406 Mr. H. Jackson on Phosphorescence. 



way to give rise to green light, and in like manner for the 

 red, orange, and blue specimens. Whether it will be possible 

 or is in the nature of things to separate out the different 

 kinds in a state of purity can only be decided by further 

 experiment. 



The examples of different forms of lime have been so far 

 exhibited only under the conditions obtaining in a high vacuum 

 with an electric discharge. Before trying to show the points 

 in common between these phenomena and the phenomena of 

 phosphorescence in other conditions, it may be as well to 

 consider briefly the character of the action in a high vacuum. 

 The suggestion which follows is not intended to be anything 

 but an imperfect attempt to bring all the phenomena of phos- 

 phorescence into line with one another. 



When a discharge passes through a vacuum there can be 

 little doubt that the transferring medium is the residuum of 

 gas in that partial vacuum. If the particles of this gas behave 

 as visible masses are seen to do, they are probably attracted 

 or are driven to the electrode at high potential. Receiving 

 the same kind of charge as this electrode, they fly off from it 

 in that charged condition. 



But if these particles consist of more than one unit, each 

 unit, after the group has travelled a certain distance from the 

 electrode^ must repel each other unit in the same way as the 

 whole little group was repelled from the electrode. If, how- 

 ever, the units making up the group are held together by 

 that something which is called chemical attraction, a condition 

 of strain is set up in which the electrical repulsion is striving 

 to overcome the chemical attraction. Travelling unimpeded 

 through the high vacuum, this condition of strain would be 

 maintained until the charged group met with something 

 capable of discharging it. At that moment of discharge the 

 chemical attraction would assert itself; there would be a 

 rushing together of the units composing the group, and an 

 over-rushing, whereby oscillations would be set up. These 

 oscillations, considered as blows or pulses either directly or 

 sethereally transferred to a substance, would set it in turn 

 oscillating in a manner fitted to its own molecular structure; 

 and its oscillations would in their turn give rise to the undu- 

 lations which appeal to our eyes as the phosphorescent light. 

 If instead of the discharge taking place on a substance capable 

 of responding to and absorbing most of the energy of the con- 

 sequent oscillations it were to occur on glass, platinum, or 

 any of the materials which have been employed, it is con- 

 ceivable that the oscillations would appear as short sethereal 

 waves, or in other words as Rontgen rays. In the case of a , 



