770 



SCIENCE. 



[N. S. Vol. XVIII. No. 468. 



tliem meaning the same. Perhaps they are 

 "in reality the same phenomena ; but in this 

 paper by fluorescence we mean a lumin- 

 osity, more usually evidencecl by a play of 

 color, lasting only during the direct influ- 

 ence of the exciting agent. By phosphor- 

 escence, we mean the emission or propaga- 

 tion of ethereal stresses, which affect the 

 optical centers, producing light, white or 

 colored, which persists after the removal 

 of the cause. Substances may, therefore, 

 be both fluorescent and phosphorescent. 



The radium preparations of the highest 

 activity used in these investigations became 

 the property of the American Museum of 

 Natural History through the liberality of 

 Mr. Edward D. Adams, a member of the 

 Board of Administrators of the Museum 

 and of the New York Academy of Sciences. 

 His gift of the necessary funds was ap- 

 plied to the purchase of one portion of 

 radium bromide of 300,000 activity and 

 another of 1,800,000; uranium being taken 

 as the standard at 1. The' preparations 

 were obtained from the Societe Centrale 

 des Produits Chimiques at Paris. Unfortu- 

 nately, although the order was authorized 

 and material assured, it has been impossible 

 to obtain the bromide of the highest ' 

 strength in time for presentation at this 

 meeting. The results here announced have 

 to do with the radium of 300,000 and of 

 7,000 activity (chloride) and 240 (chloride) 

 and of 100 radium barium carbonate. The 

 compounds of lower activity were pur- 

 chased by the authors. 



The intense penetrative powers of ra- 

 dium preparations have been previously 

 noted by numerous investigators — as the 

 Curies, Strutt, Rutherford and others- 

 mentioned later. The bibliography is so 

 extensive that no effort is made to give all 

 the references in this abbreviated paper. 

 A remarkable illustration, almost startling, 

 of its penetration was demonstrated with 

 the following experiments: Radium bro- 



mide of 300,000 activity was placed in a 

 sealed glass tube contained in a rubber 

 thermometer-holder, the top of which was 

 tightly screwed down, and the whole placed 

 in a water-tight tinned-iron box; over the 

 box were placed, first, a heavy silver tureen 

 1.5 mm. thick, then four copper plates, 

 such as are used for engraving, and finally 

 a heavy graduated measuring-glass 10 em. 

 in diameter filled with water to a depth of 

 15 cm. A diamond was then suspended 

 in the water and became fluorescent im- 

 mediately. Whenever the tube with ra- 

 dium was withdrawn a distance of more 

 than one meter, the fluorescence ceased, 

 but was resimied on replacing the radium 

 under the tureen. This experiment showed 

 that the influence of the radium was ex- 

 erted successively through glass, rubber, 

 silver 1.5 mm. thick, four copper plates, 

 glass 0.5 cm. thick, and finally 8 cm. of 

 water. 



AA^ith all these wonderful properties of 

 radio-activity, there is yet a certain amount 

 of discussion at the present time between 

 the German and the French investigators. 

 Some of the former say that radium of 

 300,000 activity seems to them improbable ; 

 and that no scientific man should take this 

 expression seriously. They believe that if 

 metallic radium is ever obtained its ac- 

 tivity will not exceed 100,000. This view is 

 reiterated by others, Avho also state that 

 these activities are only surmised, that they 

 are not accurately determined, and can not 

 be sustained by definite measurements. 

 Madame Curie unhesitatingly speaks of 

 the difficulties attending accurate measure- 

 ments of such high radio-activity. 



Incidentally it may be well at this point 

 to call attention to the complex nature of 

 these radiations. While a number of re- 

 searches from such physicists as Becquerel, 

 Professor and Madame Curie, Meyer and 

 von Schweidler, Giesel, Elster and Geitel, 

 Villard and Rutherford have proved the 



