1901.] on Electric Waves. 495 



transparent to electric waves ; it is almost quite opaque to the much 

 shorter waves of dark heat ; it is again transparent to the still 

 shorter waves of visible light ; and it is again opaque to the shorter 

 ultra-violet rays, and intensely opaque to the shortest waves of all, 

 the X-rays. 



The phenomenon of polarisation was next considered. From the 

 way in which the waves are produced, we should expect to find that 

 they are polarised at their source. It was shown how this might 

 be tested by means of a frame over which a series of parallel copper 

 wires were stretched. If the frame were held in the path of the 

 waves, with the wires parallel to the spark, the grid would be opaque ; 

 if it were held with the wires perpendicular to the spark, the grid 

 would be transparent. The experiment was tried, and the result fell 

 out as expected. The grid behaved with respect to the electric 

 waves, just as the analyser in a polariscope behaves with respect to 

 a beam of plane polarised light. 



The lecturer then called attention to the great variety of ether 

 waves with which we are now acquainted, and having pointed out 

 the position which each group occupies in the scale, said in conclu- 

 sion : " Thus we come to realise that the various forms of energy to 

 which, in common language, we give the names of electricity, mag- 

 netism, heat, light, chemical action, are all transmitted through 

 space in the form of waves or vibrations of the ether ; and that these 

 vibrations are all essentially of the same kind, being distinguished 

 from one another only by their wave-length. They produce widely 

 different effects, when they strike upon our different senses ; but 

 considered in themselves they are only, so to say, notes of different 

 pitch in the great scale of radiant energy which I have imperfectly 

 attempted to sketch. This large and comprehensive view of radiant 

 energy is one of the most notable results achieved by the great 

 scientific men of the century that has just passed away. And the 

 work that remains to be done by the coming generation, the great 

 scientific men of the twentieth century, is to explore more thoroughly 

 the properties of these ethereal waves, to fill up the gaps that still 

 exist in the scale, and perhaps to reveal to the world the intrinsic 

 constitution of the ether itself, that mystery of mysteries which 

 underlies all those outward phenomena of nature." 



