A N D G R O W T H. 47 



ed by Des Cartes. But it is, at leafl:, an unte- 

 nible project; and, though it were othervvife, 

 \vc arc unable to put it in execution. Thefe 

 mechanical principles are, ihe extenfion of inat- 

 ter, its impenetrabiliry, its motion, its external 

 figure, i»s divilibility, the communication of mo- 

 tion by impuifc, by the action of fprings, &c. 

 Thefe ideas we have acquired by cur fenies, and 

 we regard them as principles, becaufe they are 

 general and common to all matter. But are we 

 certain that matter poffeiTcs no other qualities ? 

 Ought we not rather to believe that thefe qua- 

 lities, which we ailume for principles, are only 

 modes of perception ; and that, if the confor- 

 mation of our fenfes were different, we would 

 recognize qualities in matter very different from 

 thole above enumerated ? It is prcfumptuous to 

 deny every quality to matter but thofe we are 

 acquainted with. Many general qualities, per^ 

 haps, remain to be difcovered ; and many may 

 cxift Vv'hich will for ever elude human difcern- 

 mcnt. The caufe of impulfion, of cohelion, or 

 of any other mechanical principle, will always 

 continue to be equally infcrutable as that of at- 

 traction, or of any other general quality. Hence 

 it may be concluded, that mechanical principles 

 are nothing elfe than general effects which ex- 

 perience has enabled us to remark in matter ; 

 and that, whenever we fhall difcover, cither by 

 reflexion, by analogy, or by experience, a new 

 general cffedt, it will become a new mechanical 



principle, 



