390 Prof. E.Wiedemann on the 



of the molecules in their material portions perform the motions 

 which correspond to the store of luminous energy. 



The store of luminous energy is emitted as light in the 

 course of time. It is originally present in the form of vibra- 

 tions whose maximum vis viva is exactly equal to this store of 

 energy. The assumption that it is present in the first instance 

 as potential energy, depending upon rearrangements of the 

 atoms and molecules, presents great difficulties, especially in 

 the case of the monatomic gases. 



If we denote by v the velocity with which the vibrating 

 molecules pass through the position of equilibrium, by a the 

 amplitude, and by T the period of oscillation, then, as is 

 known, v is given by the maximum value of 



dx d / . ,.. t\ 2wa _ t 



i. e. 



2ira 



If m is the mass of the vibrating molecule, then ^mv 2 is its 

 store of luminous energy. We must introduce into the equa- 

 tion the maximum value of w, and not, as in the calculation of 

 intensity, the mean value during a vibration ; just as the 

 energy involved in the vibrations of a pendulum is deter- 

 mined by ^mv 2 , where again v denotes the value of the velocity 

 with which the pendulum passes through its position of equi- 

 librium. The total energy determined by the oscillatory 

 motion is gradually radiated, quite independently of the fact 

 that it is made up of potential and kinetic energy, at other 

 times than those when the particle is passing through its 

 position of equilibrium. 



If, further, G is the weight of the vibrating mass which is 

 contained in 1 gramme of the luminous body, 7 the accelera- 

 tion due to gravity, 430 the mechanical equivalent of heat, 

 then 



b 2 7 2 7 T 2 



We will put 7=10 metres, T=l/(ax 10 14 ), where axlO 14 

 denotes the number of vibrations in aether for the ray of light 

 in question ; then 



2x10x430 _E^ __1 E^ 



a 2 2 xir 2 x 10 28 d 2 Gxb 4-6 x 10 25 a 2 Gb ^ meire ^ ■ 



In reference to the weight G of the vibrating particle we 

 may make two extreme assumptions : — 



