INTRA-ATOMIC ENERGY. 27T 



the matter of the sun "and the phmets that surround It throughout a 

 space equal to that which separates us from the nearest fixed stars, a 

 cubic myriameter of such matter thus diffused into a gaseous state 

 would scarceh" weigh the millionth of a milligram, and would con- 

 sequently be imponderable in our balances. A gas of such tenuity, 

 representing perhaps the primitive state of our nebula, would be 

 a quadrillion times less dense than the vacuum carried to the mil- 

 lionth of an atmosphere in a Crookes tube. 



Unhappily the constitution of the ether can not be compared in any 

 way with that of a gas. Gases are' very compressible, while ether can 

 not be notably compressed. If it were, it could not transmit almost 

 instantaneously the vibrations of light. 



It is only in fluids theoretically perfect, or, better yet, in solids, that 

 we can find distant analogies with the ether; but we nmst then imagine 

 a substance having very singular ])roperties. It must have a rigidity 

 surpassing that of steel, for if it did not possess that it would not 

 transmit luminous vibrations at a speed of 300,000 kilometers per 

 second. The most illustrious of our modern ph3^sicists, Lord Kelvin, 

 considers ether as "an elastic solid filling all space." 



The elastic solid that forms the ether has very strange properties for 

 a solid, properties which we find in no other. Its extreme rigidity 

 must be associated with an extraordinarily low density — that is to say, 

 so low that its friction is una])le to retard the motion of the stars in 

 space. Hein has calculated that if the density of the ether were only 

 a million times less than that of the air of a Crookes tul^e it would 

 produce a secular alteration of half a second in the average motion of 

 the moon. Such a medium, in spite of its greath' reduced density, 

 would soon remove the atmosphere from the earth. It has been cal- 

 culated that if it had the properties that we attribute to a gas it would 

 acquire by its impact with the surface of planets deprived of atmos- 

 phere, like the moon, a temperature of 38,000'^. Finally we reach 

 the idea that the ether is a solid without densit}" or weight, unintelli- 

 gi])le as such a proposition ma}^ seem. 



In order to explain the phenomena observed we must admit tliat in 

 this subtance, more rigid than steel, bodies move freely, and we may 

 produce in it, by setting on fire any substance whatever, those pro- 

 digiousl}' rapid vibrations called light — vibrations of sucli A'elocity 

 that if we compare th(nn with the speed of a cannon ])all the latter 

 seems at rest. With a piec(^ of glass cut in a certain manner Ave can 

 deflect the luminiferous ether from its course and separate its A-i))ra- 

 tions. It is an agent that we encounter everywhere, that Ave set into 

 vibration and deflect at Avill, hut wliich Ave can never seize. 



That which is still more astonishing is the magnitude ol' tiie forces 

 which Ihe ether is al)k^ to transmit. An electromagnet must act across 

 a vacuum by the intermediation of the ether. Now, as Lord Kelvin 



