Potiok anpD Lronarp—On the Spectra of Cerium, Sc. 269 
Dipymium. 
A photograph was taken with the solution rich in didymium, 
but still containing some lanthanum, and giving a strong spectrum 
of the latter element. The slit was then lengthened, and a 
photograph of the spectrum of pure lanthanum superimposed on 
the first. ‘The long lines of the second spectrum thus cancelled 
all the lanthanum lines in the first spectrum, leaving the didymium 
lines as short lines between. 
The following are the measurements of the most characteristic 
lines, aad those marked with an asterisk appeared to be the most 
persistent :— 
Some Persistent Lints oF Dipymium CHLORIDE. 
Linear Intensity 
Measurement, Wave-length. and 
zi inch. Persistency. 
279°9 4792°8 Au No. 9 
293°7 4542°8 5 
298-1 4463°2 9 
308°8 4303°8 10” 
317-9 | 4177°5 10” 
399-9 3383°0 Au No. 15 
475-1 2946°8 oe 
485°3 2899°9 ore 
490°6 287671 3 
502°4 2825°6 Au No. 20 
CuemicaL Laporatory, 
Royvat CoLLtEcGEe or Scrence, 
Dustin. 
SCIENT. PROC. R.D.S., VOL. XI. NO. XXIII. 2 Ni 
