446 PROF. F. W. DYSON: DETERMINATIONS OF WAVE-LENGTH FROM SPECTRA 
The arc spectrum with which comparison was made contains 250 lines, including 
8 of intensity 10 and about 30 of intensity 7 or 8. Yet of the 32 lines given above, 
11 are not found in the arc spectrum and 4 are of intensity 1, while only 6 can be 
called strong arc lines. 
The line 354277, of intensity 12 in the spark and absent in the arc, and of intensity 
00 in the sun, is an exceptional case where an enhanced line does not appear in the 
chromosphere. 
Barium. 
The arc lines at 4554 and 4934 are strongly shown, and probably the line at 
5535-37, intensity 2, is the Barium line 5535-69. None of the enhanced lines are 
shown. 
Lanthanum. 
A number of strong arc lines are shown. These lines are all strong in the spark 
except (if due to La) 4105-07, which is of intensity 1 in the spark and 10 in the arc. 
Biit as there is an unidentified solar line at 4105"10 and the La arc line is given by 
Rowland as 4 105"03, it is possible that these lines are not identical, and that the 
chromospheric line agrees with the former. Enhanced lines at 3737"67 and 3871 "89 
are not shown, but 3517, 3713, 3790, 3949, 4196 are shown. 
Cerium. 
The spark spectrum of cerium has no very strong lines. Ten of intensity 10, 9, or 8 
are given by Exner and Haschek in the region considered, but the places of two are 
occupied by enhanced Ti and Fe lines. The remaining 8 are as follows:—- 
Spark. 
Chromosphere. 
Sun. 
Wave-length. 
! Intensity. 
Wave-length. 
No. of 
photos. 
Intensity. 
Wave-length. 
Intensity. 
3801-71 
8 
3801-62 
7 
3 
3801-68 
- C 0 Nd t 
4133-98 
10 
4133-83 
4 
1 
4133-97 
Ce 0 
4137-78 
9 
4137-54 
7 
3 
4137-57 
2 
4150-09 
10 
4150-10 
4 
2 
4150-06 
Ce 00 
4152-13 
9 
4152-14 
5 
2 
4152-11 
Fe-La 2 
4165-75 
10 
4165-71 
3 
2 
4165-76 
Ce -2 
4186-71 
10 
4186-76 
1 
1 
4186-78 
Ce-Zr, 2N 
4360-38 
8 
— 
The line 4137 is probably the solar line 4137'57, but not cerium ; cerium may have 
contributed to the lines at 4152 and 4186. The other lines are probably due to 
cerium, though the line 4133 is somewhat doubtful. The conclusion, slightly 
strengthened by the lines of intensity 5, 6, 7 in the spark, is that cerium is present, 
but very weak, in the chromospheric spectrum. 
