356 A SHORT HISTORY OF SCIENCE 



I have deduced the relation between the statical and dynamical 

 measures of electricity, and have shown by a comparison of the 

 electro-magnetic experiments of Kohlrausch and Weber with the veloc- 

 ity of light as found by Fizeau, that the elasticity of the magnetic 

 medium in air is the same as that of the luminiferous medium, if these 

 two coexistent, coextensive and equally elastic media are not rather 

 one medium. . . . We can scarcely avoid the inference that light 

 consists in the transverse undulations of the same medium which is 

 the cause of electric and magnetic phenomena. Maxwell. 



We must not listen to any suggestion that we may look upon the 

 luminiferous ether as an ideal way of putting the thing. A real matter 

 between us and the remoter stars I believe there is, and that light 

 consists of real motions of that matter, motions just such as are 

 described by Fresnel and Young, motions in the way of transverse 

 vibrations. 



Kelvin, Baltimore lecture. 



Hertz, a pupil of Helmholtz, first proved in 1887 the existence 

 of those undulations which now bear his name, showing also 

 that these travel with the rapidity of light, and that they are, 

 like light and heat waves, susceptible of reflection, refraction, 

 and polarization, and until he measured their length and velocity, 

 no great progress was made in verifying those relations experi- 

 mentally. Such more recent applications of Hertz's ideas as 

 radio-telegraphy and radio-telephony testify to their immense 

 practical as well as theoretical importance. 



With the establishment of the electromagnetic theory of light, 

 what we may call the undulatory series became complete. Sound 

 had long been known to be due to waves or "undulations " and 

 the wave theory of heat and of light was accepted, so that it had 

 only remained to prove the existence of electrical and magnetic 

 undulations, and to show that such waves moved with the 

 velocity and other characteristics of light. This it was which 

 was done mathematically by Maxwell and experimentally by Hertz. 



The velocity of propagation of an electro-magnetic disturbance 

 in air ... does not differ more from the velocity of light in air . . 

 than the several calculated values of these quantities differ among 

 each other. Maxwell. 



