THE NEW THEORY OF MATTER. 497 



merit. I suppose that if at that period the average man of science had 

 been asked to sketch his general conception of the physical universe, 

 he would probably have said that it essentially consisted of various 

 sorts of ponderable matter, scattered in different combinations through 

 space, exhibiting most varied aspects under the influence of chemical 

 affinity and temperature, but through every metamorphosis obedient 

 to the laws of motion, always retaining its mass unchanged, and exer- 

 cising at all distances a force of attraction on other material masses, 

 according to a simple law. To this ponderable matter he would (in 

 spite of Eumford) have probably added the so-called ' imponderable ' 

 heat, then often ranked among the elements; together with the two 

 ' electrical fluids,' and the corpuscular emanations supposed to consti- 

 tute light. 



In the universe as thus conceived, the most important forms of 

 action between its constituents was action at a distance; the principle 

 of the conservation of energy was, in any general form, undreamed of; 

 electricity and magnetism, though already the subjects of important 

 investigation, played no great part in the whole of things; nor was a 

 diffused ether required to complete the machinery of the universe. 



Within a few months, however, of the date assigned for these de- 

 liverances of our hypothetical physicist, came an addition to this gen- 

 eral conception of the world, destined profoundly to modify it. About 

 a hundred years ago Young opened, or reopened, the great controversy 

 which finally established the undulatory theory of light, and with it 

 a belief in an interstellar medium by which undulations could be con- 

 veyed. But this discovery involved much more than the substitution 

 of a theory of light which was consistent with the facts, for one which 

 was not; since here was the first authentic introduction* into the sci- 

 entific world picture of a new and prodigious constituent — a constitu- 

 ent which has altered, and is still altering, the whole balance (so to 

 speak) of the composition. Unending space, thinly strewn with suns 

 and satellites, made or in the making, supplied sufficient material for 

 the mechanism of the heavens as conceived by Laplace. Unending 

 space filled with a continuous medium was a very different affair, and 

 gave promise of strange developments. It could not be supposed that 

 the ether, if its reality were once admitted, existed only to convey 

 through interstellar regions the vibrations which happen to stimulate 

 the optic nerve of man. Invented originally to fulfil this function, 

 to this it could never be confined. And accordingly, as every one now 

 knows, things which, from the point of view of sense perception, are 

 as distinct as light and radiant heat; and things to which sense per- 



* The hypothesis of an ether was, of course, not new. But before Young 

 and Fresnel it can not be said to have been established. 



vol. lxv. — 32. 



