May 5, 1911] 



SCIENCE 



697 



rescence can be excited. Lenard regards tlie 

 phosphorescence spectrum as consisting of one 

 or more well-separated, broad and continuous 

 bands usually lying within the visible spec- 

 trum. Detailed study of these bands with the 

 ►/spectrophotometer," however, shows that they 

 are really of a very complex structure and con- 

 sist of overlapping components which can not 

 be separated altogether for any given tempera- 

 ture or mode of excitation, but which are so 

 differently affected when the wave-length of 

 the exciting light is varied or when excitation 

 occurs at different temperatures, as to indicate 

 that they are not due to the luminescence of 

 one and the same molecule or aggregate. It is 

 probably on account of this complexity of the 

 phenomena that Lenard has reached his view 

 of the case. Certainly the evidence of recent 

 work by Pierce,* Waggoner'' and Zeller" goes to 

 show that whatever may be true of phospho- 

 rescent sulphides prepared by the method of 

 Lenard and Klatt, the relation between phos- 

 phorescence and fluorescence is in many other 

 instances the intimate one that has usually 

 been assumed to exist. 



Fluorescence in the Ultra-Violet and the 

 Infra-Red.' — Stark and Meyer' have in a recent 

 paper shown the existence of numerous fluo- 

 rescence bands lying in the ultra-violet spec- 

 trum. In the case of the benzol derivatives 

 with which their measurements have to do 

 fluorescence depends for its position upon the 

 complexity of the molecule and it is found 

 that, as a rule, the heavier aggregations have 

 bands in the longer wave-lengths. 



Steubing' finds spectrum lying at still 

 shorter wave-lengths (.1884m) which he as- 

 cribes to the fluorescence of oxygen. This 



^ Nichols and Merritt, Physical Beview, Vol 

 XXXII., p. 38. 



' Pierce, C. A., Physical Beview, Vol. XXVI., pp, 

 312 and 454; XXX., p. 663. 



= Waggoner, C. W., Physical Beview, Vol. XXX. 

 p. 663. 



' Zeller, C. A., Physical Beview, Vol. XXXI., p 

 367. 



' Stark and Meyer, Physihalische Zeitschrift. 

 Vol. 8, p. 250. 



' Steubing, Annalen der PhysiTc (4), Vol, 

 XXXIII., p. 553, 1910. 



spectrum, like the corresponding spectra for 

 vapors of gases having fluorescence in the 

 visible spectrum, as described by Wood," con- 

 sists of a group of bands regularly but not uni- 



Fig. 1. Diagram sbowing the distribution and 

 relative intensity of bands in the fluorescence 

 spectrum of oxygen (Steubing). 



formly spaced. As may be seen in Fig. 1 

 the distance between the bands increases 

 gradually with increasing wave-length. Be- 

 ginning at that end of the group which 

 lies furthest in the ultra-violet, the inten- 

 sity of the individual bands rises very 

 rapidly to a well-marked maximum and falls 

 off more slowly as the wave-length increases. 

 An inspection of the remarkable photographs 

 made by Wood of the fluorescence of sodium 

 and other vapors leads one to believe that were 

 measurements made of those spectra a similar 

 distribution of intensities would be found to 

 exist. 



Pauli" has recently subjected the prepara- 

 tions of Lenard and Klatt to systematic study, 

 particularly with the view of corroborating 

 Lenard's hypothesis that the active metallic 

 atom embedded in the sulphide is to be re- 



'Wood, Philosophical Magazine (6), Vol. X., 

 p. 513; Vol. XV., p. 581; Vol. XVI., p. 184. 



"Pauli, Physikalische Zeitschrift, Vol. XI., p. 

 991. 



