TOTAL ECLIPSE OF THE SUN, xVPRIL 16, 1893. 
601 
Determination of Intensities. 
The scale of intensities which has been adopted is such that 10 represents the 
brightest lines and 1 the faintest. This will facilitate comparisons with Young’s 
well-known list of chromospheric lines, in which 100 represents the maximum 
frequency and brightness. The intensities have been estimated by taking the 
strongest line in each negative as 10, irrespective of length of exposure. 
Table I. gives the intensities of the various lines as they appear in different 
photographs of prominences Nos. 3 and 19, and in the spectrum of the cusp a 
few seconds after totality. The intensities of the lines in different photographs 
of the spectrum of another prominence, No. 13, are shown in Table II., and those at 
the outside of the chromosphere are contrasted with the intensities of the same lines 
at the base in Table III. 
XI. Loci of Absorption in the Solar Atmosphere. 
The Spectra of Prominences and Chromosphere at Different Heights. 
If we consider a prominence on that part of the sun’s limb where the second 
contact takes place, the first photograph taken during totality will show the spectrum 
of the whole prominence, and succeeding photographs will give the spectrum of the 
same prominence with the lower parts gradually cut off by the moon’s edge. In the 
case of a prominence at the opposite limb, similar sections will be represented in 
successive photographs, and the last photograph taken during totality will show the 
spectrum of the greatest part of the prominence. 
Prominences Nos. 3 and 19 (see fig. 10) have been investigated in this way, and 
particulars of their spectra at various heights are recorded in Table I. The first of 
them is shown in the African Photographs Nos. 7 to 13 inclusive, and the latter in 
Photographs 19 to 21 inclusive. The height above the ohotosphere, reckoned in 
seconds of arc, and in miles, at which each spectrum is given, is indicated beneath the 
numbers of the photograph in which the prominences appear. The relative intensities 
of the lines at different heights are shown by the figures ranged in horizontal lines 
with the wave-lengths. Some of the lines remain of the same relative intensity 
throughout all parts of the same prominence; others again dim rapidly in passing 
towards the upper parts. The two prominences in question are also seen to behave 
differently in respect to some of the lines ; thus the line at a 3856*5 disappears before 
a height of 2,000 miles is reached in prominence No. 3, but remains visible at a height 
of over 4,000 miles in prominence No. 19. Lines also occur in one prominence which 
do not appear in the other, e.g ., X 4313*2. Other differences are also revealed by the 
table, but it may be remarked that too much stress should not be laid on the presence 
or absence of the very faintest lines in some of the photographs, as variations may 
be partially attributed to differences in the quality of the photographs. 
MDCCCXCVI.—A. 4 H 
