1 72 Mr. J. J. Walerstone's Expositioti of 



perties by which it is distinguished, and that they may both 

 be examples of the same elementary force exhibited through 

 different media? 



Such conjectures, although derived from an extensive and 

 minute survey of the facts elicited by experiment, are yet pre- 

 vented from ever becoming of practical utility, by our igno- 

 rance of motion. How does it originate ? In what manner are 

 its effects so complex, and its development so varied ? These 

 are questions which first naturally arise, and indeed compre- 

 hend all that can form the object of philosophic inquiry. The 

 first, relating to its origin, has often been investigated both 

 by physical and metaphysical authors : many abstract specu- 

 lations have engaged the attention of the latter, but they uni- 

 versally partake of the usual defects of that science, referring 

 every effect to a primary cause, which in whatever way it may 

 be defined in words, fails to convey any definite conception or 

 satisfactory meaning to the mind. Disgusted with such idle 

 and inconclusive reasoning, and despairing of being practically 

 useful to science by prosecuting such inquiries, it is not sur- 

 prising that philosophers have never devoted themselves to 

 investigate this subject on simple physical principles, by the 

 application of which alone we may expect to further the pro- 

 gress of natural philosophy. 



Tvvo opinions are entertained by philosophers relating to 

 this subject : the first, that the absolute quantity of motion in 

 the universe is always the same, suffering neither the smallest 

 increase or diminution; the second, that " motion is much 

 more apt to be lost than got*," and that therefore " some other 

 principle is necessary for conserving it, " to supply the con- 

 tinued loss incurred " by reason of the tenacity of fluids and 

 attrition of their parts, and the weakness of elasticity in solids." 

 The former doctrine was maintained by the Cartesians, who 

 defended their opinions by the aid of such extravagant hypo- 

 theses, that Newton and his followers, by showing the obvious 

 absurdity of their demonstration, adopted the contrary belief, 

 not so much from the satisfactory proofs brought forward in 

 support of it, as because it was contradictory to the great 

 principle of Des Cartes, which was naturally supposed to have 

 partaken of the general fallacy of his vortical system. Later 

 philosophers, although ardent admirers of Newton and his 

 philosophy, have yet rejected his doctrine, and in refutation 

 of it have brought forward mathematical proofs of its fallacy, 

 which if not conclusive, are at least plausible and ingenious. 

 To prove either hypothesis however, involves reasoning distinct 

 from the abstract comparison of quantities. An intimate ac- 



* 30th Query, Newton's Optics. 



quaintance 



