Decemder 18, 1903.] 



SCIENCE. 



773 



radiographed alone. The observations of 

 the late Pi-ofessor Ogden N. -Rood on the 

 delieetion of Roentjzen rays by crystal or 

 cut faces were verified. 



J. E. Burbauk iu 1S98 published a work 

 on mineral phosphorescence produced by 

 X-rays. Of all the substances tried, he 

 found 'in general minerals containing ores 

 of the metals are non-phosphorescent' and 

 that tiuorite and calcite seemed most suit- 

 able for experimentation. J. Trowbridge 

 states: "By them (X-rays) an electrical 

 charge is communicated to fluorescent and 

 phosphorescent substances. The resulting 

 electrical energy, in being dissipated (by 

 heat), produces the phenomenon of light" 

 (see below). Thomas A. Edison directed 

 the Roentgen rays upon some eighteen hun- 

 dred chemical compounds, artificial and 

 natural, seeking a fluorescent screen. Later 

 (1900) Bary examined the conduct of a 

 number of salts under the influence of 

 Roentgen rays. "Those which become 

 fluorescent belong, with the exception of 

 uranium, to the families of the alkalies and 

 alkaline earths. Similar results were ob- 

 tained by exposure to the radiations from 

 a radio-active metal supplied by Curie." 



Robert Boyle in 1663 appears to have 

 been the first to have made a truly scien- 

 tific examination of the phosphorescence of 

 diamonds, although the alchemist, Albertus 

 Magnus, in the thirteenth century, said he 

 had seen a diamond which glowed when it 

 was put in hot water. Bernouilli remarked 

 that when a diamond is rubbed on gold it 

 becomes luminous 'like a burnine coal ex- 

 cited by the bellows,' as Draper put it. 

 'A light, too, that cannot be extinguished 

 by water, and yet so ethereal and pure that 

 it can set nothing on fire' attracts the scien- 

 tific imagination as much to-day as it did 

 then. 



Two hj-potheses were offered iu the eight- 

 eenth century in explanation of phosphor- 

 escence; 



1. Lemery in 1709 maintained that phos- 

 phorescent bodies act like sponges to light, 

 absorbing it and retaining it by so feeble 

 a jiower that very trivial causes suffice for 

 its extinction. 



2. DuFay in 1735 held that it resulted 

 from actual combustion taking place in the 

 sulphureous parts of the glowing body. lie 

 first noted that the substance requires pre- 

 vious exposure to light ; it glows in the dark 

 with decreasing luminosity. DuPay also 

 observed the effect of interposing colored 

 glass between the phosphorescent body and 

 the light. 



In 1859 J. H. Gladstone exhibited dia- 

 monds strongly fluorescent iu the sunshine. 

 Silvanus Thomson used one of these dia- 

 monds in 1896 in a lecture on huninescence 

 at the Royal Institution. 



We are not oft'ering a complete history 

 of fluorescence or phosphorescence, nor ex- 

 planations of these fascinating properties; 

 but hints are given below which may serve 

 to assist in their elucidation. 



JIM. Mascart and Chaumet examined a 

 number of gems under the influence of 

 violet light. One of us (K.), in 1889, with 

 jNIascart. and with Ilallock in 1894, sub- 

 mitted bluish-white, opalescent diamonds 

 (from Bagagem ]\Iines, Brazil — tiffanyite) 

 to electric light passing through glass of 

 dift'erent colors. 



Although, as will be mentioned, such 

 compounds as alumina, alkaline earth sul- 

 phates and certain rare earth oxides, have 

 been examined in vacuum tubes under the 

 influence of electric sparks, we are not 

 aware of any very extended examination 

 of mineral or chemical substances when 

 subjected to ultra-violet light produced by 

 sparking. E. Becquerel in his 'La Lumiere, 

 ses Causes et ses Effects' states that 'the 

 electric spark acts only by its light, but its 

 action is more energetic than that of the 

 sunlight by rea.son of its great intensity 

 and the proximity of the source. ' "Wieder- 



