ON THE TOTAL ECLIPSE OF THE SUN, MAY 28, 1900. 41 1 
prominences consists of the radiations which are brightest in the spectrum of the 
chromosphere. 
Heights of Chromospheric Vapours. 
Measurements of the lengths of the arcs photographed at the oommencemeiit 
of totality have been made in order to determine the heights above the photosphere 
to which the corresponding vapours are visible. The results obtained from measure¬ 
ments of photograph No. 2 of the 20-foot series are shown in the following table, 
in which the corresponding results obtained in 1898* are introduced for purposes 
of comparison. 
Heights of Chromospheric Vapours. 
Heights in Seconds of Arc. 
Heights in Miles. 
Lines. 
1900. 
1898. 
1900. 
1898. 
Proto-calcium (K). 
13-0 
13-3 
5900 
6000 
Hydrogen. 
8-9 
10-0 
4000 
4500 
Helium (4471 • 65). 
8-7 
8-9 
3900 
4000 
Strontium (4077'89). 
6-7 
6-0 
3000 
2700 
Strontium (4215-70).1 
Helium (4026 • 34)./ 
5-8 
6-0 
2600 
2700 
Calcium (4226 • 90). 
4-1 
4-4 
1850 
2000 
Titanium (3761-46). 
3-6 
_— 
1600 
-- 
Scandium (4247-00). \ 
Mg ultra-violet triplet (3832-45) . . . . J 
3-4 
4-4 
1500 
2000 
Ti enhanced lines (4572 -16, Ac.). 
3-3 
— 
1500 
- - 
Fe triplet (4045 - 98, &c.).'] 
A1(3944-16, 3961-67) . } 
h .3 (Mg) (5183-79, &c.).J 
2-6 
3-2 
1180 
1450 
Mn quartet (4030-92, &c.).\ 
2-4 
•> • 4. 
1090 
1100 
Fe enhanced (4233-25, 4584-02). . . . J 
Majority of other arc lines. 
1-6 
— 
700 
— 
Carbon fluting 3883-55 and many other lines 
0-6 
1-05 
270 
475 
As I pointed out in connection with the eclipse of 1898, these results do not 
necessarily give the actual heights reached by the various vapours, as only the 
brightest low’er portions of the chromospheric arcs may be registered on the 
photographs. That the heights given in the table do not represent the upper limits 
of the respective vapours is indicated by measures which have been made of photo¬ 
graph No. 5, which had an exposure of 6 seconds; some of the arcs in this 
photograph are as long or longer than the corresponding ones in Nos. 1-4. Not¬ 
withstanding the less favourable position of the moon, correcting for the moon’s 
motion, the measured arcs in photograph No. 5, reduced to miles, are as follows :—- 
* ‘ Koy. Soo. Proc.,’ vol. 64, p. 87, 
•1 r- •*> 
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