The luminescence produced by heat is wonderfully marked in the case of chlorophane, a variety of fluorite. A Siberian specimen of a pale violet color emitted a white light merely from the heat of the hand; boiling water caused it to give out a green light, which was so greatly intensified when the specimen rested on a live coal that the radiance could be discerned from a considerable distance. Similar phenomena were observable in the case of chlorophane from Amelia Court House, Va., and the writer found that specimens from this source also exhibited strong triboluminescence, resulting either from contact with one another, or with any hard substance.[261] As the terms fluorescence and phosphorescence are sometimes rather carelessly employed, it may be well to note here that while both terms are used to denote the luminescence of a non-luminous body resulting from the action of light rays, of the electric current, or of radiant energy of any kind, as well as from heat, fluorescence signifies a luminosity which only continues so long as the exciting cause is present, while phosphorescence means a luminosity persisting for a longer or shorter period after the exciting cause has ceased to operate directly. The latter term therefore denotes a luminous energy stored up in the formerly non-luminous body and emitted by it for a certain time, at the expiration of which it again becomes non-luminous. Other special designations of induced luminosity in minerals are triboluminescence, the emission of light as a result of friction and thermoluminescence, a term used to denote light-emission excited by moderate heating, even by the warmth of the hand. An old treatise in Greek, said in its title to come from “the sanctuary of the temple,” and containing material, partly of Egyptian origin, may help us to understand something of the processes employed by a temple priest to impress the common people by the sight of luminous gems. The writer of the treatise declares that for the production of “the carbuncle that shines in the night” use was made of certain parts (he says “the bile”) of marine animals whose entrails, scales and bones exhibited the phenomenon of phosphorescence. If properly treated, precious stones (preferably carbuncles) would glow so brightly at night “that anyone owning such a stone could read or write by its light as well as he could by daylight.”[262] In the _Annales de Chimie et Physique_, the great French chemist, M. Berthelot, discusses this matter and expresses the following opinion[263]