( 421 ) 



time, as lias also hoen llie rule implied in our formulae, that these 

 densities are inversely pi'oportional to the cube of the velocity of 

 propaoation r. It must further be noticed that, if the medium L is 

 aether, the density of the energy of the radiation becomes 



8 jt k^n 

 c 

 This agrees with the meaning we have originally attached to the 

 coefficient k (§ 11). 



^ 19. There is one point in the foregoing considerations that may 

 at first sight seem strange, viz. that the intensity of the electromotive 

 forces we have imagined should depend on the magnitude of the 

 elements of volume s. It must be kept in mind however, that these 

 forces have no real existence, and that we do not pretend to have 

 found something concerning the causes by which the phenomena are 

 produced. That the magnitude of the electromotive forces must be 

 taken inversely proportional to the square root of the volume of s 

 is simply a consequence of our assumption that the force has the 

 same phase in all points of such an element. For a given amplitude 

 of the electromotive force, the radiation would therefore be propor- 

 tional to s% and we had to make such assumptions concerning that 

 amplitude, that the radiation became proportional to s itself. 



In connection with these remarks it must be observed that we 

 have no reasons for ascribing to the dimensions of the elements 

 of volume some particulai' value. These dimensions are indifferent as 

 long as we consider only the radiation at finite distances and the 

 transfer of energy between neighbouring molecules lies outside the 

 theory I have here developed. 



PhysiologSf. — "On the ability of distingidshlng intensities of tones*\ 

 By Prof. H. Zwaardemaker. (Report of a research made by 

 A. Deenik.) 



The "Unterschiedsschwelle" for impulsive sounds (dropping bullets 

 and hammers) has been studied frequently and many-sidedly, but 

 regarding the "Unterschiedsschwelle" for intensities of tone we have 

 had at our disposal till now only some information communicated 

 by M. WiEN in his thesis. 



M. WiEN found the value of the "Unterschiedsschwelle" for the 

 three tones, to which he limited his investigation to be as follows : 

 for a average 22.5"/, (with 18.2 and 27 for extremes) for e' 17.67o 



29 



Proceedings Royal Acad. Amsteidam. Vol. VIII. 



