584 
MR, J. NORMAN LOCKYER ON THE 
these circles would overlap or not, according to the dispersive power of the prism and 
the difference in refrangibility of the lines. ... If the corona gives a series of bright 
lines we shall lind a series of outlines on the photographs similar to that corresponding 
to the protuberances. ... If we find that part of the corona gives a continuous 
spectrum, that part alone will be drawn out into a band.” 
To this it may be added, that successive photographs will differ on account of the 
difference of phase. One part of the chromosphere will be visible at the beginning of 
totality, and another part at the end. The smaller prominences visible at the 
beginning of totality are subsequently eclipsed by the moon, and their spectra 
are consequently absent from later photographs, while a new prominence region makes 
its appearance. In the same way, the part of the corona the spectrum of which is 
photographed will vary at different phases, but only in the lower parts. 
Corona. 
For the discussion of the advantages of the different methods of work in the case of 
the corona, it is necessary to consider the possible sources of spectra which are to be 
found in the neighbourhood of the corona. From previous experience, the chief 
sources may be stated as follows :— 
(a) Intrinsic light of the corona, giving the so-called continuous spectrum. 
(b) Intrinsic light of the corona, giving bright lines. 
(c) Light of the sun reflected by the solid or liquid particles in the corona. 
(cl) Light scattered by the particles in our own atmosphere, giving frequently the 
lines of the chromosphere and prominences. 
It is evident that a slit spectroscope must integrate all these spectra, so that in 
discussing any particular line it is very difficult to know to which origin it should 
be ascribed. For example, if we suppose the corona to give a spectrum of hydrogen, 
the lines will be superposed upon lines of hydrogen due to the light of the prominences 
scattered by our atmosphere, and it would not be safe to draw any conclusion as to 
the presence or absence of hydrogen in the corona. 
The advantages of the slit spectroscope in regard to the corona may be stated as 
follows :— 
(1.) If the spectrum of the corona consists of a large number of lines of nearly 
equal intensity, the slit spectroscope will show them more clearly than the prismatic 
camera, for the reason that, with the latter instrument, the overlapping of the rings 
would have a greater tendency to give the spectrum the appearance of being con¬ 
tinuous. With a wide slit this advantage of the slit spectroscope would be 
diminished. 
(2.) Feeble corona lines have a greater chance to show themselves with the slit 
spectroscope, since it only takes account of a very small area giving continuous 
spectrum, while, in the prismatic camera, the continuous spectrum from adjacent 
