LIGHT AND ITS ARTIFICIAL PRODUCTION. ^ 



By Dr. O. Lummer. 



Part I. 



HISTORICAL INTRODUCTION. 



Of the five senses of man that of sight is without doubt the one 

 which first makes known to us the intimate relationship between inter- 

 nal self and the external world. 



If we close our eyes, the magnificent colors and the manifold forms of 

 nature with their lights and shadows all vanish. Everything is wrapped 

 in dreary impenetrable darkness; we have lost the safe guidance of 

 sight, and left to the uncertain guidance of the sense of touch, we grope 

 around in this darkness. There is no light for us except where there 

 is sight. The Greek philosophers were wrong in their belief that light 

 was a something emanating from the human eye, which returning from 

 outside objects rendered these visible. The evidence points to a some- 

 thing emanating from visible objects which, penetrating to the retina, 

 evokes in the brain the sensations of light and darkness, color and luster. 

 Newton and his school believed that the something emitted by lumi- 

 nous bodies consisted of minute material particles (corpuscles). 



This theory was, however, supplanted by the wave theory of Huygens, 

 according to which that something which is emitted by luminous bodies is 

 not a stream of particles, but a wave-like motion of the " ether," which 

 must be considered as permeating all forms of matter from the lightest 

 gas to the densest metal. Infinite space is an ocean of ether in which 

 all natural phenomena take place. Unresisted by friction, the planets 

 glide swiftly through it. But just as a stone dropped into water pro- 

 duces ripples in its smooth surface, just as a vibrating tuning fork com- 

 municates its vibrations to the air, so does a source of light set in 

 motion the ether, Sound and light, pitch and color, exactly corre- 

 spond to one another. A source of light j^roduces light waves in the 

 ether just as a tuning fork produces sound waves in the air. The sound 

 waves penetrating to the auditory nerves through the drum of the ear 

 produce in the brain the sensation of sound, and similarly the ether 

 waves, reaching the retina through the lens, produce the sensations of 



■ Illustrated lecture by Dr. 0. Lummer, delivered February 5, 1897, before the 

 Berlin Polytechnical Society. Translated from the German. 



sm97 18 273 



