TOTAL ECLIPSE OF THE SUN, APRIL 16, 1893. 
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was employed as a source of light, and it will be seen that although there was no 
suspicion of anything but continuous radiations, an appearance of rings was produced 
exactly resembling those to which reference has been made as taken during the eclipse. 
Interpretation of the Photographs taken out of Totality. 
The photographs taken out of totality greatly increase the chances of obtaining a 
record of the spectra of the vapours near the photosphere. It is evident that shallow 
strata can only be visible for a very short time after the beginning and before the end 
of totality, but they will be visible at the cusps out of totality, so long as the general 
illumination of the sky by the uneclipsed part of the photosphere is insufficient to 
mask them. 
Fig. 15. 
General explanation of photographs taken out cf totality. 
Fig. 15 will facilitate a general explanation of the jffiotographs taken out of totality. 
The part of the diagram to the left represents the relative positions of the sun and 
moon at the African station about a minute after totality, there being a thin crescent 
of photosphere then visible in the south-west quadrant. Two imaginary layers of 
vapour are drawn round the sun. The direction of dispersion being north and south, 
the spectrum is drawn out in the direction indicated by the continuous spectrum in 
the part of the diagram on the right. It is evident that the radiations of the outer 
layer of vapour will be represented by long arcs in the spectrum of the cusp, while 
those proceeding from the lower vapour will be represented by shorter ones. 
It may be remarked also that the lengths of the arcs at the cusps for any particular 
layer of vapour will depend upon the interval from totality at which the photograph is 
taken ; even a shallow layer will be represented by long spectrum arcs at the moments 
