I told you the air we breathe was made up of these two airs or gases; and it is. But many other gases sometimes float in it. One of these is hydrogen. It is produced in various ways, and is one of the most inflammable substances in the world. Now electricity, (or lightning, for it is the same thing) which is a subtle or penetrating fluid, always exists in the atmosphere, and has at all times power to ignite (set on fire) a vapor so inflammable as hydrogen, if it happens to come in contact with it. Now, again, as this hydrogen gas is most readily produced by the decomposition of water, and combines or mixes with various other matters arising from decaying vegetation, putrifying animal substances, in low and marshy swamps, a tiny spark is sufficient to ignite these combined gases, and thus set off the Will-o’-the-Wisps. THE AEROLITES. Stones falling—Where they come from—Arrival at the river Orinoco. Well, I extricated myself from the quagmire and returned,—though not without some difficulty, I had wandered so far, to my roosting place. The next morning as I was preparing to descend the tree, the sky being clear, and the sun shining, I was alarmed by a hissing noise in the air; and looking quickly around, I was just in time to see an immense mass of something, I could not tell what, falling from above, with a loud noise, and crushing in its fall, the branches of a lofty tamarind tree. Hastening to the spot, I found, to my surprise, an enormous piece of metal, quite hot, which had fallen with such force that it lay half buried in the swampy ground. I stood lost in wonder. When I was a boy, I had often picked up lumps of metal on the Wiltshire Downs, in England, but though told they were aerolites, I did not at that time believe a word of it. “Can the thin pure air,” thought I then, “form such hard bodies? Or can there be great iron mountains, and forges, and blacksmiths, and every thing of that sort, up in the air?” But now a huge mass lay at my feet. I had seen it fall. It was still hot. The boughs of the tamarind tree lay scattered about in every direction. How could I doubt any longer? Was it reasonable to deny facts, before my eyes, because I could not account for them? Do you wish to know if I can account for them _now_? Not a whit better. The moon, some say, has volcanic mountains which throw them out. But I don’t believe it. Think what an immense force of pressure it must take to send up a huge stone from one of our volcanoes, quite beyond the sphere of the earth’s attraction, so as to be met by the attraction of the moon and be carried to it! Do you believe such a thing could ever happen?