We therefore draw the conclusion that these messengers from other solar systems which bring us samples of their chemical elements are closely related to our sun and to the interior of our earth. That other stars and comets are essentially composed of the same elements as our sun and earth, spectrum analysis had already intimated to us. But various metalloids, like chlorine, bromine, sulphur, phosphorus, and arsenic, which are of importance for the composition of the earth, have so far not been traced in the spectra of the celestial bodies, nor in that of the sun. We find them in meteorites, however, and there is not the slightest doubt that we must likewise count them among the essential constituents of the sun and other celestial bodies. It is with difficulty, however, that the metalloids can be made to exhibit their spectra, and this is manifestly the reason why spectrum analysis has not yet succeeded in establishing their presence in the heavens. As regards the recently discovered so-called noble gases helium, argon, neon, krypton, and xenon, their presence in the chromosphere has been discovered on spectrograms taken during eclipses of the sun (Stassano). According to Mitchell, however, these statements would appear to be somewhat uncertain as to krypton and xenon. The small particles of dust which the radiation pressure drives out into space to all possible distances from the sun and the stars may hit against one another and may accumulate to larger or smaller aggregates in the shape of cosmical dust or meteorites. These aggregates will partly fall upon other stars, planets, comets, or moons, and partly—and this in very great multitudes—they will float about in space. There they may, together with the larger dark celestial bodies, form a kind of haze, which partly hides from us the light of distant celestial bodies. Hence we do not see the whole sky covered with luminous stars, which would be the case if, as we may surmise, the stars were uniformly distributed all through the infinite space of the universe, and if there were no obstacle to their emission of light. If there were no other celestial bodies of very low temperature and very large dimensions which absorbed the heat of the bright suns, the dark celestial bodies, the meteorites, and the dark cosmical dust would soon be so strongly heated by solar radiation that they would themselves turn incandescent, and the whole dome of the sky would appear to us like one glowing vault whose hot radiation down to the earth would soon burn every living thing.