MORSE. — THE KATHODO- LUMINESCENCE OF FLUORITE. 7 



turned through 90° and a new face presented, so that the exposure 

 coukl be continued to about two hours with a single crystal. The 

 luminescence light passes almost undimmed through the thin layer of 

 color on the face of the crystal, so that a face which has been completely 

 protected from further excitation by the kathode beam is still quite 

 transparent to light, and may therefore be turned toward the slit, while 

 a new face is exposed to excitation. 



The tube was kept connected with the pump during the entire series 

 of experiments, and the vacuum was brought back to the most favorable 

 point whenever necessary. For some crystals no pumping was required, 

 and the vacuum remained at the right point for many hours. In other 

 cases constant use of the pump was necessary. The Westmoreland 

 crystal (No. 3), although one of the clearest and least colored of the 

 series, gave off hydrogen in measurable quantities, and the spectrum 

 of the gases in the tube changed slowly after this crystal was introduced, 

 until finally the original nitrogen (air) spectrum had almost entirely dis- 

 appeared and only hydrogen was visible. This is evidently closely con- 

 nected with the fact that this same Westmoreland fluorite contains a 

 considerable percentage of hydrogen in the gases which it holds oc- 

 cluded. Analysis of the gases given off from this fluorite on heating 

 showed that while the amount of gas present was small compared with 

 some other fluorites, it contained about 52 per cent of hydrogen.^ The 

 evolution of hydrogen at room temperature, under the influence of 

 the kathode discharge, is an interesting qualitative confirmation of the 

 analyses. 



IV. In the following tables the abbreviations 



sh., sharp v. sh., very sharp 



dif , diffuse v. dif , very diff"use 



q. sh., quite sharp max., maximum 



are used. Bands are indicated by brackets enclosing the numbers 

 representing their boundaries. 



Intensities are given on a scale of 1 to 10, int;reasing. 



In tables IX and X the strong' lines and those common to several 

 crystals have been collected. A few important relations may be men- 

 tioned. 



The band from X 5570 to A 5610 is a universal constituent of all 

 these spectra. 



The strong line at X 5667 is present in all but one. It is just as cer- 



' See also Humphreys, Astrophysical Journal, 20, 2G6 (1904). 



