780 



SCIENCE. 



[N. S. Vol. X\ail. Xo. 408. 



'grounded' by placing directly upon the 

 iron radiator in the room and similar ob- 

 servations made, as when the precious 

 stones were insulated. 



It is interesting here to note that Marck- 

 wald reported the property of phosphor- 

 escence with polonium as belonging only 

 to Brazilian diamonds. Rosenheim found 

 that the rays from radio-active polonium 

 possess the property of inducing fluores- 

 cence in a number of diamonds from differ- 

 ent localities. The rays emitted by the 

 diamonds under these conditions affect the 

 retina and the photographic plate. ' ' This 

 actinic, activity of the diamond," he says, 

 "like its visible fluorescence, is entirely de- 

 pendent on the presence of the polonium, 

 not persisting after the removal of the lat- 

 ter. Even after long exposure to polonium 

 rays no induced radio-activity could be 

 detected." We found, the fourteen and a 

 half carat diamond from Brazil very re- 

 sponsive to the polonium ; also some from 

 British Guiana. 



Almost all diamonds, of various weights 

 and from many localities and of different 

 colors, fluoresce and phosphoresce more or 

 less with radium, except the black or car- 

 bonado. The degree to which these phe- 

 nomena are observed is no criterion of the 

 grade of the gem, however, as stones with 

 flaws often fluoresced with even greater 

 brilliancy than the pure ones. 



8. It is quite evident through our study 

 of the collection, that one or the other of 

 these forms of luminosity and activity may 

 have a value to detect elements or com- 

 pounds that have escaped notice or are 

 present in the minerals as impurities. 

 These forms of investigation may also 

 prove serviceable in chemical analyses. 

 There should be a use for this line of re- 

 search also in petrological determinations, 

 as the slightest phosphorescence or fluores- 

 cence would aid in determining and locat- 

 ing a mineral, no matter how minute in 



quantity. Thi.s we have done in several 

 instances. 



The original ultra-violet lamp was that 

 of Gorl, of Munich, altered by the English 

 into the St. Bartholomew lamp, and again 

 improved and made practicable in the 

 United States under the name of the Pif- 

 fard lamp, after Dr. H. G. Piffard, of New 

 York. It is an instrument of great utility 

 and, in the convenient form with which we 

 worked, can not fail to prove a valuable 

 mineralogical and chemical as well as med- 

 ical adjunct. In fact. Dr. Piffard has used 

 it with much success in medical practice. 

 It will also be useful in many instances 

 for mineralogical determinations— at times 

 to detect impurities which have escaped 

 analysts and others. 



9. In all observations on the effect of 

 radium, ultra-violet light and the X-rays 

 to determine whether an object becomes 

 fluorescent or phosphorescent under the 

 influence of either, it is essential that the 

 eyes become thoroughly accustomed to the 

 change of conditions when one is in a dark 

 room. This usually requires from ten to 

 twenty minutes, and in some cases half an 

 hour. Attention has been called to this 

 by preceding observers. Whether it be 

 due to the accumulation of the visual pur- 

 ple, which von Kries states is a substance 

 that supplies the retinal basis of vision at 

 low luminosities, and whose accumulation 

 is accountable for the great increase in 

 sensitiveness of the dark-adapted eye, or 

 to the ordinary physical changes in the 

 optical lenses, or partly to both, we do not 

 undertake to decide. But it was found 

 to be advisable that just before the source 

 of excitation was removed from the ma- 

 terial examined, the eyes be closed, and not 

 opened again until after the removal. 

 Else, as was noted, the residual flash that 

 remained might be mistaken for phos- 

 phorescence. In most of the experiments 

 carried on, three observers watched each 



