CONCLUDING REMARKS. 173 



bodies in which this parity of force has been discovered, 

 though in themselves numerous, are small compared with the 

 exceptions, and, therefore, this point can only be indicated as 

 promising a generalisation, should subsequent researches alter 

 our knowledge as to the elements and combining equivalents 

 of matter. 



With regard to what may be called dynamic equivalents, 

 i.e. the definite relation of the motive action of these varied 

 forces upon equivalents of matter, the difficulty of establish- 

 ing them is still greater. If the proposition which I stated at 

 the commencement of this paper be correct, that motion may 

 be subdivided or changed in character, so as to become heat, 

 electricity, &c., it ought to follow that when we collect the 

 dissipated and changed forces, and re-convert them, the initial 

 motion, minus an infinitesimal quantity, affecting the same 

 amount of matter with the same velocity, should be repro- 

 duced, and so of the changes in matter produced by the other 

 forces ; but the difficulties of proving the truth of this by 

 experiment will, in many cases, be all but insuperable ; we 

 cannot imprison motion as we can matter, though we may 

 to some extent restrain its direction. 



The term perpetual motion, which I have not unfrequently 

 employed in these pages, is itself equivocal. If the doctrines 

 here advanced be well founded, all motion is, in one sense, per- 

 petual. In masses whose motion is stopped by mutual con- 

 cussion, heat or motion of the particles is generated ; and thus 

 the motion continues, so that if we could venture to extend 

 such thoughts to the universe, we should assume the same 

 amount of motion affecting the same amount of matter for 

 ever. Where force is made to oppose force, and produce 

 static equilibrium, the balance of pre-existing equilibrium is 

 affected, and fresh motion is started equivalent to that which 

 is withdrawn into a state of abeyance. 



But the term perpetual motion is applied, in ordinary 

 parlance (and in such sense I have used it), to a perpetual 

 recurrent motion, e.g., a weight which by its fall would turn a 

 wheel, which wheel would, in its turn, raise the initial weight, 

 and so on for ever, or until the material of which the machine 

 is made be worn out. It is strange that to common appre- 



