Seventeenth annual Meeting. 105 



an account of a chlorophane from Virginia and one from Siberia, which passes from light 

 green to a line emerald green as the temperature rises, but no mention is made of a 

 change of hue, although the mineral was placed on a live coal. I was sufficiently in- 

 terested to investigate further. If the fragment he cooled when emitting either the 

 green or the purple light and he heated again, the light which it was giving when 

 cooled will return. Thus, if giving purple light and then cooled and again heated, it 

 does not now fust give the green, but emits the purple as soon as it reaches the tempera- 

 ture at which it became non-luminous. It was found also that the several specimens 

 became luminous at temperatures ranging from 100°-110°C., and that the purple violet 

 tint appeared at 170°-1SO°C. It was impossible with the Hg. thermometer to measure 

 the temperature at which the tluorite lost the power of phosphorescence, but it was be- 

 low a red heat in the form of the experiment tried by me. It is by no means a matter 

 of indifference whether the temperature rises slowly or rapidly in exciting phosphor- 

 escence. A piece of the mineral was broken into two nearly equally portions. One of 

 these was heated rapidly, the other slowly. That rapidly heated emitted a fine green 

 which was succeeded by a distinct and moderately deep purple. The slow heating was 

 accomplished by placing the mineral on the edge of a metal plate heated in the center 

 by a gas tlaine. It became faint green as soon as it became warm. Presently the light 

 entirely disappeared; on moving the mineral to a warmer part of the plate, the green 

 phosphorescence again appeared, to disappear and reappear as before. At length it lost 

 the power of phosphorescing by increasing the temperature. In other words, its power 

 to emit light was gone. In this case of slow heating only the faintest approach to a 

 violet tint was perceptible. I have no doubt that by careful manipulation it might 

 have been made to yield pure green light only; and indeed, I believe that if the tem- 

 perature be very slowly raised these specimens of fluorite would ultimately lose the 

 power of giving out phosphorescent light at any temperature without at any time be- 

 coming luminous. Experiments upon this point have not been entirely conclusive, but 

 have indicated this result. If it be true that by slow heating, specimens which more 

 rapidly heated give both green and purple light, yield only green light, and that if very 

 slowly heated no phosphorescent light wild be given out however high the temperature 

 be raised, then the molecular change, whatever it be, that causes phosphorescence, and 

 which when effected precludes the recurrence of the phenomenon, may be produced so 

 slowly as to emit no light whatever. 



The specimens of fluorite from Colorado, like those from the localities previously 

 mentioned, became phosphorescent by friction, best against each other, but also against 

 other minerals and metals. The friction need not be very great to elicit light. This 

 result is well shown by holding a piece of the mineral on a grindstone. The abraded 

 powder remains luminous for a time, making a streak of light as the stone revolves. 

 ( Mher specimens of fluorite in our cabinet do not show this change of color, and do not 

 become phosphorescent by attrition. 



CHRISTENING AMETHYST MOUNTAIN. 



BY J. SAVAGE. 



Amethyst Mountain is situated upon the East fork of the Yellowstone, in the Na- 

 tional Park, and was so named by Prof. F. V. Hayden during the summer of 1872, under 

 tin' following circumstances: 



The main party of Hayden's Geological Survey were camped in Cache valley, near 

 the mouth of the East fork of the Yellowstone, while Prof. Hayden, SirWm. Blackmore, 

 our English -nest, and a few others, made a hurried trip to the headwaters of Clark's 



