November 20, 1914] 



SCIENCE 



727 



purpose is to stay. It not only tells us all we 

 know of the distribution of energy in the 

 black body spectrum in its thermal relations, 

 but it gives us, indirectly, perhaps the most 

 accurate data at hand of the number of mol- 

 ecules per normal cubic centimeter of the gas, 

 of the mean translational energy of its mol- 

 ecules, of the molecular mass, of the Boltz- 

 mann entropy constant, even of the charge of 

 the electron or electric atom itself. Under 

 the guidance of Nernst it has created new 

 chapters in the treatment of specific heats at 

 low temperatures, their evanescence at the abso- 

 lute zero of temperatures, the evanescence of 

 the specific electrical resistance at zero, all 

 more or less bearing on Dulong and Petit's 

 law. Not less vital is the introduction of the 

 new universal constant hitherto not even sus- 

 pected, the " Wirkungs quantum," an equiva- 

 lent of the Hamiltonian integral of action. 

 Here then is a departure from continuity pos- 

 tulated for energy, which will hereafter oper- 

 ate with definite finite elements only. The con- 

 dition of occurrence of such elements in any 

 definite relations, can for this reason be speci- 

 fied as a ease of probability. 



Of the Planck molecular oscillators I must 

 speak briefly. If operating continuously under 

 the established electromagnetic laws they lead 

 to the impossible distributions of energy in the 

 spectrum investigated by Eayleigh and Jeans. 

 But if emitting only, when their energy con- 

 tent is a whole number of energy elements, a 

 case thus involving the entropy probability 

 of Boltzmann, Wien's law and the numerical 

 data referred to are deducible with astounding 

 precision. 



This then is the peculiar state of physics 

 to-day. The appearance at the very footlights 

 of the stage, of a new constant, the meaning 

 of which nobody knows, but whose importance 

 is incontestable. Moreover energy is seen 

 there under an entirely new role. Grasping 

 at greater freedom she has hopelessly involved 

 herseK in the meshes of the doctrine of prob- 

 ability. There was a time, the time antedating 

 Mayer (1840^2) and Joule (1843), Kelvin 

 and Clausius, when to speak of indestructible 

 energy would have been rash. It was a glori- 



ous epoch when she first appeared in the full 

 dignity of her conservative and infinite con- 

 tinuity. In contrast with this, the energy of 

 the present day is scarcely recognizable. Not 

 only has she possessed herself of inertia, but 

 with ever stronger insistence she is usurping 

 the atomic structure once believed to he 

 among the very insignia of matter. Contem- 

 poraneously, matter itseK, the massive, the in- 

 destructible, endowed by Lavoisier with a sort 

 of physical immortality, recedes ever more 

 into the background among the shades of 

 velocity and acceleration. 



But the single equation of nature, aimed at 

 by Lagrange and Hamilton, by Weber and 

 Maxwell in their several ways, has nevertheless 

 throughout all this turmoil reached a more 

 profound significance and now even holds 

 dynamics, awkwardly it is true but none the 

 less inexorably, in its grasp. That it is not 

 complete, that it never can be complete, is 

 admitted (for the absolute truth poured into 

 the vessel of the human mind would probably 

 dissolve it) ; but that it is immeasurably more 

 complete to-day than it was yesterday is as 

 incontrovertably true as it is inspiring. 



Gael Barus 



Brown University, 

 Providence, R. I. 



CONTEMPOBABY UNIVEBSITY FBOBLEMS^ 

 The story of Glark University during the 

 quarter century of its existence, the close of 

 which we celebrate to-day with the alumni, 

 under the inspiring guidance of Dr. French 

 and his committee, has in some respects no 

 parallel in academic history. Especially the 

 first few years of our annals have both brighter 

 and darker pages than I can find in the rec- 

 ords of any university. Thirteen of us in- 

 structors had taught or taken degrees at the 

 Johns Hopkins, and we left that institution, 

 which had added a new and higher story to the 

 American university, when it was at the very 

 apex of its prosperity and hence were naturally 



1 Address given on the occasion of the celebra- 

 tion of the twenty-fifth anniversary of Clark Uni- 

 versity by Dr. G. Stanley Hall, president of the 

 university. 



