218 J. Trowbridge — Radiant and Electrical Energy. 



With this instrument we have no guide or indication of the 

 size of the electrical undulations which are transformed while 

 creating a stress in the dielectric which separates the two 

 plates of the condenser. I was led, therefore, to examine the 

 specific inductive capacity of well known insulators in order 

 to perceive if any relation exists between such inductive 

 capacities and the selective absorption of radiant energy which 

 these substances may exhibit. The first substance selected was 

 naturally paraffine. In order to examine its selective absorp- 

 tion a layer of it in the melted condition was contained be- 

 tween quartz plates. In order to keep it melted the plates 

 were imbedded in sand, an aperture being left for the passage 

 of light, and placed over a Bunsen burner. Light passing 

 through the paraffine was then examined by means of a spec- 

 troscope provided with quartz lenses and a quartz prism. It 

 was found that the paraffine transmitted the ultra violet rays 

 certainly as far as wave-length 3400. There was evidence that 

 absorption of the ultra violet rays began in the neighborhood 

 of this wave-length. Thin sheets of vulcanite were next 

 examined. These transmitted light through the extent of the 

 visible spectrum from the extreme limit of the red to the be- 

 ginning of the blue region of the solar spectrum. It was 

 opaque to the blue and the violet. 



The following table gives a comparison of the specific in- 

 ductive capacities of the substances examined and the range 

 of their selective absorption in the ultra violet. 



Specific Limit of 



Dielecric. inductive cap. transmission. 



Glass ' 3-243 about 3800 



Paraffine 2-32 about 3400 



Ebonite 3.15 opaque 



India rubber 3*24 opaque 



Quartz... 4'6 below 2000 



Iceland spar. .. 8 - 4 below 2000 



Boys has lately called attention to the remarkable insulating 

 qualities of quartz. 



From the above table we are apparently justified in drawing 

 the conclusion that the long waves of electrical radiation, the 

 existence of which has been shown by Hertz, behave like the 

 long waves of radiant energy which we term heat waves, and 

 perform work in the dielectric when transmitted in an alternat- 

 ing manner through it. The short waves of electrical energy 

 if they are analogous to the short waves of light are apparently 

 not absorbed by the dielectric when this dielectric approaches 

 perfection as a dielectric. The theory, therefore, that electri- 

 cal attraction may be due to extremely rapid vibrations of the 

 ether which cause attraction of bodies, much as a pith ball is 



