446 METEORITES. [SECT, xxxvn. 



for aught we know, myriads of bodies may be wandering in 

 space unseen by us, of whose nature we can form no idea, 

 and still less of the part they perform in the economy of 

 the universe. Even in our own system, or at its farthest 

 limits, minute bodies may be revolving like the telescopic 

 planets, which are so small that their masses have hitherto 

 been inappreciable, and there may be many still smaller. 

 Nor is this an unwarranted presumption ; many such do 

 come within the sphere of the earth's attraction, are ignited 

 by the velocity with which they pass through the atmo- 

 sphere, and are precipitated with great violence on the 

 earth. The fall of meteoric stones is much more frequent 

 than is generally believed. Hardly a year passes without 

 some instances occurring ; and, if it be considered that only 

 a small part of the earth is inhabited, it may be presumed 

 that numbers fall in the ocean, or on the uninhabited part 

 of the land, unseen by man. They are sometimes of great 

 magnitude ; the volume of several has exceeded that of the 

 planet Ceres, which is about 70 miles in diameter. One 

 which passed within 25 miles of us was estimated to weigh 

 about 600,000 tons, and to move with a velocity of about 

 20 miles in a second ; a fragment of it alone reached the 

 earth. The obliquity of the descent of meteorites, the 

 peculiar substances they are composed of, and the explosion 

 accompanying their fall, show; that they are foreign to our 

 system. Luminous spots, altogether independent of the 

 phases, have occasionally appeared on the dark part of the 

 moon ; these have been ascribed to the light arising from 

 the eruption of volcanoes ; whence it has been supposed that 

 meteorites have been projected from the moon by the im- 

 petus of volcanic eruption. It has even been computed 

 that, if a stone were projected from the moon in a vertical 

 line, with an initial velocity of 10,992 feet in a second - 

 more than four times the velocity of a ball when first dis- 

 charged from a cannon instead of falling back to the 

 moon by the attraction of gravity, it would come within the 



