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which our eyes could not appreciate, just as we knew that there 

 were vibrations of sound that our ears could not appreciate. A 

 ray of light, split up in the spectrum, revealed the existence, at 

 either end of the visible part of the spectrum light, rays which 

 in the ordinary way could not be appreciated by the eye, — rays at 

 the red end, which produced heat, and rays at the violet end, 

 which were light rays known as the " ultra-violet " rays. It 

 was found, however, that certain substances possessed the power 

 of making these rays perceptible. Conspicuous among these 

 was fluor spar, upon the surface of which curious rays could 

 be seen playing. " Fluorescence " was the name at first given 

 to this peculiar property of fluor spar. A similar property in 

 the opal was known as " opalesence," but scientists, recognising 

 the effects to be of the same nature, now preferred to call the 

 quality "luminescence" wherever it occurred. These strange 

 surface rays were the invisible " ultra-violet " rays converted 

 into visible rays by the peculiar property of the surface of the 

 substances. On his table Mr. Payne had a number of solutions of 

 different " luminescent" substances, which in the ordinary light 

 appeared of one colour, while, when a strong light was thrown 

 upon them, they gave off their strange rays, and appeared of 

 quite a different tint. Some "luminescent" substances, even 

 after the light had been removed, retained, Mr. Payne explained, 

 their " luminescent " colour. For the purpose of illustrating 

 this he had placed a number of pieces of such substances in 

 partly exhausted tubes. Informing his audience that a strong 

 current of electricity passed through "luminescent" substances 

 at once brought out their peculiar qualities in a more conspicuous 

 manner than ordinary light, he went on to perform a number of 

 beautiful experiments with the substances in the tubes. Among 

 these were rubies, which, when the magic current was turned on, 

 glowed like living scarlet ; bits of marble, which shone under its 

 influence with a bright golden light ; and a bit of calcined shell. 

 Then there was what he called a " fancy tube," in which he had 

 placed a variety of substances with "luminescent" effects of 

 different colours. The result of the passing of the current 

 through this was a beautiful effect in purple and red that was 

 not unlike a vividly luminous thistle tiower. When the current 

 had been switched off, the brilliant glow gradually died out, like 

 the glow of a cooling ember. Mr. Payne was careful to point 

 out that even when the glow was brightest the substances were 

 quite cold. 



It was, he went on to say, in the course of investigations of 

 the phenomena of fluorescence that the strange effects produced 

 by the " X" rays were stumbled upon. Professor Eontgen had 

 succeeded in discovering how, by means of the current in the 

 vacuum tube, to transfer the "cathode'' rays set up within 

 the tube to outside it, so as to render " fluorescent" a screen of 



