Sect. XXXIX. 12. 2. GENERATION. 439 



effect. For example, a moving ivory ball could not proceed 

 onwards, unlefs it had previoufly begun to proceed ; or unlefs an 

 impulfe had been previoufly given it ; which previous motion or 

 impulfe conftitutos a part of the laft fituation of things. 



As the effects produced in this moment of time become 

 caufes in the next, we may confider the progreffive motions of 

 objects as a chain of caufes only ; whofe firft link proceeded 

 from the great Creator, and which have exifted from the begin- 

 ning of the created univerfe, and are perpetually proceeding. 



2. Thefe caufes may be conveniently divided into two kinds, 

 efficient and inert caufes, according with the two kinds of enti- 

 ty fuppofed to exifl in the natural world, which may be termed 

 matter and fpirit, as propofed in Sect. I. and further treated of in 

 Seel:. XIV. The efficient caufes of motion, or new configura- 

 tion, confift either of the principle of general gravitation, which 

 actuates the fun and planets ; or of the principle of particular 

 gravitation, as in electricity, magnetifm, heat j or of the princi- 

 ple of chemical affinity, as in combuftion, fermentation, combi- 

 nation ; or of the principle of organic life, as in the contraction 

 of vegetable and animal fibres. The inert caufes of motion, or 

 new configuration, confift of the parts of matter, which are in- 

 troduced within the fpheres of activity of the principles above 

 defcribed. Thus, when an apple falls on the ground, the prin- 

 ciple of gravitation is the efficient caufe, and the matter of the 

 apple-tree the inert caufe. If a bar of iron be approximated 

 to a magnet, it may be termed the inert caufe of the motion, 

 which brings thefe two bodies into contact ; while the magnetic 

 principle may be termed the efficient caufe. In the fame man- 

 ner the fibres, which conftitute the retina, may be called the in- 

 ert caufe of the motions of that organ in vifion, while the fen- 

 forial power may be termed the efficient caufe. 



3. Another more common diftribution of the perpetual chain 

 of caufes and effects, which conftitute the motions, or chang- 

 ing configurations, of the natural world, is into active and paf- 

 five. Thus, if a ball in motion impinges againft another ball at 

 reft, and communicates its motion to it, the former ball is faid 

 to act, and the latter to be acted upon. In this fenfe of the 

 words a magnet is faid to attract iron ; and the prick of a fpur 

 to ftimulate a horfe into exertion ; fo that in this view of the 

 works of nature all things may be faid either fimply to exift, or 

 to exift as caufes, or to exift as effects 5 that is, to exift either 

 in an active or pa (live ftate. 



This distribution of objects and their motions, or changes 

 of pofition, has been found fo convenient for the purpofes of 

 common life, that on this foundation refts the whole conftruc- 



m 



