332 Scientific Proceedings, Royal Dublin Society. 
It was not considered necessary to reproduce the photographs 
of all the spectra; but Plate XX VI. shows the spectra given by 
a strong solution and a dilute solution of each of the three 
elements; and the most persistent lines are indicated by one, two, 
or three dots placed under them, accordingly to their persistency, 
and Plate XXV. shows the complete series of photographs for 
vanadium. 
‘In the Tables of wave-lengths, double lines, the wave-lengths 
of only one of which is given, are indicated by two dashes after 
the intensity: thus 10”; the persistency of the lines is indicated 
by Greek letters, thus :— 
@ seen with 1 °/, solution not seen with 0-1 °/, 
Noo sar Nate Oa a eae #4 DO, 
CI ee en ee OOO), 
Gh) yd tae tO OOS RIES 
The photographs of spectra extend from 5890 to  2544°3, 
and were taken by a one-prism quartz spectrograph by Hilger. 
The measurements were made by one of Hilger’s micrometers, 
and these were afterwards reduced to wave-lengths by use of a 
eurve for the identification of the lines. Im each case the 
micrometer was set so that gold line No. 9 was at 280-0, that 
point corresponding with its position on the curve used. The 
wave-lengths given are those generally accepted, but in every 
case the measured wave-lengths agreed very closely, so that 
there could be no possible doubt of the identity of the lines. 
