ORIGIN OF THE EFARTH—PAGE 167 
the early history or origin of our galaxy 
of stars and even of the whole universe. 
The solar system regularities noted by 
Kant clearly indicate that the planets 
had a common origin; ever since Kant’s 
time it has been the fond hope of cos- 
mogonists to establish the exact nature 
of that origin from further studies of the 
over-all pattern of the solarsystem. The 
first clue of this sort to be noted was 
the spacing of the planets; they are not 
at irregular distances from the sun, but 
spaced approximately in geometric pro- 
gression—that is, the distances can be 
calculated roughly from a formula called 
Bode’s law after its discoverer. Since 
the planets continue to move in the same 
orbits year after year, this spacing must 
have been established during their for- 
mation. 
A second possible clue to the origin lies 
in the progression of planet sizes—from 
the smallest, Mercury, which is nearest 
the sun, increasing through Venus, Earth, 
and Mars to Jupiter, the largest, then 
decreasing through Saturn, Uranus, and 
Neptune to Pluto, a small planet, and 
most distant from the sun. 
Further clues will be noted as we fol- 
low, now, the twentieth-century history 
of speculation on the birth of the solar 
system, from Chamberlin to Weizsicker 
and Whipple. Each of these theore- 
ticians has started either from the Kant 
nebular hypothesis, or from the Chamber- 
lin two-star hypothesis, and tried to 
show by more or less exact reasoning that 
the presently observed solar system 
would have resulted naturally. Cham- 
berlin and Moulton in 1900 guessed that 
the close approach of another star to our 
sun would raise great eruptions on the 
sun, that hot solar material would con- 
866591—50 —12 
EDGE OF THE. SUN 
o MERCURY 
O VENUS 
O EARTH 
'O MARS 
ASTEROIDS 
JUPITER 
NEPTUNE 
ae 
2 
© PLutro 
Figure 2.—Scale of planet 
sizes. 
