Such comets, however, are rare, and in ancient and medieval times comets were always regarded with terror--as an evil omen--and at times the people believed that they foretold the end of the world, causing veritable panics, like the “comet scare” of France in 1832. As a rule these comets reappear at intervals, such as do Halley’s, Euke’s and Donati’s comets. They travel at a tremendous speed, coming at times quite close to the earth. Quite often they cross the path of the earth, causing fear that a collision might take place. There are a few isolated cases of comets colliding with the earth and killing a few people. Some of the comets have been lost, that is we do not know what became of them. Such a lost wanderer of the skies is Biela’s comet; a comet of some forty thousand miles diameter. In its appearances, every sixth and sixteenth year, its course would come within a few thousand miles of the earth’s orbit. Besides the luminous clouds we see in the heavens and which, under the telescope are shown to be but great groups of separate stars, there are others which no telescopic power has as yet been able to disclose individually. These are known as nebulae and are of varying shape and form and very beautiful in appearance. Once in a while the earth passes through such a nebulae. Some years ago the Heidelberg Observatory reported that the earth was passing through some such nebulae, which report was confirmed by various other observatories. In that case there was no noticeable effect on human life, but it is believed by astronomers that some of these nebulae are composed of strong poisonous gases and that if ever the earth passes through such a nebulae all life on this planet will be destroyed. Occasionally bodies fall upon the earth out of the sky. These are the meteors. They are not noticeable until they come within our air zone, when the friction between them and the air causes them to become red hot, often being entirely consumed by the heat before reaching the earth itself. They travel through the air zone at a speed ranging from ten to forty miles per second, accompanied by a heavy continuous roar, emphasized now and then by violent detonations. These meteors are solid bodies; containing a large percentage of iron and copper and single pieces have been found to weigh as much as seventy-five thousand pounds.