OF ARTS AND SCIENCES. 



403 



with those computed in the table below. The " intensity " or heavi- 

 ness of the lines has been estimated roughly by the eye, taking the 

 intensity of b^ as unity. The mean of three separate estimations is 

 given upon the next page, and these intensities have been used in 

 forming the chart, Plate II. For convenience the wave-lengths X, 

 and intensities I. are placed together in a table upon page 404. 



TABLE OF WAVE-LENGTHS: — Group "i." 



