Interior of the Earth

Parts
of the
radius.     Density.
0.0        11.0
0.1        10.3
0.2         9.6
0.3         8.9
0.4         8.3
0.5         7.8
0.6         7.4
0.7         7.1
0.8         6.2
0.9         5.0
1.0         2.6

[Illustration]

Twice a year, said Professor Dewar, what are called “falling stars” maybe plentifully seen; the times of their appearance are in August and November.  Although thousands upon thousands of such small meteors have passed through our atmosphere, there is no distinct record of one having ever fallen to the earth during these annual displays.  One was said to have fallen recently at Naples, but on investigation it turned out to be a myth.  These annual meteors in the upper air are supposed to be only small ones, and to be dissipated into dust and vapor at the time of their sudden heating; so numerous are they that 40,000 have been counted in one evening, and an exceptionally great display comes about once in 331/4 years.  The inference from their periodicity is, that they are small bodies moving round the sun in orbits of their own, and that whenever the earth crosses their orbits, thereby getting into their path, a splendid display of meteors results.  A second display, a year later, usually follows the exceptionally great display just mentioned, consequently the train of meteors is of great length.  Some of these meteors just enter the atmosphere of the earth, then pass out again forever, with their direction of motion altered by the influence of the attraction of the earth.  He here called attention to the accompanying diagram of the orbits of meteors.

The lecturer next invited attention to a hollow globe of linen or some light material; it was about 2 ft. or 2 ft. 6 in. in diameter, and contained hidden within it the great electro-magnet, weighing 2 cwt., so often used by Faraday in his experiments.  He also exhibited a ball made partly of thin iron; the globe represented the earth, for the purposes of the experiment, and the ball a meteorite of somewhat large relative size.  The ball was then discharged at the globe from a little catapult; sometimes the globe attracted the ball to its surface, and held it there, sometimes it missed it, but altered its curve of motion through the air.  So was it, said the lecturer, with meteorites when they neared the earth.  Photographs from drawings, by Professor A. Herschel, of the paths of meteors as seen by night were projected on the screen; they all seemed to emanate from one radiant point, which, said the lecturer, is a proof that their motions are parallel to each other; the parallel lines seem to draw to a point at the greatest distance, for the same reason that the rails of a straight line of railway seem to come from a distant central point.  The most interesting thing about the path of a company of meteors is, that a comet is known to move in the same orbit; the comet heads the procession, the meteors follow, and they are therefore, in all probability, parts of comets, although everything about these difficult matters cannot as yet be entirely explained; enough, however, is known to give foundation for the assumption that meteorites and comets are not very dissimilar.