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SCIENCE 



[N. S. Vol. XXXVIII. No. 977 



rightly neglect them, in order to do their 

 proper work, but philosophers can not. 



So philosophers have begun to question 

 some of the larger generalizations of sci- 

 ence, and to ask whether in the effort to be 

 universal and comprehensive we have not 

 extended our laboratory inductions too far. 

 The conservation of energy, for instance — 

 is it always and everywhere valid; or may 

 it under some conditions be disobeyed? 

 It would seem as if the second law of 

 thermodynamics must be somewhere dis- 

 obeyed — at least if the age of the universe 

 is both ways infinite — else the final eon- 

 summation would have already arrived. 



Not by philosophers only, but by scien- 

 tific men also, ancient postulates are being 

 pulled up by the roots. Physicists and 

 mathematicians are beginning to consider 

 whether the long known and well-estab- 

 lished laws of mechanics hold true every- 

 where and always, or whether the New- 

 tonian scheme must be replaced by some- 

 thing more modem, something to which 

 Newton's laws of motion are but an ap- 

 proximation. 



Indeed a whole system of non-Newtonian 

 mechanics has been devised, having as its 

 foundation the recently discovered changes 

 which must occvir in bodies moving at 

 speeds nearly comparable with that of 

 light. It turns out in fact that both shape 

 and mass are functions of velocity. As the 

 speed increases the mass increases and the 

 shape is distorted, though under ordinary 

 conditions only to an infinitesimal extent. 



So ^ar I agree; I agree with the state- 

 ment of fact; but I do not consider it so 

 revolutionary as to overturn Newtonian 

 mechanics. After all, a variation of mass 

 is familiar enough, and it would be a great 

 mistake to say that Newton's second law 

 breaks down merely because mass is not 

 constant. A raindrop is an example of 

 variable mass ; or the earth may be, by rea- 



son of meteoric dust ; or the sun, by reason 

 of radio-activity; or a locomotive, by rea- 

 son of the emission of steam. In fact, 

 variable masses are the commonest, for 

 friction may abrade any moving body to a 

 microscopic extent. 



That mass is constant is only an approx- 

 imation. That mass is equal to ratio of 

 force and acceleration is a definition, and 

 can be absolutely accurate. It holds per- 

 fectly even for an electron with a speed 

 near that of light; and it is by means of 

 Newton's second law that the variation of 

 mass "with velocity has been experimentally 

 observed and compared with theory. 



I urge that we remain with, or go back 

 to, Newton. I see no reason against re- 

 taining all Newton's laws, discarding noth- 

 ing, but supplementing them in the light 

 of further knowledge. 



Even the laws of geometry have been 

 overhauled, and Euclidean geometry is 

 seen to be but a special case of more funda- 

 mental generalizations. How far they 

 apply to existing space, and how far time 

 is a reality or an illusion, and whether it 

 can in any sense depend on the motion or 

 the position of an observer : all these things 

 in some form or other are discussed. 



The conservation of matter also, that 

 main-mast of nineteenth century chemis- 

 try, and the existence of the ether of space, 

 that sheet-anchor of nineteenth century 

 physics — do they not sometimes seem to be 

 going by the board? 



Professor Schuster, in his American lec- 

 tures, commented on the modern receptive 

 attitude as follows :- 



The state of plasticity and flux — a healthy state, 

 in my opinion — in which scientific thought of the 

 present day adapts itself to almost any novelty, 

 is illustrated by the complacency with which the 

 most cherished tenets of our fathers are being 

 abandoned. Though it was never an article of 

 orthodox faith that chemical elements were im- 

 mutable and would not some day be resolved into 



