510 PRESENT FUNDAMENTAL CONCEPTIONS OF PHYSICS. 



existence, which were believed to combine in the colorless ray to a col- 

 orless substance. Besides this, a peculiar caloric had to be assumed. 

 The absorption of light could be considered only as a union of the ca- 

 loric with substances by which the former lost its essential property, 

 namely, its illuminating power. Thus many phenomena of light could 

 not be explained by the theory of the emission of light, even with the 

 assistance of new auxiliary hypotheses. How clearly does the undula- 

 tory theory explain, not only all the light phenomena, but also those of 

 heat and chemically acting radiation ! By the application of the prop- 

 osition relative to the conservation of energy, the transformation of one 

 kind of ray into another, as well as the absorption of rays, is easily 

 comprehended. 



By applying the undulatory theory to both heat and light, a common 

 basis has been gained for them ; the rays of heat and light are even iden- 

 tical. The undulatory theory of the aether being formed according to 

 the demonstrated undulatory theory of acoustics, it shows by analogy, 

 as indicated above, what the conception of the transmission of kinetic 

 energy in acoustics is. First, in relation to the calling forth of tones, 

 the mechanical work of bowing or striking the resounding instru- 

 ment is changed into the kinetic energy of the vibrating motion of 

 molecules. From the resounding body the kinetic energy passes over 

 to the sound transmitter in form of progressing longitudinal waves, and 

 from the sound transmitter by means of the vibratory parts of the ear 

 to the extreme ends of the auditory nerves, whereby finally the per- 

 ception of sound is produced. If the sound waves however strike 

 accordant bodies, the latter get into resonance in consequence of the 

 transmission of kinetic energy. In optics a similar calling forth of 

 tones or colors in suitably constituted bodies by colored rays falling 

 upon them is known ; these phenomena are called fluorescence and phos- 

 phorescence. 



We have observed that the theories of heat light and sound have been 

 reduced to one of undulation. And since the latter is deduced from 

 mathematical mechanics, these theories have theoretical mechanics as 

 their basis, and, above all, the fundamental principle of the conservation 

 of energy. The many relations existing between electrical, optical, and 

 thermal phenomena, continually more and more discovered and displayed 

 since the wider development Of the mechanical theory of heat, are natur- 

 ally calculated to arouse the efforts of natural philosophers to explain the 

 fundamental phenomena of electricity also from some motion of material 

 molecules or aether atoms, the many counter actions between the ther- 

 mal, optical, and electrical phenomena having rendered untenable the 

 hypothesis of electric fluids, or electric substances. 



Up to the present time there have been two leading hypotheses by which 

 the theory of electric phenomena was to be connected with the sether 

 theory of optics and heat. One of these hypotheses maintains that there 

 are opposite rotatory motions of the material molecules or aether atoms 



