July 24, 1914] 



SCIENCE 



117 



able to account correctly for the above law 

 for series of lines in the spectrum. 



We may appreciate Poincare 's criticism — 

 On a quelque peine a accepter cette conception, 

 qui a je ne sais quoi d'artifieiel. 



Inasmuch as physicists endeavor to ex- 

 plain magnetism in terms of revolving 

 electrons, there is a lack of simplicity, and 

 there is an inconsistency, in introducing 

 elemental magnets inside the atom. Never- 

 theless, it must be admitted that Weiss has 

 found remarkable evidence for the concep- 

 tion of magnetons or elemental unit magnets, 

 producing intra-molecular fields reaching 

 to millions of Gauss units, far transcending 

 any produced by our most powerful electro- 

 magnets, and difficult to explain by revolv- 

 ing electrons. 



Again to quote Poincare — 

 Qu' est-ce maintenant qu'un magneton? Est-ce 

 quelque chose de simple? Non, si I'on ne veut pas 

 reuoncer a I'hypothfese des courants particulaires 

 d'AmpSre; un magn6ton est alors un tourbillon. 

 d 'electrons, et voila notre atome qui complique de 

 plus en plus. 



Perhaps the hypothesis of Bohr, ex- 

 plained later, may overcome the difficulty, 

 but for some time to come the more pru- 

 dent wiU suspend judgment on the 

 magneton. 



Eecently there has been nothing short of 

 a revolution in physics. In certain do- 

 mains, the leading workers and thinkers 

 have deliberately abandoned the classical 

 dynamics and electro-dynamics, and made 

 suppositions which are in direct opposition 

 to these. This startling change may per- 

 haps be justified by the fact that the 

 famous laws and equations were based on 

 large scale experiments, so that they do not 

 necessarily apply to conditions within the 

 atom. Those who put forward and make 

 use of the new hypotheses, men like Planck 

 and Lorentz, Poincare and Jeans and 

 others, appear to do so with reluctance, like 

 a retiring army forced from one position to 



another. Others, like Eayleigh and Larmer, 

 appear to regard the whole movement with 

 misgivings, and some endeavor, like Walker 

 and Callendar, to find a way out. There is 

 a young school who go joyfully forward, 

 selecting and suggesting somewhat wild 

 hypotheses, and yet attaining an unex- 

 pected measure of success by their appar- 

 ently reckless methods. 



The main phenomena to which the new 

 mechanics have been applied are the radia- 

 tion within an enclosure, and the distribu- 

 tion of energy therein; the high speed of 

 electrons ejected from matter by ultra- 

 violet light, or by Rontgen rays, or by the 

 gamma or penetrating rays from radio- 

 active substances, or as I suggest that we 

 call them, from radiants; the atomic heat 

 of elements, so admirably handled by 

 Debye; the residual energy at low tem- 

 peratures ; and the constitution of the atom. 



Space prevents us from considering 

 more than the last of these. 



The first step towards the new method 

 was taken by Planck when he saw the neces- 

 sity of explaining why the energy of short 

 wave radiation is some hundred millionth 

 part of that demanded by classical dynam- 

 ics. He made the supposition that energy 

 is not indefinitely divisible, but he did not 

 assume that it was atomic. He actually 

 imagined that energy was emitted from 

 oscillators in exact multiples of hn, where 

 n is the frequency of the oscillation and h 

 is a universal constant (Planck's) with a 

 value 6.5 X 10"" erg second. The magni- 

 tude of the energy quantum is thus pro- 

 portional to the frequency. 



This quantum hypothesis has spread like 

 fire during a drought. It pervades the 

 scientific journals. No physicist has pre- 

 tended to explain or understand it, for, as 

 Jeans says, the lucky guess has not yet 

 been made. Nevertheless, it appears that 

 "h" has truth underlying it, and that it 



