On Electric Energy-Distribution* 357 



We think, then, that our experiments prove that von Helm- 

 holtz was correct in stating that the siren produces two 

 objective notes the frequencies of which are respectively equal 

 to the sum and difference of the frequencies of the funda- 

 mentals, and that our observations are also more or less 

 opposed to the theories by which Konig, Appun, and Terquem 

 have sought to account for the production of these notes. 



We believe that the method we have devised is capable of 

 greater seDsitiveness. It can be extended by employing 

 forks of different pitches, and it is quite possible that less 

 massive forks may enable us to detect effects which have 

 hitherto escaped us. We therefore refrain from any wide 

 generalizations until a wider foundation of experiment has 

 been laid. 



P.S. — Since the above was written Prof. S. P. Thompson has 

 drawn our attention to a paper by 0. Lummer, published in 1886 

 (Verli. phys. Gesell. Berlin, 1886, No. 9, p. 66), which had escaped 

 our notice, as it is not abstracted in the Beiblatter. Herr Lummer 

 obtained evidence of the objective character of the summation-tone 

 by means of the microphone. 



XXXIV. Energy Movements in the Medium separating 

 Electrified or Gravitating Particles. By H. N. Allen, 

 University of Nebraska* Lincoln. Neb. 



1. Ij^ABADAY and Maxwell have shown that it is possible 

 J- to look on the potential energy of electric separation 

 as residing in the surrounding dielectric, and that each of 

 the cells, bounded by the walls of a tube of force and two 

 neighbouring equipotential surfaces, can be looked upon as 

 containing a certain definite amount of energy. 



This energy-distribution is not in general permanent, and 

 can only be regarded as a step towards some simpler ar- 

 rangement. Thus a positive and a negative electrified body 

 suspended in space, and acted on only by the electrical 

 forces between them, are never in equilibrium until they are 

 in actual contact. The energy-distribution in the dielectric 

 changes constantly as they approach. Poynting has shown f 

 how energy is transferred from one point to another in an 

 electromagnetic field ; and we are quite accustomed to think 

 of energy as flowing from dynamo to motor through the 

 aether, or from primary to secondary in an alternating-current 

 transformer. 



In the foliowing pages an attempt is made to deduce a few 



* Communicated hy the Physical Society : read March 8, 1895. 

 t Phil. Trans. 1884, Pt. II. p. 343. 



Phil. Mag. S. 5. Yol. 39. No. 239. April 1895. 2 B 



