40 THE POPULAR SCIENCE MONTHLY. 



to science lias been the discovery that the figure which expressed 

 the velocity of light, also expressed the multiplier required to 

 change the measure of static or passive electricity into that of 

 dynamic or active electricity. The interpretation reasonably 

 affixed to this discovery is that, as light and the electric impulse 

 move approximately at the same rate through space, it is probable 

 that the undulations which convey them are undulations of the 

 same medium. And as induced electricity penetrates through 

 everything, or nearly everything, it follows that the ether through 

 which its undulations are propagated must pervade all space, 

 whether empty or full, whether occupied by opaque matter or 

 transparent matter, or by no matter at all. The attractive experi- 

 ments by which the late Prof. Hertz illustrated the electric vibra- 

 tions of the ether will only be alluded to by me, in order that I 

 may express the regret deeply and generally felt that death 

 should have terminated prematurely the scientific career which 

 had begun with such brilliant promise and such fruitful achieve- 

 ments. But the mystery of the ether, though it has been made 

 more fascinating by these discoveries, remains even more inscru- 

 table than before. Of this all-pervading entity we know abso- 

 lutely nothing except this one fact, that it can be made to undu- 

 late. Whether, outside the influence of matter on the motion of 

 its waves, ether has any effect on matter or matter upon it, is 

 absolutely unknown. And even its solitary function of undulat- 

 ing ether performs in an abnormal fashion which has caused 

 infinite perplexity. All fluids that we know transmit any blow 

 they have received by waves which undulate backward and for- 

 ward in the path of their own advance. The ether undulates 

 athwart the path of the wave's advance. The genius of Lord 

 Kelvin has recently discovered what he terms a labile state of 

 equilibrium, in which a fluid that is infinite in its extent may 

 exist, and may undulate in this eccentric fashion without outra- 

 ging the laws of mathematics. I am no mathematician, and I can 

 not judge whether this reconciliation of the action of the ether 

 with mechanical law is to be looked upon as a permanent solu- 

 tion of the question, or is only what diplomatists call a modus 

 Vivendi. In any case it leaves our knowledge of the ether in a 

 very rudimentary condition. It has no known qualities except 

 one, and that quality is in the highest degree anomalous and 

 inscrutable. The extended conception which enables us to recog- 

 nize ethereal waves in the vibrations of electricity has added in- 

 finite attraction to the study of those waves, but it carries its own 

 difficulties with it. It is not easy to fit in the theory of electrical 

 ether waves with the phenomena of positive and negative elec- 

 tricity ; and as to the true significance and cause of those counter- 

 acting and complementary forces, to which we give the provi- 



