434 ME. J. N. lockyee on specteoscopic obseevatiqns oe the SUN. 
repeated several times have failed to detect it. Were it a broad band having the same 
total amount of light, it would be invisible in the spectroscope ; it has probably there- 
fore reached this stage. 
III. The prominences have been observed of various colours (this fact is not here 
stated merely with reference to the observation recorded in III. ante). 
IV. There is a line in the yellow , most probably proceeding from the substance which 
gives off the light at C and F, as the length of this line, as far as the later observations 
with the more correctly adjusted instrument go, is the same as that of those in C and F. 
I am aware that the conditions as to density cannot for one moment be held to be the 
same in the two cases ; but as at present (so far as I know) we have no similar expe- 
riments ranging over greatly varying densities, I have thought it desirable to bring these 
striking facts forward at once. We are justified in thinking that the density of the 
chromosphere, always assuming that it is composed wholly or in part of hydrogen, can- 
not be very great ; if it were, the spectrum would most probably be continuous ; for Pro- 
fessor Frankland has shown, in the lecture before alluded to, that hydrogen burning in 
oxygen under a pressure of ten atmospheres gives out a spectrum, bright, and perfectly 
continuous from red to violet. 
It is possible that experiments in which both density and temperature are varied may 
enable us to match accurately the spectrum of the chromosphere, and thereby determine 
both the temperature and pressure at the surface of the sun. 
The bright lines which have been observed in several stars, especially in the remark- 
able one in Corona, the outburst of which was spectroscopically watched by Mr. Huggins 
in 1866, shows us that under certain conditions of constitution a chromosphere may be 
a part of the regular star-economy, and be liable to changes more or less great, and 
effected with more or less rapidity. The continuous observation of the sun’s chro- 
mosphere may therefore lead to a knowledge of many important facts. 
It is remarkable that in the outburst in the star in Corona, two of the lines of the 
chromosphere were coincident with C and F, and that two other lines were visible. If, 
therefore, either or both of these lines be due to hydrogen, we must regard that star, 
leaving the density of the envelope out of consideration, as being of lower temperature 
than our sun. 
The position of the prominences in all parts of the sun’s limb has generally been held 
to be sufficient evidence that they are not connected with spots. They may, however, 
still result from some common cause. It may be noted that* the eclipse which was pho- 
tographed by Mr. De La Hue in Spain happened near the time of maximum sun-spots, 
and that nearly the whole limb of the sun was covered with prominences. My observa- 
tions since 1866 have been carried on at the minimum sun-spot period, and the promi- 
nences observed during the eclipse this year were few in number, and covered but a 
small part of the sun’s limb. 
