428 SCIENCE PROGRESS. 



no After, in the sense of our world ; the tree could return 

 again to the sapling and the sapling to the seed, the butter- 

 fly transform itself once more into the caterpillar, and the 

 old man become again a babe. For the fact that this does 

 not occur, the mechanical conception of the world has no 

 explanation to offer, and can have none on account of the 

 already mentioned property of mechanical equations. The 

 evident irreversibility of actual natural phenomena proves, 

 therefore, the existence of processes which cannot be 

 represented by mechanical equations, and with this state- 

 ment the judgment on scientific materialism is passed. 



We must accordingly, and this appears to follow with 

 absolute certainty from these considerations, give up all 

 hope of getting a clear idea of the physical world by refer- 

 ring phenomena to an atomistic mechanics. But, perhaps 

 one of you will say, what means shall we have left of 

 picturing to ourselves what really occurs in nature when 

 the conception of atoms in motion is abolished ? To such a 

 question I would answer : Thou shalt not make unto thyself 

 any image or likeness. Our task is not to view the world in 

 a more or less bedimmed and crooked mirror, but as directly 

 as the nature of our minds will permit. To co-ordinate 

 realities, i.e., definite and measurable quantities, so that 

 when certain of them are given the others can be deduced, 

 is the problem set before science, and this problem cannot 

 be solved by assuming as substratum any hypothetical 

 analogue, but only by the determination of the mutual 

 relations existing: between measurable magnitudes. 



Undoubtedly this way is long and tiring, yet it is the 

 only permissible one. But we need not tread this path 

 with bitter self-renunciation hoping that it will finally lead our 

 grandchildren to the longed-for summit. No, it is we who 

 are the fortunate ones, and the most hopeful bequest which 

 the departing century can bestow on the one that is just 

 dawning is the replacement of the mechanical by the "ener- 

 getical " conception of the universe. 



I consider it of the greatest importance to state here 

 that all this is by no means a novelty, a production of 

 to-day. No, for half a century it has, though unrecognised, 



