60 ULTIMATE SCIENTIFIC IDEAS. 



sensibly until it becomes infinitesimal ; and many will think 

 equally possible to pass in thought from infinitesimal motion 

 to no motion. But this is an error. Mentally follow out the 

 decreasing velocity as long as you please, and there still 

 remains some velocity. Halve and again halve the rate of 

 movement for ever, yet movement still exists; and the 

 smallest movement is separated by an impassable gap from 

 no movement. As something, however minute, is infinitely 

 great in comparison with nothing ; so is even the least con- 

 ceivable motion, infinite as compared with rest. The 

 converse perplexities attendant on the transition from Rest 

 to Motion, need not be specified. These, equally with the 

 foregoing, show us that though we are obliged to think of 

 such changes as actually occurring, their occurrence cannot 

 be realized. 



Thus neither when considered in connexion with Space, 

 nor when considered in connexion with Matter, nor when 

 considered in connexion with Rest, do we find that Motion 

 is truly cognizable. All efforts to understand its essential 

 nature do but bring us to alternative impossibilities of 

 thought. 



§ 18. On lifting a chair, the force exerted we regard as 

 equal to that antagonistic force called the weight of the 

 chair; and we cannot think of these as equal without think- 

 ing of them as like in kind; since equality is conceivable 

 only between things that are connatural. The axiom that 

 action and reaction are equal and in opposite directions, 

 commonly exemplified by this very instance of muscular 

 effort versus weight, cannot be mentally realized on any 

 other condition. Yet, contrariwise, it is incredible that the 

 force as existing in the chair really resembles the force as 

 present to our minds. It scarcely needs to point out that the 

 weight of the chair produces in us various feelings according 

 as we support it by a single finger, or the whole hand, or the 

 leg; and hence to argue that as it cannot be like all these 



