528 



SCIENCE 



[N. S. Vol. XXXI. No. 797 



Let us distinguish carefully between the 

 observed facts of nature and those tempt- 

 ing pictures of the human mind which we 

 only too easily create and are only too apt 

 to worship. 



Among the realities of mechanics are to 

 be mentioned bodies in motion, liquids 

 flowing, springs changing length; among 

 the abstractions of the subject— helpful 

 and needful abstractions— but abstractions 

 nevertheless— are to be numbered the 

 forces, velocities and accelerations of these 

 bodies. Only by understanding these mat- 

 ters and by drawing a sharp line here 

 shall we avoid Maxwell's "den of the 

 metaphy.sician. ' ' 



It is not infrequently that one finds a 

 clever metaphysician in the orthodox man 

 of empirical science ; and I am free to con- 

 fess myself unable to say whether the ma- 

 jority of the criticisms of the foundations 

 of our science are due to the physicist or 

 the philosopher; but in either ease the 

 critic speaks as a metaphysician. As an 

 illustration consider the penetrating criti- 

 cisms of the foundations of rational dynam- 

 ics recently given by Mr. Norman Camp- 

 bell,' who shows that the science of 

 mechanics is so loaded with assumptions 

 that the experimental verification of its 

 laws is utterly hopeless. 



IV. PRELIMINARY DISCUSSIONS 



Fourthly, metaphysics has, I believe, 

 rendered distinct service in giving us cer- 

 tain helpful preliminary discussions. In- 

 deed, it is the history of many of the 

 special sciences, such as psychology and 

 sociology, that they were at one time de- 

 partments of philosophy— but now, having 

 shown themselves amenable to experiment 

 or observation and subject to the "reign 

 of law," are established as kingdoms of 

 their own. The very notion of mechanical 



'Phil. Mag., January, 1910. 



law is at least as old as Thales— 600 b.c. — 

 whose idea it was, in common with Anaxi- 

 mander, Anaximenes and Heraclitus, that 

 the variety of things is due to "a single 

 material cause, corporeal, endowed with 

 qualities and capable of self-transforma- 

 tion."" Eidiculous and absurd as this 

 sounds to us, it nevertheless contains the 

 fundamental conception of mechanical law, 

 and made it easier for later men to adopt 

 more useful hypotheses. 



The history of the atomic theory illus- 

 trates well the value of this contribution. 

 The atom of Democritus— a purely meta- 

 physical structure— difiiers in no essential 

 respect from the modern atom up to the 

 year 1738 when Daniel Bernoulli initiated 

 the kinetic theory of gases. 



The contention of Anaxagoras that all 

 bodies are really continuous has also been 

 of the utmost help : Poisson adopted it in 

 toto in his mechanics; it was employed in 

 electrical science up to the date of Helm- 

 holtz's Faraday lecture, 1881, and it is 

 to-day practically adopted in all discus- 

 sions of hydrodynamics. 



MaxwelP^ goes so far as to say : 



In the earliest times the most ancient philos- 

 ophers whose speculations are known to us seem 

 to have discussed the ideas of number and of 

 continuous magnitude, of space and time, of mat- 

 ter and motion with a native power of thought 

 which has probably never been surpassed. 



It was a really profound insight into the 

 nature of pure mathematics that led cer- 

 tain participants in the relativity discus- 

 sion, at the last meeting of this society, to 

 place in the same class the metaphysician 

 and the mathematician ; the new grouping 

 of studies at Harvard College does the 

 same; each of these subjects is concerned 

 neither with phenomena of any kind, nor 

 with individual purposes, but with those 



" " Encyclopedia Britannica," 23, 219. 

 " " Encyclopedia Britannica," art. Atom. 



