30 Fietp CotumBiAN MusrumM—GEo oey, VOL. 1. 
at these intervals. It had previously been seen in 1772 and 1805 and 
returned to the solar system in due order in 1832. Being in an un- 
favorable position in 1839 it could not be seen, but at the time of its 
next appearance in 1846 it was found to have separated into two por- 
tions, which kept drifting farther apart during the time in which the 
comet remained visible. At its next appearance in 1852, the frag- 
ments were seen to be smaller and still more widely separated. In 
accordance with its times of revolution the comet should have reap- 
peared in 1859, 1866, 1872, 1879 and 1885, but though carefully 
looked for, it has never been seen again. 
On November 27, 1872, however, occured a meteoric shower 
extraordinary for the number and brilliancy of the meteors which 
flashed through the air. The orbit of these proved to be exactly that 
of Biela’s comet. On the same date in 1885 occurred another remark- 
able shower of meteors, having the same orbit and radiant point as 
those of 1872. During this shower an iron meteorite weighing about _ 
8 pounds fell at Mazapil in Mexico. The manifest conclusion, there- 
fore, 1s that sometime between the years 1852 and 1872, Biela’s comet 
was shattered in pieces and some of these meteors were the resulting 
fragments. These fragments being small, were mostly burned up 
in their passage through the upper part of the earth’s atmosphere, 
but had they been larger, numbers of meteorites would probably 
have fallen to the earth. 
The fact, however,that so few meteorites have fallen to the earth 
during the star showers has been urged by some authorities as proof 
that the meteors producing stones are of a different nature from those 
which we see only as shooting stars. Since however, every grada- 
tion may be traced from one to the other and astronomically they are 
all alike, there is little reason, in the view of many authorities, to 
doubt their similarity. 
Attention has already been called to the fact that though upon 
the earth’s surface iron is rarely found uncombined, there are masses 
found in the basalt of Greenland which are altogether metallic and 
which in composition and structure closely resemble the meteoric 
irons. Though other views as to their origin have been advanced, 
many facts point to the conclusion that these iron masses have been 
brought up with the basalt and therefore indicate the existence of 
metal of this character in the deep interior of the earth. It has long 
been known that the matter constituting the interior of the earth 
must be more dense than that of the rocks which form its crust, since 
the specific gravity of the earth as a whole is 5.5, while that of the 
rocks of the crust is not more than 2.7. Professor Dana has shown 
