Froc., 



72. 



THE ULTRA-VIOLET SPECTRUM OF RADIUM. 



The Collotype illustrations are from the original negatives, 

 and are entirely untouched. The grain of the process somewhat 

 diminishes the sharpness of the lines. 



To economise space and avoid unnecessary complications, I 

 have given photographs of only that part of the spectrum 

 adjacent to the radium lines. Had the whole spectrum been 

 given as photographed, the length would have extended to more 

 than 10 feet. 



The upper half of each strip shows the iron lines used as 

 standards, with their wave-lengths according to Rowland's latest 

 measurements. The lower halves contain the radium lines, with 

 their wave-lengths as calculated from the iron standards. The 

 other lines on the lower halves are chiefly platinum lines. On the 

 4th and 5th photograph a strong barium line is shown at wave- 

 length 3891-97 (Rowland), or 3892-42 (Exner and Haschek). 



In the part of the spectrum shown on the last strip there are 

 no iron lines suitable for standards. Here, therefore, I have used 

 some good lines of zinc and cadmium the wave-lengths of which 

 are given in Rowland's latest table. 



