PHYSICS IN 1913 615 



structure, and Nishikawa and Ono have shown that many 

 fibrous substances, such as asbestos and bamboo, give patterns 

 of a rather different type. 



Not very much progress has been made in the general 

 theory of radiation during the past year. Since Poincare in 

 191 2 showed that no law of continuous emission of radiant 

 energy could account for the form of the radiation curve in 

 the short wave-lengths, all attention has been concentrated 

 on the application of Planck's quantum theory, which asserts 

 that radiant energy cannot be emitted continuously in amounts 

 of a completely arbitrary magnitude, but only in whole numbers 

 of discrete units, or quanta, of energy, whose magnitude is a 

 constant, h, times the frequency number of the given radiation. 

 The universal constant h is often referred to as Planck's 

 constant. In its present form the theory does not exclude 

 continuous waves of energy in the ether, or the continuous 

 absorption of energy, as without waves in the ether of the 

 nature assumed in the classical electromagnetic theory it seems 

 impossible at present to account for the phenomena of polarisa- 

 tion and interference. The polarisation of light by crystals 

 would seem to depend on an interaction between the matter 

 and radiant energy which does not take place quantum fashion. 

 The quantum theory presents grave difficulties in the way of 

 a satisfactory physical interpretation, especially over the 

 question of absorption, but its justification lies in the brilliant 

 agreement which many of its consequences show with experi- 

 mental results at present inexplicable on the older theories. 

 The older Hamiltonian equipartition of energy among the 

 degrees of freedom has proved insufficient; Jeans has abandoned 

 his idea that its predictions fail because the steady state is 

 never realised. The simplest of the present methods of deducing 

 the radiation formula is to count the number of degrees of 

 freedom of the equilibrium radiation by means of the number of 

 different stationary waves set up in an enclosure with re- 

 flecting walls (Jeans, Rayleigh), and distribute the energy 

 among them in quanta of magnitude proportional to the 

 frequencies according to a probability law. Debye, by an 

 extension of this method, has obtained a formula connecting 

 the specific heat of metals with the temperature, agreeing re- 

 markably well with experiment. He assumes that the heat 

 energy consists of elastic vibrations of the atoms about positions 

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