Light of a Solar Protuberance. 87 
cannot be conceived as being due to the reflection of light, as 
in the case of the clouds in our atmosphere: it is the protuber- 
ance itself which is rendered luminous by some change taking 
place in it. These observations would seem to indicate that on 
the sun there are sometimes dark and non-luminous protuber- 
ances, which may cause the spots of absorption often observed 
in the vicinity of spots. 
The phenomenon of the gradual illumination of a protuber- 
ance was observed in 1869, at Des Moines, Iowa, during the 
total eclipse of the sun, by Professor William A. Rogers, who 
accompanied Dr. C. H. F. Peters, on the Litchfield Eclipse Ex. 
ition. Professor Rogers was observing a large protuber- 
ance on the sun with a 9-inch-aperture refractor, when he saw 
several protuberances form gradually in the vicinity of the 
large flame, and at a considerable height above the chromo- 
e 
ere. 
The projection of the hydrogen flames on the spectrum is 
not a very rare phenomenon during the period of maximum of 
sun-spots, and it has been observed several times. However, 
ei 
On Sept. 10th, 1872, at 125 33™, I was anaes smal] nar- 
row flame forming an arch on the chromosphere, the height of 
n 
Jike a rope. For a few seconds, it continued to ascend, at the 
same time growing wider; and at 12" 37™, it had attained its 
sunk to a level with the chromosphere and was lost in it. 
_ At the same instant that the are of hydrogen was distended, 
it was seen rojected on the spectrum opposite the sun, to- 
wards the violet. The figure of this protuberance appea 
exactly the same, whether it was projected on the spectrum or 
Seen between the wide-open jaws of the slit. However, when 
the slit was narrow, the flame became invisible on the C line, 
although it remained projected on the spectrum. When the 
protuberance, after having reached its greatest altitude, de- 
