Page:Popular Science Monthly Volume 29.djvu/761

Rh active, and that when they were active they were more likely to have been open seas of lava, not well fitted to shoot out such masses, the idea of the lunar origin of the meteorites gradually lost ground. But the unity of meteorites with shooting-stars, if true, increases a hundred-fold the difficulty, and would require that the comets have the same origin with the meteorites. No one claims that the comets came from the moon.

That the meteorites came from the earth's volcanoes is still maintained by some men of science, particularly by the distinguished astronomer royal for Ireland. The difficulties of the hypothesis are, however, exceedingly great. In the first place, the meteorites are not like terrestrial rocks. Some minerals in them are like minerals in our rocks. Some irons are like the Greenland terrestrial irons. But no rock in the earth has been yet found that would be mistaken for a meteorite of any one of the two or three hundred known stone-falls. The meteorites resemble the deep terrestrial rocks in some particulars, it is true, but the two are also thoroughly unlike. The terrestrial volcanoes must also have been wonderfully active to have sent out such a multitude of meteorites as will explain the number of stone-falls which we know and which we have good reason to believe have occurred. The volcanoes must also have been wonderfully potent. The meteorites come to us with planetary velocities. In traversing the thin upper air they are burned and broken by the resisting medium. Long before they have gone through the tenth part of the atmosphere, the meteorites usually are arrested and fall to the ground. If these bodies are sent out from the earth's volcanoes, they left the upper air with the same velocity with which they now return to it. This the law of gravitation demands. What energy must have been given to the meteorite before it left the volcano to make it traverse the whole of our atmosphere and go away from the earth with a planetary velocity! Is it reasonable to believe that volcanoes were ever so potent, or that the meteorites would have survived such a journey?

No one claims that the meteors of the star-showers, nor that their accompanying comets, came from the earth's volcanoes. To ascribe a terrestrial origin to meteorites is, then, to deny the relationship of the shooting-star and the stone-meteor. Every reason for their likeness is an argument against the terrestrial origin of the stones.

To suppose that meteors came from any planets that have atmospheres involves difficulties not unlike to and equally serious with those of a terrestrial origin. The solar origin of meteorites has been seriously urged and deserves a serious answer. The first difficulty which this hypothesis meets is that solid bodies should come from the hot sun. Besides this, they must have passed without destruction through an atmosphere of immense thickness, and must have left the sun with an immense velocity. Then there is a geometric difficulty. The meteorite shot out from the sun would travel under the law of gravitation