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POPULAK SCIENCE REVIEW. 
which seemed to him ill-defined and imperfect, is the very 
image which Fr. Secchi finds most perfect when the open-slit 
method is employed on the uneclipsed sun. Xor is it difficult 
to understand why the indigo image should have appeared less 
perfect during Respighi’s eclipse observations than during 
Secchi’s researches in full daylight. For Respighi had the full 
light of the red and yellow images, as well as that of the less 
brilliant blue-green image, shining in the same field as the 
faint light of the indigo image, and therefore rendering his eye 
insensible to the feebler parts of this image. But when the 
open-slit method is employed in full daylight, the indigo image 
is observed under circumstances even more favourable than in 
the case of the red and orange-yellow images. F or the part of 
the atmospheric spectrum which then forms the background of 
the indigo image is the indigo part of that spectrum ; no red, 
yellow, or green light is admitted at all into the field of 
view. 
It is more important to notice the effect of glare or strong 
light in the field of view than might at first sight appear. For 
though no very great importance can be attached to what 
Respighi noticed respecting the prominences (save as illustrating 
his method of observation), yet we learn, from comparing what 
he saw with what is known about the prominences, to estimate 
the effect of light in obliterating the fainter portions of circum- 
solar appendages, and this is a matter of paramount importance 
in its relation to Respighi’s observations of the corona. 
Before passing to the corona, however, it will be well to 
notice that Mr. Lockyer also saw the prominences and chroma- 
tosphere separated into four coloured images. But the four 
colours mentioned by Mr. Lockyer were not the same as those 
mentioned by Respighi, and there seems reason for believing that 
the indigo image lay out side the field of Mr. Lockyer’s instrument, 
or else was too faint for recognition, while the extra image seen 
by Mr. Lockyer was not an image of the chromato sphere at all, 
but of the brighter part of the inner corona. The account first 
announcing Mr. Lockyer’s observations ran thus, “Four circles, 
1474 same size and faint,” and subsequent explanation revealed 
that he had seen four images of the chromatosphere, one red, 
one yellow, one yellow-green and faint, corresponding to Kirch- 
hofiPs 1474, and the fourth blue-green. The faint image did 
not appear to him to extend more than two minutes from the 
moon’s limb. 
Respighi was favoured with better success, however. “ The 
coloured zones of the corona became continually more strongly 
marked,” he says, 66 one in the red corresponding with the line 
C ; another in the green, probably coinciding with the line 1474 
of Kirchhoff ’s scale ; and the third in the blue, perhaps coin- 
