THE LAW OF CONTINUITY. 33 



doubts that matter can act where it is not. What light have recent 

 researches shed upon this interesting question, heretofore little more 

 than metaphysical ? 



The solar atmosphere has been found to extend to more than half 

 a radius beyond its surface; at the top of its corona, high above the 

 hydrogen, there are vast masses of a gas which emits a simple, green 

 ray, not corresponding with that of any known substance. In auro- 

 ral displays on earth, in the uppermost regions of our atmosphere, the 

 same simple ray has been detected; whence it has been supposed that 

 atmospheres are not restrictedly planetary nor solar, but continuous 

 and cosmical; and that it may be a gas indefinitely rarefied that con- 

 veys tQ us through the depths of space not only light-motion, but the 

 yet more inappreciable tremors of electricity and gravitation. 



The ordinary definitions of the interstellar ether are open to the 

 objections urged by Mill, because of a dread there seems to be abroad 

 of ascribing materiality to it ; while its infinitesimal materiality is not 

 only within the bounds of possibility, but well agrees with the facts. 

 All motion takes time ; light has a measurable velocity ; chemical ac- 

 tion of the most violent kind and even explosions are not instantane- 

 ous. Were it otherwise, the hypothesis of no medium or of an imma- 

 terial one might be entertained. Now, the decidedness in amount of 

 a body's weight as a mass, or in its particles, has no necessary connec- 

 tion with its efficiency as a medium of motion. Just the reverse: we 

 find that as matter is smaller and lighter in its ultimate parts or gross 

 masses, the more rapidly can it communicate motion, and the greater 

 is its capacity for motion. It is a familiar fact that, in the use 

 of machinery, a small wheel can, proportionately to its weight, con- 

 tain and transmit more motion than a large one, the plain reason 

 of which is that it can be driven at a higher peripheral speed, its 

 smaller bulk causing less centrifugal strain at the axis than if it were 

 larger. 



Sound travels nearly four times faster in hydrogen than in air, 

 and in quickness of elastic recoil it is, when compressed, preferable to 

 air in the same degree. Its extraordinary chemical energy, far tran- 

 scending that of denser gases, is a fact of parallel bearing. 



If we can imagine a gas as much thinner than hydrogen as the 

 square of light's velocity exceeds the speed of sound in hydrogen 

 (about 4,000 feet a second), we have a reasonable presentation of 

 what the luminous medium may be its marvelous tenuity being 

 vastly more than compensated by the mobility of its molecules. 

 And, therefore, the most subtile aeriform fluid conceivable is of enor- 

 mously more utility in propagating impulses from star to star than 

 solid steel would be. The ether of space perhaps sustains some such 

 relation to a gas as a gas does to a liquid ; and the current disputes 

 as to the materiality or immateriality of a cosmic medium recall very 

 suggestively the days, not very distant, when wise men doubted the 



VOL. XII. 3 



