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POPULAR SCIENCE MONTHLY. 



NEW SOURCES OF LIGHT AND OF RONTGEN RAYS. 



By HENRY CARRINGTON BOLTON, Ph. D. 



AMONG the general laws of physical science, none seems more 

 firm!}' established than that of the conservation and correlation 

 of energy; according to this the various forms of energy that constitute 

 the domain of experimental physics, heat, light, electricity, magnetism 

 and chemical action, have reciprocal dependence and "can not originate 

 otherwise than by devolution from some preexisting force," or rather 

 energy. That motion is convertible into heat, heat into light and both 

 the former into electricity are phenomena familiar to every one who 

 uses incandescent bulbs or rides in a trolley, and we do not usually 

 recognize any production of light unaccompanied by heat. True, the 

 little fire-fly is possessed of a mysterious power that enables it to emit 

 light without enough heat to affect Langley's most sensitive bolometer, 

 but the eminent Secretary of the Smithsonian has to admit that the 

 "cheapest form of light" is produced by "processes of nature of which 

 we know nothing." This little understood property called phosphor- 

 escence is shared by many living organisms, both animal and vegetable, 

 as well as by substances of the mineral kingdom; to the former belong 

 coelenterates, mollusks, Crustacea, fishes and insects, and decaying 

 wood, certain mushrooms, etc.; to the latter the Bologna stone, so-called, 

 and the commercial article called 'Balmain's paint.' 



In the case of the mineral substances, barium or calcium sulfids 

 and the like, the light-giving power is not an innate property, but is 

 set in operation by exposure to the energy of sunlight, the light of 

 burning magnesium or to some other source of actinism; moreover, 

 the power thus acquired by insolation is a fugitive one, the substances 

 exercising it after three or four hours become 'dead' and lose their 

 activity. Excepting then these living beings and these phosphorescent 

 bodies, light as commonly known to ns is always correlated with heat; 

 within the last four years, however, discoveries have been made in 

 France that seem to modify the position taken by philosophers and to 

 necessitate new views concerning the manifestations of that energy with 

 which the universe is endowed. A group of French savants have found 

 mineral substances that apparently give out light perpetually without 

 any exciting cause, realizing the dream of the alchemists — a perpetual 

 lamp consuming no oil. These substances also emit rays having the 

 penetrating properties of X-rays, other rays affecting a photographic 



