1 74 CORRELA TION OF PHYSICAL FOR CES. 



hension the impossibility of this is not self-evident : if the 

 initial weight is to be raised by the force it has itself gene- 

 rated, it must necessarily generate a force greater than that 

 of its own weight or centripetal attraction ; in other words, it 

 must be capable of raising a weight heavier than itself ; so 

 that, setting aside the resistance of friction, &c., a weight, to 

 produce perpetual recurrent motion, must be heavier than an 

 equal weight of matter, in short, heavier than itself. 



Suppose two equal weights at each end of an equi-armed 

 lever, there is no motion ; cut off a fraction of one of them, 

 and it rises while the other falls. How, now, is the lesser 

 weight to bring back the greater without any extraneous 

 application of force ? If, as is obvious, it cannot do so in this 

 simple form of experiment, it is a fortiori more impossible if 

 machinery be added, for increased resistances have then to 

 be overcome. Can we again mend this by employing any 

 other force ? Suppose we employ electricity, the initial 

 weight in descending turns a cylinder against a cushion, and 

 so generates electricity ; to make this force recurrent, the 

 electricity so generated must, in its turn, raise the initial 

 weight, or one heavier than it, i.e. the initial weight must, 

 through the medium of the electricity it generates, raise a 

 weight heavier than itself. The same problem, applied to any 

 other forces, will involve the same absurdity ; and yet, simple 

 as the matter seems, the world is hardly yet disabused of an 

 idea little removed from superstition. 



But the importance of the deductions to be derived from 

 the negation of perpetual motion seems scarcely to have 

 impressed philosophers, and we only find here and there a 

 scattered hint of the consequences necessarily resulting from 

 that which to the thinking mind is a conviction. Some of 

 these I have ventured to put forward in the present Essay, 

 but many remain, and will crowd upon the mind of those who 

 pursue the subject. Does not, for instance, the impossibility 

 of perpetual motion, when thought out, involve the de- 

 monstration of the impossibility, to which I have previously 

 alluded, of any event identically recurring ? 



The pendulum in vacua, at each beat, leaves a portion of 

 the force which started it, in the form of heat at its point of 



