82 M. E. Edlund on the Nature of Electricity. 



as well as dynamic^ can be explained with the aid of a single 

 fluidj which in all probability is no other than the sether*. 

 We assume the existence of a subtile, in the highest degree 



* We take the hberty of borrowing, from the address dehvered by Baron 

 F. deWrede, in 1847, on retiring from the Presidentship of the Royal 

 Academy of Sciences, the following hnes on the importance of the aether: — 

 " One can no more admit that a substance filhng infinite space, and exhi- 

 biting properties so peculiar and remarkable as those which we must neces- 

 sarily attribute to the aether, has been destined by Providence solely to 

 propagate light, than we can suppose that the ah exists exclusively for the 

 propagation of sound. The slightness of the density of the aether is proved 

 by the total inappreciability of its resistance to the planets, which appear 

 to move in it without impediment. The comets, on the contrary, the te- 

 nuity of which is singularly extreme, and which move with some of the 

 greatest velocities in certain parts of their orbits, seem to experience a sen- 

 sible resistance from the aether. If this fact be verified, the existence of 

 the aether as matter endowed with inertia will be found established by a 

 second method. On the other hand, the prodigious rapidity with which 

 hght is propagated shows us that the aethereal matter must possess extra- 

 ordinary elasticity in comparison with its density. Of all the material sub- 

 stances within the limits of our experience, iron is the most elastic, and 

 hydrogen (which has only about one fourteenth of the w'eight of atmo- 

 spheric air) the lightest. Now a substance equal in density to hydrogen 

 rarefied to about 1 millim. pressure, and as elastic as iron, would propagate 

 sound (or any other vibratory motion) with a velocity of 8000 m^'riametres 

 (49,7 lOi miles) in a second. Immense as this velocitj^ is, it constitutes 

 only about one fifth of that of light ; and the modulus of elasticity of the 

 aether, expressed in terms of the length, must consequently be about 25 

 times that of the hypothetic substance here taken for compai'ison. If we 

 regard the aether as a gas, and imagine the possibility of a vacuum in it, the 

 velocity with which the aether would rush into that vacuum would amount 

 to 64,000 myriametres in a second ; and estimating its density at the very 

 lowest, its mechanical effects might, with that velocity, become singularly 

 violent. It is therefore a thing in itself very probable that the aether plays 

 one of the most important parts in almost all natural phenomena." 



We permit ourselves also to quote the following from the end of Iiame''s 

 celebrated Legons surla theorie mathematique de V elasticite des corps solides 

 (Paris, 1852) :— 



" The existence of the aethereal fluid is incontestably demonstrated by the 

 propagation of light in the planetary spaces, by the explanation so simple, 

 so complete, of the phenomena of diffraction in the theory of undulations ; 

 and, as we have seen, the laws of double refraction prove with no less cer- 

 tainty that the aether exists in all transparent media. Ponderable matter 

 is therefore not alone in the universe; its particles float, in a manner, in 

 the midst of a fluid. If that fluid is not the sole cause of all the facts ob- 

 servable, it must at least modify them, propagate them, complicate their 

 laws. It is, then, impossible to ai-rive at a rational and complete explana- 

 tion of the phenomena of physical nature without interposing this agent, 

 whose presence is inevitable. It cannot be doubted that that interposition, 

 wisely guided, will discover the secret, or the true cause, of the effects which 

 are attributed to caloric, to electricity, to magnetism, to universal attraction, 

 to cohesion, to chemical attractions; for all these mysterious and incom- 

 prehensible beings are, in the main, merel}' hypotheses of coordination, 

 doubtless useful in our present ignorance, but eventually to be dethroned 

 by the progress of true science." 



