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XII. Solar Eclipse of 1900, May 28 .—General Discussion of Spectroscopic 
Results. 
By J. Evershed, F.R.A.S. 
Communicated hy the Joint Permanent Eclipse Committee. 
Received December 17, 1902,—Read January 22, 1903. 
[Plates 2 , 3.] 
In the preliminary report of an expedition to the south limit of totality, in Algeria, I 
described in detail the methods adopted and the instruments employed in obtaining 
photographs of the “flash” spectrum in high solar latitudes.* 
The jiresent paper deals with the results obtained from a detailed study and 
measurement of four of the best negatives of the series of sixteen which were secured 
with the principal instrument, a reflecting prismatic camera. 
This instrument was an ordinary reflecting telescope of 188 centims. focus, fitted 
with two prisms of light flint glass at the upper end of the tube near the position 
usually occupied by the small mirror of the Newtonian reflector. The prisms had an 
eflective ajierture of 8 centims. and angles of 60° and 45° respectively; they were set 
approximately at minimum deviation for K, and gave a linear dispersion at the focus 
of the large mirror equal to 93 millims. between F and K. 
Description of the Photographs. 
The plates were exposed near the time of greatest phase of the eclipse, which was 
not quite total at my station. The first plate was exposed at 45 seconds before, and 
the last at 32 seconds after, the computed time of mid-eclipse. Owing to the position 
of my station, near the extreme limit of the zone of total-eclipse, and just outside that 
limit, there appears in all the photographs a considerable amount of continuous 
spectrum due to the uneclipsed photosphere. Notwithstanding this, all the exposures 
which were made within 15 seconds of mid-eclipse yielded good images of the flash 
spectrum, and the sky illumination was sufficiently reduced to allow of the fainter 
* ‘Roy. Soc. Proc.,’ vol. 67, p. 370. 
VOL. CCI.— A 342. 3 N 15.7.03 
