212 Necessary Limitation of the Doctrine of the 



around us : each will produce such motion, and will be accu- 

 rately and completely measured by the amount of motion 

 into which it is thus capable of resolving itself. 



This doctrine, of the unity of the general forces of nature, 

 I do not propose to dispute. It is a doctrine of the most 

 interesting and beautiful kind ; and if not fully proved, — and 

 some eminent physicists still demur to the reception of it — 

 it yet furnishes so many singular and ingenious explanations 

 of phenomena, that one is tempted to overlook its want of 

 complete demonstration, and acquiesce, perhaps by antici- 

 pation, in the conclusion which affirms it. And yet there 

 seems to be a limitation of its scope, arising out of the 

 necessary relation of this to another equally important phys- 

 ical doctrine of our day — the indestructibility of matter. 



It is affirmed with equal certainty that, in all the varied 

 round of changes taking place among the particles and com- 

 binations of matter, no slightest atom or molecule of it is 

 ever lost. Every chemical change is but a combination, or 

 a resolution, of the particles of a mass ; but these particles 

 are ever the same in number, in weight, and in attraction. 

 No one of them can by any possibility ever be put out of 

 existence. The amount of matter is as constant as the 

 amount of force in the universe ; and both are alike beyond 

 our power to alter or reduce. 



It has not hitherto been observed, however, that the one 

 of these doctrines imposes by necessity a limit upon the 

 scope of the other ; and it is with the object of calling atten- 

 tion to this restriction, that the present paper is offered. 

 Before proceeding, however, to point out the limitation 

 referred to, it may be well to endeavor to gain a more exact 

 appreciation of the doctrine already desci-ibed, of the con- 

 vertibility of force. What is meant by it ? 



Strictly speaking, this view is often not accurately stated 

 in the ordinar}^ language of science. " Heat," according to 

 Tyndall's just and happy statement of the fact, " is a mode 

 of motion ;" it is a motion of the molecules, instead of a 



