"The spectroscopic observations made by Mr. Huggins on the light of three comets show that a certain portion, at least, of the light of these objects is inherent. . . . The nucleus gave in each case three bands of light, indicating that the substances of the nuclei consisted of glowing vapor."[2]
In one case, the comet-head seemed, as in the case of the, comet examined by Padre Secchi, to consist of pure carbon.
In the great work of Dr. H. Schellen, of Cologne, annotated by Professor Huggins, we read:
"That the nucleus of a comet can not be in itself a dark and solid body, such as the planets are, is proved by its great transparency; but this does not preclude the possibility of its consisting of innumerable solid particles separated from one another, which, when illuminated by the sun, give, by the reflection of the solar light, the impression of a homogeneous mass. It has, therefore, been concluded that comets are either composed of a substance which, like gas in a state of extreme rarefaction, is perfectly transparent, or of small solid particles individually separated by intervening spaces through which the light of a star can pass without obstruction, and which, held together by mutual attraction, as well as by gravitation toward a denser central conglomeration, moves through space like a cloud of dust. In any case the connection lately noticed by Schiaparelli, between comets and meteoric
[1. "The Heavens," p. 239.
2. Note to Guillemin's "Heavens," p. 261.]
{p. 69}
showers, seems to necessitate the supposition that in many comets a similar aggregation of particles seems to exist."[1]
I can not better sum up the latest results of research than by giving Dr. Schellen's words in the work just cited:
"By collating these various phenomena, the conviction can scarcely be resisted that the nuclei of comets not only emit their own light, which is that of a glowing gas, but also, together with the coma and the tail, reflect the light of the sun. There seems nothing, therefore, to contradict the theory that the mass of a comet may be composed of minute solid bodies, kept apart one from another in the same way as the infinitesimal particles forming a cloud of dust or smoke are held loosely together, and that, as the comet approaches the sun, the most easily fusible constituents of these small bodies become wholly or partially vaporized, and in a condition of white heat overtake the remaining solid particles, and surround the nucleus in a self-luminous cloud of glowing vapor."[2]