92 SCIENTIFIC THOUGHT. 



mechanical notion that is put before us by Fresnel and 

 his followers, to take up the so-called electro-magnetic 

 theory of light in the way it has been taken up by several 

 writers of late." 



But whilst, no doubt, the train of reasoning started by 

 Maxwell, and developed by his followers, has somewhat 

 destroyed the simplicity and directness which the older 

 vibratory theory of light and the kinetic theory of gases 

 had brought into our mechanical views of natural 

 phenomena, the subsequent experimental proof of the 

 existence of electric waves by Hertz has done much 

 popularly to strengthen that view. The discovery of 

 other kinds of rays, by Lenard, Eontgen, and others, has 

 likewise tended in the same direction, though their exact 

 nature is still a subject of much conjecture. 



Nor can it be denied that the practical usefulness 

 also of these lately discovered forms of radiation has 

 tended in the same direction ; as has, all through the 

 last thirty years, the enormous development of electrical 

 industry in its many branches. Up to the beginning 

 of the nineteenth century the principal electric and 

 magnetic phenomena known were what we term stat- 

 ical ; the study of these centred in the conception of 

 electric and magnetic charges concentrated on or in 

 conductors and acting at a distance. The practical 

 interest was limited to mariners' compasses and light- 

 ning-conductors. The discovery of the galvanic current, 

 and still more its applications by Davy to the decom- 

 position of the most refractory chemical compounds, 

 introduced an entirely new class of phenomena. Con- 

 tinental science, in Coulomb, Ampere, and Weber, first 



