ADDRESS. 9 



extension. One of the most brilliant of the services which Professor 

 Maxwell has lendered to science has 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 discoveiy 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 experiments 

 by which the late Professor Herz illustrated the electric vibrations 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 pre- 

 maturely the scientific career which had begun with such brilliant promise 

 and such fruitful achievements. But the mystery of the ether, though it 

 has been made more fascinating by these discoveries, remains even more 

 inscrutable than before. Of this all-pervading entity we know absolutely 

 nothing except this one fact, that it can be made to undulate. Whether,, 

 outside the influence of matter on the motion of its Avaves, ether has any 

 effect on matter or matter upon it, is absolutely unknown. And even its 

 solitary function of undulating, 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 backwards and 

 forwards 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 outraging the laws of mathematics. I am no mathema- 

 tician, and I cannot judge whether this reconciliation of the action of the 

 ether with mechanical law is to be looked upon as a permanent solution 

 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 recognise ethereal waves in the vibrations of electricity has 

 added infinite 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 electricity, and as to 

 the true significance and cause of those counteracting and complementary 

 forces, to which we give the provisional names of negative and positive, 

 we know about as much now as Franklin knew a century and a half ago. 

 I have selected the elementary atoms and the ether as two instances. 

 of the obscurity that still hangs over problems which the highest scientific 

 intellects have been investigating for several generations. A more 



