Year: 1877

readers to form general idea Of the re-
lations of our visitor, and similar bodies,
to the world on which we dwell.


The circle, OF about Ia inches in di-
ameter, represents the earth's orbit.
The arrows indicate the direction OF her
movement, the north pole being above
the plane OF the paper. The ellipse
represents the path OF the "meteorite, :"
the direction of motion being also indi-
Gated by arrows. OF course the reader
will understand that the size of the ell
ipse, az compared with the esrth's
orbit, and the proportion Of its longest
to its ehortest diameter, are not neoessa-
rily those indicated by the figure.
The two orbits intersect at A !;
they do not necessarily intersect
at any other point, though so
represented in the diagram. It is
evident that the meteorite may travel
around the sun in its prolonged elliptic
path, and the earth in her more nearly
circular orbit, during countless ages,
without once meeting /; just as two ships
may cross and recross the Atlantic In
opposite directions many times without
sighting " each other-much less COL
liding. But il when the earth is at the
point A, the mete orite be also very near
the common peint of intersection, there
is then danger Of a collision. Whether
they will really collide or not depends
upon the circumstances of the case. The
meteorite is travelling at the rate of (ssy)
20 miles per second, and the Garth with
a speed of 49, miles Cat this time Of the
year the earth's velocity is little great
er than that; and the earth is continual
ly pulling the stranger toward her by
the force of attraction, at q rate which
can be rigidly calculated through all the
variations In their distance. If, now,
we should project (poriions of the two
orbits on paper, mark off upon them the
place which each body would occupy at
successive instants, If there was no mu-
tual attraction, and then set off from the
meteorite path, toward the earth g places,
the distances through which the body is
drawn by the earth's at fraction, we
should have the actual path of the me-
teorite with reference to the earth; end
could see by inspection whether the two
would collide, or pass each other. In
case the meteorite is found to pass into
the earth's hemisphere, further cor
rection must be made for the retsrdation
of speed due to resistance of the air; I;
.Vd the figure would then show the
least distance between the two bodies.


There is one fact which is involved in
considering the question whether, un-
der certain geometrical circumstances,
the body would fall to the earth or rot
the character of the material Of which
it is composed. The friction OF the at
mosphere retards the motion, and that
arrested motion of the mass is convert
ed into motion Of its constituent mole
cules or atoms-it is changed into heat.
The temperature of the body is raised
to the point of incandescence, and may
be increased many thousands of de-
grees. The exterior portions are heated
more rapidly than the interior, as the
heat is generated from without and
this unequal heating causes unequal ex-
pansion Of the particles, 30 that there ia
continued tendency to break up from


the outside. The disjoined particles
fall away, and are left behind, because


the surface exposed to atmospheric re.


sistance is greater in proportion to the


quantity of motion in the mass fcT small


bodies than for large ones Of the same


material. If, now, q large meteorit,


were composed entirely of iron, the co


hesive attraction of its particles nigh


be Undoubtedly would be) great enough
10 Withstand this strain and the mas