THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOUKNAL OF SCIENCE. 



♦ 



[FIFTH SERIES.] 



APRIL 1879. 



XXXVIII. The Existence of the Luminiferous Ether. By 

 Ernest H. Cook, B.Sc, A.P.C.S., Lecturer on Physics at 

 the Bristol Trade and Mining School*. 



THE enormous velocity with which the motion producing 

 light is propagated through space induced the authors of 

 the undulatory theory to seek about for some medium capable 

 of transmitting the vibratory movement. Applying the known 

 laws of the propagation of sound, which is also a vibratory 

 movement, this medium must possess enormously high elas- 

 ticity and extremely small density. Such a medium is the 

 luminiferous ether. This substance fills all space, and is im- 

 prisoned between the atoms of all bodies. The vibrations of 

 the atoms of luminous bodies are communicated to the ether, 

 and by it transmitted in all directions. Each particle of the 

 ether makes a small movement to and fro ; but the whole mass 

 is thrown into wave-like motions. The elasticity or density 

 of the ether in free space is different from that of the same 

 ether when imprisoned by the molecules of material bodies. 

 Thus in a refracting body like glass, the elasticity of the ether 

 is less (or its density is greater) than in air, and the elasticity 

 in air is less than in a vacuum. We therefore find that the 

 velocity of light in glass is less than it is in air, and is less in 

 air than it is in a vacuum. Moreover in most crystalline sub- 

 stances the elasticity of the ether is different in different 

 planes ; and we find that light traverses such substances with 

 different velocities in different directions. The explanation 

 * Communicated by the Author. 

 Phil. Mag. S. 5. Vol. 7. No. 43. April 1879. T 



