THE STORY OF NINETEENTH-CENTURY SCIENCE 



quivers that run through the jelly when it is shaken, 

 and the elastic tension under which it is placed when its 

 mass is twisted about, furnish some analogy to the quiv- 

 ers and strains in the ether, which are held to constitute 

 radiant energy, magnetism, and electricity. 



The great physicists of the day being at one regarding 

 the existence- of this all-pervading ether, it would be a 

 manifest presumption for any one standing without the 

 pale to challenge so firmly rooted a belief. And, in- 

 deed, in any event, there seems little ground on which 

 to base such a challenge. Yet it may not be altogether 

 amiss to reflect that the physicist of to-day is no more 

 certain of his ether than was his predecessor of the 

 eighteenth century of the existence of certain alleged 

 substances which he called phlogiston, caloric, corpuscles 

 of light, and magnetic and electric fluids. It would be 

 but the repetition of history should it chance that be- 

 fore the close of another century the ether should have 

 taken its place along with these discarded creations of 

 the scientific imagination of earlier generations. The 

 philosopher of to-day feels very sure that an ether ex- 

 ists ; but when he says there is " no doubt " of its exist- 

 ence he speaks incautiously, and steps beyond the bounds 

 of demonstration. He does not know that action cannot 

 take place at a distance ; he does not know that empty 

 space itself may not perform the functions which he 

 ascribes to his space-filling ether. 



ii 



Meantime, however^ the ether, be it substance or be 

 it only dream-stuff, is serving an admirable purpose in 

 furnishing a fulcrum for modern physics. Not alone 



