TOTAL ECLIPSE OF THE SUN, APRIL 16, 1893. 
555 
differences as can be attributed to difference of phase. The dispersion was very 
small compared with the size of the sun’s image, so that the photographs present 
the appearance of an ordinary photograph of the eclipsed sun which is slightly 
distended in the direction of dispersion. The various prominences each show three 
images, two of which were identified with H^, H y , while the others were found to 
correspond to a wave length of about 3957. 
It was suggested (Report, p. 149) that this represented the H and K radiations of 
calcium, and this is fully confirmed by the results obtained in 1893, to say nothing 
of results obtained in other eclipses. 
In addition to the protuberances, the photographs show a well defined circular 
boundary of the moon’s limb at a position corresponding to H y . This was considered 
to be an indication that hydrogen was one of the substances existing in an incan¬ 
descent state in the corona itself, for although coronal rings corresponding to 
and H 5 were not photographed, their absence may possibly be accounted for by the 
fact that the plates employed were most sensitive to the H y region. 
There are also indications of a continuous spectrum from the lower parts of the 
corona, shown by well defined structure running parallel to the direction of 
dispersion. 
I next proceed to remark very briefly upon the photographic results obtained 
since 1875. 
In 1878, near the sun-spot minimum, the method was employed by several 
observers, myself among them, but no bright rings were recorded. The maximum 
sun-spot conditions previously observed had entirely changed ; indeed with a slit 
spectroscope the 1474 line was very feeble, and was only seen by a few of the 
observers, and hydrogen lines were similarly feeble.* 
Part of my own equipment for this eclipse consisted of a small grating placed in 
front of an ordinary portrait camera, and with this I obtained a photograph showing 
only a very distinct continuous spectrum.! 
The method was employed by Dr. Schuster in Egypt in 1882 ; the camera was of 
3 inches aperture and 20 inches focal length, with a prism having a refracting angle 
of 60°4 
The single photograph obtained (which was not reproduced) was stated to show 
two rings, which were considered to be due to the lower parts of the corona, and 
therefore to correspond to true coronal light. The wave-length of one of these rings 
was measured to be 5315 ; it is due to the green corona line (1474k). The second 
was stated to be coincident with D 3 . The ring in the green was particularly strong 
in the south-western quadrant, and hardly visible at some other points of the sun’s 
* ‘ American Journal of Science,’ vol. 16, p. 243. 
t With a duplicate grating I observed the spectrum of the eclipsed sun, and again in three different 
orders, saw nothing but continuous spectrum (‘ Nature,’ vol. 18, 1878, p. 459). 
t ‘ Phil. Trans.,’ vol. 175, 1884, p. 262. 
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