256 ON THE ULTRA-VIOLET Si'KUTRA OF THE ELEMENTS. 



NOTE ON THE MAPS OF THE SPECTRA OF COBALT AND NICKEL. 



These maps contain many lines which are not in the list in the text. These 

 additional lines were observed in the arc between carbon electrodes when metallic 

 cobalt and nickel respectively were introduced into it ; but they were not included in 

 the list in the text because the authors were unable, for the reasons given in the text, 

 to be quite sure that they were not due to other metals contained in the carbon 

 electrodes, or in the crucible in which the arc was taken. It is most probable that 

 the greater part are really due to the metals to which they are assigned in the maps. 



The reader is referred to the list in the text for the measured wave-lengths, as, 

 owing to a parallactic error in ruling, many of the lines in the maps are placed a 

 fraction of a tenth-meter out of their true places. 



