves. If it be afked 

 where is Nottinghamfhire, the anfwer is, it is furrounded by 

 Derbyfhire, Lincolnfhire, and Leicefterfhire ; hence place is our 

 idea of the figure of one body furrounded by the figures of other 

 bodies. 



The idea of space is a more abftratled idea of place exclu- 

 ding the group of bodies. 



The idea of number includes only the particular arrange- 

 ments, or diftributions of a group of bodies, and is therefore on- 

 ly a more abftracfted idea of the parts of the figure of the group 

 of bodies ; thus when I fay England is divided into forty coun- 

 ties, I only fpeak of certain divifions of its figure. 



Hence arifts the certainty of the mathematical fciences, as 

 they explain thefe properties of bodies, which are exactly re- 

 fembled by our ideas of them, whilft we are obliged to collect 

 almoft all our other knowledge from experiment ; that is, by 

 obferving the effects exerted by one body upon another. 



I feel myfelf much obliged by the accurate attention given to 

 the firft volume of Zoonomia, and by the ingenious criticifms 

 bellowed on it, by the learned writers of that article both in 

 the Analvtical and Emjlifh Reviews. Some circumftances, in 

 which their fentiments do not accord with thofe exprefTed in the 

 work, I intend to reconfider, and to explain further at fome fu- 

 ture time. One thing, in which both thefe gentlemen feem to 

 difient from me, I fhall now mention, it is concerning the man- 

 ner, in which we acquire the idea of figure ; a circumftance of 

 great importance in the knowledge of our intellect, as it fhews 

 the caufe of the accuracy of our ideas of motion, time, fpace, 



• number, 



