HEINRICH HERTZ 363 



Thus waves were found in the ether, exactly similar to 

 light waves in every respect excepting length. While the 

 waves of visible light, measured by Fraunhofer and Fresnel, 

 were of lengths measured in ten-thousandths of a milli- 

 metre. Hertz had obtained invisible light waves of a length, 

 measured in feet, or when he made his oscillator still smaller, 

 in inches; and he was able to investigate their electric and 

 magnetic force in detail. No further doubt could exist that 

 the waves of visible light are also such waves of electric and 

 magnetic force, although these forces, in view of the small- 

 ness of the waves, cannot be detected by ordinary means. 

 A particular proof of the fact that the waves of electric oscil- 

 lators have all the properties to be expected in long light 

 waves, was given by Hertz in his well-known concave 

 mirror experiment. He here obtained rays of electric 

 force analogous to the rays from a searchlight, and he could 

 demonstrate their refraction by a prism and measure it, 

 everything being again found to agree with Maxwell's equa- 

 tions. In this way, not only was the electro-magnetic 

 nature of light waves and of all phenomena of light proved 

 and rendered perfectly clear, but it was also shown that all 

 known electric and magnetic phenomena, including those of 

 light, are processes of the same type taking place in one and 

 the same ether, and only differing in their spatial arrange- 

 ment, but in every case following Maxwell's equations. 

 Maxwell's equations were now the summary of everything 

 known up to that time concerning the ether. 



Since then, ether waves of every length have become 

 known, and can be generated. The waves measured in kilo- 

 metres or centimetres and proceeding from electrical oscil- 

 lators, link up, in a long scale of wave-lengths, with the 

 longest infra-red waves which proceed from hot bodies, and 

 so with the waves of the visible spectrum from red to violet; 

 these are followed by the still shorter and again invisible 

 ultra-violet, which are contained in the light of electric 



