J. Trowbridge — Radiant and Electrical Energy. 217 



Aet. XXIX. — Radiant Energy and Electrical Energy • by 

 John Trowbridge. 



The relations between radiant energy and electrical energy 

 are daily becoming more important, and the experiments of 

 Hertz on Electrical Rays lead one to ask whether the doctrine 

 of the conservation of energy can guide us in answer to the 

 question, what are the transformations of energy in a dielectric 

 submitted to rapidly alternating electrical stress ? 



Hertz has also shown that ultra violet waves of light exercise a 

 marked influence upon the striking distance of the electric spark. 

 E. Wiedemann attributes this effect to a selective absorption 

 of the metals between which the spark is passed. Thus plati- 

 num terminals show the effect in a more marked degree than 

 the terminals of other metals, and it is well known that platinum 

 exercises a marked selective absorption for violet rays. This 

 explanation of the phenomenon observed by Hertz may how- 

 ever be only a partial explanation. The question still remains, 

 do ultra violet rays exert any effect upon a dielectric which 

 becomes manifest in changes of electrical stress ? Or, to put the 

 question in another form, are the shorter waves of electrical 

 energy passing between the plates of a condenser, separated by 

 various dielectrics, absorbed by the dielectric, or is this the case 

 for the long waves only ? It is well known that a dielectric is 

 under stress when submitted to rapidly alternating electrical 

 charges. Under the supposition that an electrical wave or 

 disturbance in the ether carries heat and light waves ; or that 

 there is a close correspondence between the phenomena of 

 light and heat waves and electrical waves, we are led to ask 

 if there are not transformations similar to those Alexander 

 Graham Bell has shown to exist in substances submitted to the 

 action of rapidly interrupted waves of energy in the form of 

 heat. The Radiophone shows that the long waves of energy 

 become absorbed in passing through various substances. The 

 transformation of energy is shown by a musical note which is 

 that of the wheel employed to interrupt the beam of light 

 which falls upon the substance under examination. The effect 

 is evidently due to the long waves of energy which we call 

 heat. The effect might have been anticipated ; for Balfour 

 Stewart had shown that a body subjected to changes of tem- 

 perature undergoes a change not only at its surfaces, but 

 also throughout its interior. The rapidity of these changes, 

 however, had not been suspected until the invention of the 

 Radiophone. 



In the case of the Dolbear telephone, electrical oscillations 

 are transmitted from one plate of an air-condenser to another. 



