Ragnarok : the age of fire and gravel

WHAT IS A COMET? 69

oric showers, seems to necessitate the supposition that in many comets a similar aggregation of particles seems to exist.” *

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.” +

Here, then, we have the comet :

First, a more or less solid nucleus, on fire, blazing, glowing.

Second, vast masses of gas heated to a white heat and enveloping the nucleus, and constituting the luminous head, which was in one case fifty times as large as the moon,

Third, solid materials, constituting the tail (possibly the nucleus also), which are ponderable, which reflect the sun’s light, and are carried along under the influence of the nucleus of the comet.

Fourth, possibly in the rear of all these, attenuated volumes of gas, prolonging the tail for great distances.

What are these solid materials ?

* “Spectrum Analysis,” 1872. + Ibid., p. 402.