HEINRICH HERTZ 365 



fact of which Hertz brought as complete a proof as possible 

 in the case of the oscillator. 



We see that Maxwell's equations exhibit the behaviour 

 of the electric and magnetic lines of force, their form and 

 their motions, even in very complicated circumstances. 

 These lines of force, which, when they are not closed in 

 upon themselves (as are the magnetic lines always, the elec- 

 tric lines in waves), are linked at one end to positive, at the 

 other to negative electricity, afford accurate and exhaustive 

 pictures of states of space - of the ether - which are in- 

 separably connected once and for all with the two kinds of 

 electricity. For this reason Maxwell's equations appeared 

 actually as the equations exhibiting the behaviour of ether, as 

 far as that was known at the time. 



This necessarily suggested that the behaviour of ether 

 could be compared by means of these equations with the 

 behaviour of matter. We know that in liquids and gases 

 propagation of waves also occurs - these are known as sound 

 waves - and that liquids and gases are also able to transmit 

 pressure forces which likewise require time for their propaga- 

 tion. In order to compare the ether with a liquid, for 

 example, it was a matter of comparing Maxwell's equations 

 with the equations of hydro-dynamics, and seeing whether 

 complete agreement exists when, for example, the electric 

 forces are interpreted as displacements in the ether, or 

 whether other interpretations also lead to agreement. 



Mathematical investigations made for this purpose have 

 all led to the result that striking similarity exists between 

 ether and liquids or gases (or also solid bodies) in certain 

 respects, but that complete agreement is wanting.^ We can 



1 Particularly the profound investigations of Carl Anton Bjerknes, 

 which were begun before the appearance of Maxwell's work, and were 

 also not connected with it, 'On Hydrodynamic Forces at a Distance' 

 werean important contribution to a clearer understanding of the mechanics 

 of the ether. They appeared in English, in lectures given in 1905 at 

 Columbia University by his son V. F. K. Bjerknes, and published under 

 the title Fields of Force, London and New York, 1906. 



