152 FLUORESCENCE OF THE URANYL SALTS. 



In the spark spectrum of lead, of the 9 lines listed by Haschek which 

 lie in the fluorescence region, 7 are within one frequency unit of our 

 readings of the corresponding bands; 4 of these are in practically 

 perfect coincidence, the departures from the crests of the bands being 

 only one or two tenths of a unit. 



Of the 25 spark lines of zinc within the fluorescence region, 15 are 

 certainly not related to fluorescence in the manner here under con- 

 sideration, 4 in somewhat doubtful coincidence, and 6 are in close 

 approximation. Of these last, 5 are consecutive lines of the spark 

 spectrum, all of which are in group 7 of our fluorescence system. The 

 evidence of any significant relation based upon these coincidences is 

 obviously far from conclusive. The matter is mentioned here solely 

 in view of possible developments in the further study of the connection 

 between fluorescence and temperature radiation. 



The search for possible coincidences in the case of sodium led to the 

 discovery of a striking arrangement, which seems to be peculiar to that 

 element. The doublets and triplets of the spark spectrum, while they 

 do not form constant-frequency series, are so located that they could 

 be excited to radiation of the type described by Wood, with a common 

 interval equal to the fluorescence interval of the acetates; i. e., about 

 85, the result would be a well-defined group spectrum of the type of the 

 fluorescence spectrum of the uranyl salts. (See fig. 85.) There are, 

 however, only two individual coincidences with bands of the sodium 

 uranyl acetate. 



In the figure, the actual arc-lines of sodium are elongated. The 

 shorter lines are derived from them by assuming constant-frequency 

 series having the interval 85, as described above, 



FLUORESCENCE SERIES IN THE SPECTRA OF THE DOUBLE ACETATES. 



In tables 58 to 70 the fluorescence bands in the spectrum of the double 

 salts are arranged in the order of their wave-length. In tables 71 to 

 83 the frequencies and average intervals of each series in the various 

 salts are given. It will be seen by comparison with tables 56 and 57 

 that the average interval for the double acetates is less by more 

 than one frequency unit than for the single acetates ; also that the av- 

 erage for the various double salts differ from the general average of all 

 (table 84) by an amount no greater than the difference between the 

 intervals of the various series present in the spectrum of a given salt. 

 In brief, whatever real differences may exist are too small to be deter- 

 mined from our data. 



