MR. J. N. LOCKYER ON SPECTROSCOPIC OBSERVATIONS OP THE SUN. 429 
is laid down from the mean of three careful micrometrical measurements made under far 
from good atmospheric conditions on the 15th of November. In Kirchhoff’s map the 
new line falls in a region where no line was measured by him. I may also add that, by 
the kindness of Mr. Gassiot, I have been enabled to inspect the very elaborate maps 
of the spectrum constructed at Kew Observatory. The measures above given make the 
new line fall between two lines of almost inconceivable faintness ; in Mr. Gassiot’s map, 
indeed, there are none but such lines for some distance on either side of the region in 
which the new one falls. 
On the 8th of November the existence of another line was definitely established ; its 
position in the spectrum is slightly less refrangible than Fraunhofer’s C. 
Unlike the other lines, which are seen in all prominences, this line is only visible at 
times, being rendered so apparently by the presence of certain conditions which are not 
permanent. Intense action going on in a prominence will sometimes render this line 
visible ; I am not, however, prepared to say that this is always the case. The line when 
visible is much more variable than the others ; at times it is the mere ghost of a line, at 
others it rivals the C line in brilliancy. 
Of the three lines C is generally more brilliant than F ; but I should add that it is 
difficult to determine the relative brilliancy of the lines because they are never seen 
together in the field of view of my instrument. The relative brilliancy of the line near 
D I am not sure about, because its situation in the brightest portion of the spectrum not 
only renders comparison difficult, but renders any conclusion which may be formed little 
worthy of confidence. My observations so far (November 16th) induce me to ascribe 
great variability, not only to the absolute, but to the relative, brightness of the lines. 
One instance is of the utmost importance. On the 5th of November, in sweeping round 
the sun with the F line in the field of view, I came across a prominence in which action 
of the intensest kind was evidently going on ; the light and colour of the F line were 
most vivid, the luminosity of the line was greater than that of any part of the solar 
spectrum then visible in the field (Plate XXXVII. fig. 4). The action was not general, 
but limited to certain points, as if the prominences were built up of clouds, and the 
action was intensest at their centres ; where the light was most vivid the spectrum 
widened out to almost the same extent as at the base*. The C line exhibited all the 
variations of brightness, but they were unaccompanied by any very decided widening of 
the line. The spectrum was too bright to observe the effect on the line near D. 
On the Dimensions and Forms of the Prominences. 
The prominence first observed on October 20th on the (true) southern limb of the 
sun was an exceedingly fine one ; its shape, as determined by sweeping the slit over it, 
was as represented in Plate XXXVII. fig. 7 ; its apparent height was about 3'. I 
did not stop to measure it more accurately. This prominence was not so visible on the 
next day of observation (the 22nd), as the sun’s rotation had carried it on to the disk. 
* This might have been an effect of mediation, hut I can scarcely think so. 
