If the dust of thousands of meteorites is always thus falling earthward, one would imagine that it must in time add something to the weight of the earth. And this actually is the case. During the last three thousand years, no less than one million tons of meteorite-dust must, according to calculation, have fallen to earth out of the sky. A million tons is of course a mere nothing compared with the size of the world. Still, the fact is curious and interesting. It has been suggested that, _perhaps_ the flames of the sun are partly fed by vast showers of falling meteorites. It has even been suggested that _perhaps_, in long past ages, the earth and the planets grew to their present size under a tremendous downpour of meteorites; the numbers which now drop to earth being merely the thin remains of what once existed. But for this guess there is no real foundation. Whether suns and worlds full-grown, created as in an instant; whether tiny meteorites in countless myriads to be used as stones in “building;” whether vast masses of flaming gas, to be gradually cooled and “framed” into shape--which ever may have come first, and whichever may have been the order of God’s working--still that “first” was made by him; still he throughout was the Master-builder. [Illustration: GREAT COMET OF 1680.] A few words more about “comet-visitors.” Many comets, as already stated, belong to our Solar System, though whether they have always so belonged is another question. It is not impossible that they may once upon a time have wandered hence from a vast distance, and, being caught prisoner by the powerful attraction of Jupiter or one of his three great brother-planets, have been compelled thenceforth to travel in a closed pathway round the sun. [Illustration: GREAT COMET OF 1769.] There are also many comets which come once only to our system, flashing round past the sun, and rushing away in quite another direction, never to return. Where do these comets come from? And where do they go? From other suns--brother suns to ours? It may be. One is almost disposed to think that it must be so. Do we ever think what an immense voyage they must have made to come from there to here? Do we imagine for how many years they must have flown through the dark immensity to plunge themselves into the fires of our sun? If we take into account the directions from which certain comets come to us, and if we assign to the stars situated in that region the least distances consistent with known facts, we find that these comets certainly left their last star more than _twenty millions of years ago_.