Nature of the so-called Elements. 111 
ear :— 
“ During the first part of the eclipse two strong protuber- 
ances close together are noticed ; on the limb towards the end 
these are partially covered, while a series of protuberances 
came out at the other edge. The strongest of these protuber- 
ances are repeated three times, an effect of course of the prism, 
and we shall have to decide if possible the wave-lengths corre- 
sponding to the images. We expect a priori to find the hydro- 
gen lines represented. We know three photographic hydrogen 
Jines: F, a line near G, and A. F is just at the limit of the 
photographic part of the spectrum, and we find indeed images 
of protuberances towards the less refrangible part at the limit 
of photographic effect. For, as we shall show, a continuous 
Spectrum in the lower parts of the corona has been recorded, 
and the extent of this continuous spectrum gives us an idea 
of the part of the spectrum in which each protuberance line is 
placed. We are justified in assuming, therefore, as a prelimin- 
ary hypothesis, that the least refrangible line in the protuber- 
ance shown on the photograph is due to F, and we shail find 
support of this view in the other lines. In order to determine 
the position of the next line the dispersive power of the prism 
was investigated. The prism was placed on a goniometer table 
In minimum deviation for F, and the angular distance between 
F and the hydrogen line near G, i. e. Hy, was found, as a mean 
of several measurements to be 3’. The goniometer was gradu- 
ated to 15”, and owing to the small dispersive power, and 
therefore relatively great breadth of the slit, the measurement 
can only be regarded as a first approximation. ‘Turning now 
again to our photographs, and calculating the angular distance 
between the first atid second ring of protuberances, we find 
that distance to be 3’ 15”. We conclude, therefore, that this 
second ring is due to hydrogen. We, therefore, naturally 
looked for the third photographie hydrogen line, which is gen- 
erally called A, but we found no protuberance on our pho 
graphs corresponding to that wave-length. Although this line 
1s always weaker than Hy, its absence on the photograph is 
rather surprising, if it be not due to the fact that the line is 
one which only comes out at a high temperature. This is ren- 
dered likely by the researches of Frankland and Lockyer 
(Proc. Roy. Soc., vol. xvii, p. 453). 
