$6 SOUTHERN CALIFORNIA ACADEMY OF SCIENCES 
section, a circle whose radius — 4034 miles, has an area of more 
than 50 million square miles. This long cylindrical space 
through which we sweep daily contains more than 144 million 
< 50 million = 75 million million cubic miles. More aceur- 
ately it is over 80 million million eubie miles. Since in this 
space we touch 20 million little masses, to each one there is a 
space of 4 million cubie miles. Each little mass, a shooting star 
when it enters our air, has around it 4 million cubic miles of 
free space. In general, it is at the center of a cube of space 
each edge of which is about 160 miles long. From center to 
center of such spaces is 160 miles. 
We thus find that throughout the space traversed by our 
earth in its journey around the Sun embryo shooting stars, 
while always in motion, are distributed at intervals of about 160 
niles. 
Origin 
Comets move in planes which all pass through the Sun, but 
eut each other at all angles. They therefore move through 
space in all conceivable directions. When nearing the Sun 
their volatile matter is driven off in streaming tails of great 
iength, and much of it, disrupted and seattered, lost to the 
parent body, pursues at intervals approximately the same gen- 
eral path as formerly. 
Not a few comets pass close by the earth’s orbit, crossing it 
at different points and at different angles. Some of these, as 
in the well known ease of Biela’s comet, have been shattered 
by disintegrating forces. They have ceased to appear as comets. 
In their stead, when due, are showers of shooting stars—the 
débris of the disrupted comets. That part of the passing débris 
swarm which enters our atmosphere is checked by the air’s re- 
sistance, aS was shown, and falls to the earth. The rest passes 
by until, on another round, it again grazes us, and is again 
diminished by another star-shower. 
This doubtless is the origin of shooting stars which come in 
showers—like the Bielids every thirteen years, and the Leonids 
at intervals of thirty three and a third years—also of stragglers 
which, hke the August Perseids, come annually. 
Possibly, in the débris of shattered and shattering comets we 
have the origin of all shooting stars. 
Effects 
We have seen that a shooting star weighing 1-84 of a pound 
