82 FRAGMENTS OF SCIENCE 



believed to be the cause of light. But ISTewton's notion 

 has not held its ground, being entirely driven from the 

 field by the more wonderful and far more philosophical 

 notion that light, like sound, is a product of wave- 

 motion. 



The domain in which this motion of light is carried on 

 lies entirely beyond the reach of our senses. The waves 

 of light require a medium for their formation and propa- 

 gation; but we cannot see, or feel, or taste, or smell this 

 medium. How, then, has its existence been established? 

 By showing that, by the assumption of this wonderful in- 

 tangible etherj all the phenomena of optics are accounted 

 for, with a fulness, and clearness, and conclusiveness, 

 which leave no desire of the intellect unsatisfied. When 

 the law of gravitation first suggested itself to the mind 

 of Newton, what did he do? He set himself to examine 

 whether it accounted for all the facts. He determined the 

 courses of the planets; he calculated the rapidity of the 

 moon's fall toward the earth; he considered the precession 

 of the equinoxes, the ebb and flow of the tides, and found 

 all explained by the law of gravitation. He therefore re- 

 garded this law as established, and the verdict of science 

 subsequently confirmed his conclusion. On similar, and, if 

 possible, on stronger grounds, we found our belief in the 

 existence of the universal ether. It explains facts far more 

 various and complicated than those on which Newton based 

 his law. If a single phenomenon could be pointed out 

 which the ether is proved incompetent to explain, we 

 should have to give it up; but no such phenomenon has 

 ever been pointed out. It is, therefore, at least as certain 

 that space is filled with a medium, by means of which suns 

 and stars diffuse their radiant power, as that it is traversed 



