210 MR. J. H. JEANS ON CONFIGURATIONS OF ROTATING COMPRESSIBLE MASSES. 
Tims the effective molecular weight, regarded as being determined by equation 
(184), may fall to very small values as we pass to the interior of a star. In § 43 we 
considered the tendency for greater molecular weights to occur in the interior of the 
star, and found that it would delay the stage at which the pseudo-spheroidal form 
would become unstable. It now appears that, in order to represent actual conditions, 
we should have examined the reverse tendency. Effectively lighter molecular 
weights may be expected to occur in the interior of a star, and this will cause the 
process of fission to begin at lower densities. In a general way we may expect that 
stars of greatest mass will begin the processes of fission in the earliest stages of their 
careers. If so, such a star as W Crucis, assuming that its two components have 
been formed out of the fission of a single body, must be a star of very great mass 
indeed. 
58. To sum up, we have found that a star of small mass (say xoth that of our sun), 
in which there is no great amount of atomic disintegration, and in which pressure of 
radiation does not play a prominent part dynamically, will not begin to break up into 
a binary star until it reaches a density of from one-quarter to one-naif that of water. 
In more massive stars there will be considerable atomic disintegration, and pressure 
of radiation will be dynamically important. Such stars will break up at lower 
densities than smaller stars. 
PRESENTED 
