Mr. H. Jackson on Phosphorescence. 413 



If either of the mantles mentioned be introduced into a 

 tube and treated with an electric discharge in a high vacuum 

 the phosphorescent glow can be studied either with or without 

 the heating effect. The glow of the Welsbach mantle is 

 a greenish white but not very marked. The Sunlight mantle 

 gives a fine red glow. It is interesting to note that the glow 

 shows great persistence even when the temperature of the 

 substance has been raised considerably by the vigour of the 

 bombardment. 



Having now dealt with the last source of oscillation which 

 it was proposed to consider, it may be as well to summarize 

 the conclusions which for the present seem to be the least 

 open to objection so far as experimental evidence goes. The 

 attempt has been made to connect together all the phenomena 

 of phosphorescence with a view of showing between them a 

 likeness in kind. Any theoretical suggestions should be 

 taken only as hypotheses for assisting this attempt and for 

 pointing the direction of further experiments. It is believed 

 then that the following typical examples of the various phe- 

 nomena which are described as phosphorescent phenomena 

 are similar in kind and can be related to one another by the 

 application of slight modifications of the same general principle 

 — the glow of phosphorus, the fluorescence of quinine, the 

 sparkling of heated chlorophane, the luminosity of Bal- 

 main's paint, the light from lime in a vacuum-tube, and the 

 glowing of barium platinocyanide under the influence of 

 Arrays. To these it is proposed to add coloured flames and 

 the spectral light of glowing gases. It is suggested that all 

 these phenomena may be looked upon as outward evidences 

 of response on the part of the substances to rapid oscillations, 

 whether these oscillations have their origin in chemical com- 

 bination, in what is commonly spoken of as light, or in elec- 

 trical discharge. The nature of that response may in some 

 cases be of a direct character ; but, when account is taken 

 of the many degrees of persistence of phosphorescence and of 

 potential phosphorescence, it seems in many cases first to 

 assume the form of something which to avoid circumlocution 

 may be called a statical charge. The release of this con- 

 dition of strain is accompanied by oscillations which give rise 

 to the visible undulations of the phosphorescent light. 



One final suggestion may perhaps be made, though it is 

 mentioned with diffidence, as many may consider it outside 

 of the subject. 



If it be accepted that the light of the sun has its immediate 

 origin mainly in the masses of luminous clouds floating in 

 the photosphere, and if these clouds be considered as con- 

 densations into material of greater molecular complexity than 



Phil. Mag. S. 5. Vol. 46. No. 281. Oct. 1898. 2 G 



