On Radiant Matter. g 



diamond shines with as much light as a candle, phosphor- 

 escing of a bright green. 



Next to the diamond the ruby is one of the most remarkable 

 stones for phosphorescing. In this tube (Fig. 4) is a fine col- 

 lection of ruby pebbles. As soon as the induction spark is 



FIG 4. 



turned on you will see these rubies shining with a brilliant 

 rich red tone, as if they were glowing hot. It scarcely 

 matters what colour the ruby is, to begin with. In this tube 

 of natural rubies there are stones of all colours the deep 

 red and also the pale pink ruby. There are some so pale 

 as to be almost colourless, and some of the highly-prized 

 tint of pigeon's blood ; but under the impact of Radiant 

 Matter they all phosphoresce with about the same colour. 



Now the ruby is nothing but crystallised alumina with a 

 little colouring-matter. In a paper by Ed. Becquerel,* 

 published twenty years ago, he describes the appearance 

 of alumina as glowing with a rich red colour in the 

 phosphoroscope. Here is some precipitated alumina pre- 

 pared in the most careful manner. It has been heated 

 to whiteness, and you see it also glows under the molecular 

 discharge with the same rich red colour. 



The spectrum of the red light emitted by these varie- 

 ties of alumina is the same as described by Becquerel 

 twenty years ago. There is one intense red line, a little 

 below the fixed line B in the spectrum, having a wave- 

 length of about 6895. There is a continuous spectrum be- 

 ginning at about B, and a few fainter lines beyond it, but 

 they are so faint in comparison with this red line that they 



* Annales de Chimie ct de Physique, 3rd series, vol. Ivii., p. 50, 1859. 



