TOTAL ECLIPSE OF THE SUH, APRIL 16, 1893. 
575 
From the points of maximum photographic action the continuous spectrum 
diminishes in height and intensity in both directions. 
The 1474 ring appears on Photographs 9, 16, 17, and 18, the last three being 
isochromatic; its appearance on Photograph No. 9 indicates its great intensity in the 
lower corona. It is important to bear in mind that in successive photographs the 
conditions are different. Thus Photograph 9 was exposed between 18 and 23 seconds 
after the commencement of totality, so that at the beginning of the exposure the 
lowest part of the corona, in the north-east quadrant, was only about 3,000 miles 
from the photosphere, the relative movement of the moon when projected on the sun 
being about 166 miles per second. At the beginning of the exposure of Photograph 
16, on the other hand, the lowest part of the corona photographed in the north-east 
quadrant was nearly 24,000 miles above the photosphere, and that in the south-west 
quadrant about 18,000 miles; in this photograph the 1474 ring is consequently 
brightest in the south-west quadrant. In the case of Photograph No. 17 the 
conditions at the beginning of the exposure were almost identical with those at the 
end of No. 16, but in this case the exposure was 40 seconds; at the middle of the 
exposure the moon’s limb would be about 27,000 miles above the photosphere in the 
north-east quadrant, and in the south-west nearly 15,000 miles. 
At the middle of the exposure of Photograph No. 18, the corresponding figures 
were about 31,000 and 11,000 miles. 
The greatest height of the 1474 K ring occurs in No. 17, taken with a long 
exposure; in its brightest part it extends about 45" above the moon’s limb, corre¬ 
sponding to a distance of about 20,000 miles. Its intensity varies greatly, being 
scarcely visible in the region of the sun’s poles, and brightest in the equatorial 
regions ; the brightest parts of the ring correspond with the brightest regions in the 
photographs of the corona taken with the coronagrapli. The ring is quite distinct 
from the prominence rings and is not intensified in the region of prominences, indeed 
there seems to be no trace of 1474 in the spectrum of any of the prominences. 
In Negative No. 17, Plate 12, the 1474 ring is at the right of the photograph, just 
within the very broad ill-defined ring due, as shown elsewhere, to photographic 
causes. 
Like 1474 K, the fainter coronal rings are as readily distinguished from chromo¬ 
sphere and prominence rings, as the latter are from the corona in an ordinary 
photograph, as their maximum luminosity never coincides with them; while the 
monochromatic images of chromosphere and prominences are sharply outlined, the 
true coronal rings are not thus defined. The intensities of the coronal radiations 
appear to diminish very rapidly in passing outwards from the sun’s limb. The dis¬ 
tribution of these rings in the African Negative No. 17 is shown by the dotted arcs 
in Plate 12, it being quite impossible to reproduce the rings themselves in photo¬ 
graphic enlargements in consequence of their dimness. 
