154 THE MEANING OF EVOLUTION 
Place suggested that in a ring like this the material 
could not be quite evenly distributed. While every 
particle in the ring kept revolving around the sun, 
those in front of the densest part were slowly held 
back by the attraction of the thicker portion, while 
those behind it in rotation had their speed hastened 
until finally all the material in the ring had collected 
at one spot and a new planet was born. La Place 
believed that these planets formed their moons in ex- 
actly the same way, and that Saturn was simply a 
planet not all of whose moons had yet been formed. 
He believed that this happy accident served to tell us 
how the universe had been created. 
Of course, so detailed a theory concerning anything 
of which we know so little has always had much 
ridicule thrown upon it, and yet no truly competing 
theory has been proposed until very recent times. 
Within a few years a Planetesimal Theory has been 
announced, and is gaining considerable prominence, 
although it is too early yet to say whether it will 
supersede La Place’s idea. In this theory, also, the 
suggestion comes from the heavenly bodies. With 
the increasing study of the nebulz, many forms of 
these interesting bodies have been discovered. A very 
common type consists of a great coherent central mass, 
with two or more arms extending from opposite sides 
in the form of a spiral. This is as if gaseous re- 
