152 Mr, W. H, Grove, on Inferences from [Jan. 25, 



WEEKLY EVENING MEETING, 



Friday, January 25, 1856. 



Sir Benjamin Collins Brodie, D.C.L. F.R.S. Vice-President, 

 in the Chair. 



W. R. Grove, Esq. Q.C. F.R.S. M.R.I. 



Inferences from the Negation of Perpetual Motion. 



Scattered among the writings of philosophers will be found 

 allusions to the subject of perpetual motion, and here and there are 

 arguments like the following ; such a phenomenon cannot take place, 

 or such a theory must be fallacious, because it involves the idea of 

 perpetual motion : thus Dr. Roget advanced as an argument against 

 the contact theory of electricity, as originally propounded, that if 

 mere contact of dissimilar metals, without any chemical or molecular 

 change, could produce electricity, then as electricity could, in its 

 turn, be made to produce motion, we should thus get perpetual 

 motion. 



It may be well to define, as far as such a definition is possible, 

 what is commonly meant by the term perpetual motion. In one sense, 

 all motion, or rather all force, is perpetual ; for example, if a clock 

 weight be wound up, it represents the force derived from the muscles 

 of the arm which turns the key, the muscles again derive force 

 indirectly from the chemical action of the food, and so on. As the 

 weight descends it conveys motion to the wheels and pendulum ; the 

 former giving force off in the form of heat from friction, the latter 

 communicating motion to the air in contact with it, thence to the 

 case of the clock, thence to the air of the room, — proved in a very 

 simple manner by the ticking heard, which is in fact, a blow to the 

 organ of hearing. Although ultimately lost to our senses, there is 

 no reason to suppose that the force is ever in fact lost. The weight 

 thus acting, reaches the ground quietly, and produces no effect at 

 the termination of its course. 



If, instead of being allowed to communicate its force to the works 

 of the clockjthe weight be allowed to descend suddenly, as by cutting 

 the string by which it is suspended, it strikes the floor with a force 

 which shakes the house ; and thus conveys, almost instantaneously, 

 the amount of force which would be gradually dissipated, though 

 not ultimately consumed, by the clock in a week or nine days. 



This idea, however, of the perpetuity of force, is not what is 



