OF SOME OE THE STARS AND NEBULAE. 
555 
beneath the photosphere, similar to those which exist in the less normal phenomenon of 
sun-spots. 
Mr. Lockyer’s observations and my own would seem to show that probably no con- 
siderable part of the light which emanates from the umbra of a spot is due to luminous 
gas. It does not appear to me that this negative evidence is of great weight as to the 
complete absence of light in the umbra from such a source. The luminous gas would 
almost certainly emit light of the same refrangibility as some of the dark lines of the 
solar spectrum ; and if there existed above the spot the vapours of the same substances in 
a cooler state, the light might be wholly absorbed, and the feebler emanations of the 
still luminous but cooler vapours might not do more than render somewhat less intense 
the dark gaps produced by the vapours in the stronger light of all refrangibilities which 
is evidently present. 
What may be the source of the light which gives the continuous spectrum of the umbra 
we know not. It is not impossible that the dense and intensely heated gases which pro- 
bably form the inner substance of the sun, may in some cases emit lines so greatly 
expanded as to form, when numerous spectra are superposed, a sensibly continuous 
spectrum. In addition to this consideration, Dr. B. Stewart has suggested that, as gases 
possess a power of general absorption of light, a heated mass of gas if sufficiently dense to be 
opake, or partly so, would give a continuous spectrum as well as the spectrum of bright 
lines peculiar to it. It may be that, notwithstanding the high temperature, some sub- 
stances may exist in the liquid state in consequence of the pressure produced by the sun’s 
mass. 
§ VI. Observations of Comet II., 1868. 
Beceived July 2, 1868. 
On June 13 a comet was discovered by Dr. Winnecke, and also independently the 
same night by M. Becquet, Assistant Astronomer at the Observatory of Marseilles. 
I was prevented by buildings existing near my observatory from making observations 
of this comet before June 22. On that evening the comet was much brighter than 
Brorsen’s comet, a description of the spectrum of which I recently presented to the 
Royal Society*, and it gave a spectrum sufficiently distinct for measurement and com- 
parison with the spectra of terrestrial substances. 
Telescopic appearance of the Comet . — A representation of the comet as it appeared on 
June 22 at 11 p.m. is given in fig. 1, Plate XXXIII. The comet consisted of a nearly 
circular coma, which became rather suddenly brighter towards the centre, where there 
was a nearly round spot of light. The diameter of the coma, including the exterior faint 
nebulosity, was about 6' 20". The tail, which was traced for more than a degree, 
was sharply defined on the following edge, but faded so gradually away on the opposite 
side that no limit could be perceived. No connexion was traced between the tail and 
** Proceedings of the Eoyal Society, vol. xvi. p. 386. 
