262 
source for research material. This col- 
lection is important not only because 
of its size and completeness, but also 
because all the meteorites in it have 
been studied and the information thus 
obtained has been classified. Over 100 
different publications have been issued 
describing meteoritic material on de- 
posit in the Museum. 
The first publication of the National 
Museum relating to meteorites ap- 
peared in 1888, when Dr. George P. 
Merrill published a description of the 
stone from Bluff, Tex. The next to be 
issued, in 1894, was the description of 
the stone from Beaver Creek, British 
Columbia. The growth and import- 
ance of the collection are largely due 
to the lifetime work of Dr. Merrill. He 
described 65 different falls and also 
published several general papers on 
the structure and composition of 
meteorites. 
The Museum also maintains a 
catalog of all known metoritic mate- 
rial of the world. The foreign meteor- 
ites are listed under the countries in 
which they have been found; those 
from the United States are listed under 
their respective States and also by the 
latitude and longitude of the place of 
their discovery, so that when new 
material comes in, it can be proved to 
be either a new fall or part of an old, 
well-known one. 
An extensive metallographic study 
has been made of the iron meteorites, 
and 1,933 microphotographs, each 
with its metallographic description, 
have been made of 144 different 
meteorites. ‘This represents the work 
of Stuart H. Perry, associate in min- 
eralogy, who has carried on this study 
for many years. 
How To Recognize a Meteorite 
The physical features of a meteorite- 
are sufficiently constant so that after 
one has seen several or carefully exame 
ined good illustrations of them, thc 
identification of a possible meteoritie 
specimen should be reasonably simpls 
and accurate. The specific test 
needed to determine the meteoritic 
ANNUAL REPORT SMITHSONIAN INSTITUTION, 1948 
nature of either a stone or an iron 
should be performed by someone who 
is familiar with them, as now and then 
unusual specimens are found, the 
analysis of which requires a trained 
worker. 
The external portions of both stony 
and iron meteorites show evidence of 
their struggle to penetrate our at- 
mosphere. The outer portion of a 
fallen meteorite is covered with a thin 
crust of fused material (pl. 1, 3). 
Sometimes stones and irons are frag- 
mented before the end of their flight 
and then their surfaces are not entirely 
covered with fused material. Stony 
meteorites are sometimes so friable, 
or loosely bonded together, that they 
may break apart on striking the earth. 
Iron meteorites have been found with 
small areas of their surface broken off 
toward the end of the flight. It has 
already been noted that our largest 
meteorites are metallic, apparently for 
the reason that they are less likely to 
break apart on falling than the stony 
varieties. 
During the few seconds in which a 
falling meteorite has a high velocity, 
the frictional heat generated by the air 
resistance causes the outermost crust 
to fuse. This film of fused material 
can never become very thick (pl. 1, 
b), because the air friction erodes the 
material away as it forms. Thus the 
crust found on a meteorite is the 
material that fused probably not very 
far above the surface of the earth. 
It is a surprise to many people to 
learn that meteorites are not masses of 
fused molten material. The centers of 
these objects show no indication of 
having been very hot during their fall. 
In fact most of the heat noticed on 
collecting a freshly fallen meteorite is 
believed to be heat that results from 
the impact of the object with the 
ground. Some of the freshly fallen 
American meteorites have been notice- 
ably cold to the touch when recovered 
immediately after their fall. The 62)- 
pound stone which fell near Allegan, 
Mich., was recovered within a few 
moments after its fall, and the sand 
