ORIGIN OF THE EARTH—PAGE 169 
1914:a Norwegian physicist, Birkeland, calculated that electrically 
charged particles shot out of the sun would spiral out in the sun’s 
magnetic field to definite circular orbits at distances depending on 
the ratio between the electric charge and the mass of the particles. 
This promising lead was followed further in 1930 by a Dutch mete- 
orologist, Berlage, who assumed the particles were charged atoms. 
More recently, in 1942, the Swedish physicist, Alfvén, was able to 
predict by similar reasoning that rings of gas with sufficient angular 
momentum would be formed around the sun as the sun moved through 
a nebula, but both he and Berlage have avoided the embarrassing 
problem of how this gas could condense to form planets. 
Lastly in the sequence of nebular speculations, a German physicist, 
Weizsicker, has recently investigated in detail the motion of a large 
cloud of dust and gas in rotation about a massive central body like 
the sun. From this return to the ungarnished Kant hypothesis he 
was able to show that, while most of the gas would escape into outer 
space, the planets could be formed by the accretion of the dust par- 
ticles over a period of a hundred million years—a short time compared 
to the age of the earth. The spacing of the planetary orbits Weiz- 
siicker explains in this manner: The inner parts of the rotating nebula 
would be pulled around more rapidly by the sun’s gravitational 
attraction than the outer parts. Like stirring a bowl of soup near 
the center, this would set up eddies, and at the boundaries of the 
eddies the dust would coagulate most rapidly. These boundaries, 
Weizsicker calculated, would be spaced approximately in a geometric 
progression from the sun just as the planets are observed to be. 
The Weizsicker hypothesis accounts for more of the observational 
data than any of the previous speculations, but because it is so recent 
a number of its consequences have not been explored and some of 
the estimates may need revision. 
One of the interesting consequences is that the formation of planets 
should be an extremely common occurrence. Possibly in the process 
of formation of every star the conditions would be correct to form 
planets. Thus we might expect billions, if not hundreds of billions 
of planets in our galaxy, the strong likelihood that life has developed 
on a million or more of these, the high probability that there are other 
civilizations of mankind, and even the possibility that men on other 
planets are writing articles on the origins of their solar systems! 
THE ORIGIN OF STARS 
But where did the original gas and dust come from? How was it 
started in rotation? One reason the Weizsiicker hypothesis has 
received so much attention is that a separate line of research on the 
origin of the stars has provided answers to these questions. The 
argument hinges on the energy necessary to keep the stars shining. 
