302 W. P. Headden — Some Phosjrfwrescent Cm 1 cites. 



The yellow calcite alone possesses the property of phosphor- 

 escing in the sense that I nse this term. The first sample 

 which we found to possess this property had an irregular 

 purple patch near its center, which appeared as a dark area in 

 the mass of yellow light. Repeated observations on cleavage 

 pieces which were partly yellow and partly of some other 

 color fully justify the preceding statement. In such cases the 

 phosphorescence was always limited by the line of growth 

 which marked the change from the yellow to the other color, 

 whatever it was, white, purple or colorless. 



The duration of this phosphorescence in the yellow calcite 

 was as much as thirteen hours, which was established hj con- 

 tinuous observation. The duration actually exceeded this time, 

 but one's eyes and judgment too become more or less unre- 

 liable after hours of watching, especially as this light not only 

 becomes very feeble, but also assumes a ghastly whiteness 

 before it fades out entirely. The phosphorescence was dis- 

 tinctly visible, however, in some specimens, for the time given, 

 thirteen hours. 



These experiments were made in both the summer and win- 

 ter seasons. An insolation for any considerable time in the 

 summer season produced a sensible increase in the temperature 

 of the mass ; this probably had some effect upon the intensity 

 and duration of the phosphorescence in the samples observed 

 at that time r I insolated a large specimen for thirty minutes 

 at a temperature of —3° C, when it was found to be strongly 

 phosphorescent. I did not determine the duration of this 

 phosphorescence, but I could not perceive any diminution in 

 its intensity at the end of two hours. A variation of tempera- 

 ture from —3° to +25° C. does not, so far as our observation 

 goes, materially affect the character and duration of the phos- 

 phorescence. 



I endeavored to observe whether this phosphorescent light 

 would give a spectrum or not ; but the results were unsatis- 

 factory. The action of this light on a photographic plate was 

 tested by exposing a Seed's gilt edge dry plate to the action of 

 the light emitted by a large, strongly phosphorescent crystal 

 for 30 minutes. The portions of the plate intended to receive 

 the action of the light were not protected in any way. There 

 was no action at all on the plate, it was perfectly clear when 

 developed. 



Phosphorescence can be excited in the yellow calcite by the 

 electric spark, also by the X-ray. The phosphorescence excited 

 by the passage of the spark for a few seconds was observed 

 for thirty minutes, but it had in this time become quite faint. 

 A number of cleavage pieces of the Joplin mineral of different 

 colors and a piece of Iceland spar were exposed to bombard- 

 ment by the X-ray : they all became phosphorescent, but the 



