6 Trans. Acad. Sci. of St. Louis. 



d ' ~ b m AZ\R~ R )' 



where R and R 1 are the successive radii to which the mass 

 has shrunk. This may be put into the form 



5 m 



r 2 c R -> 



AnrA l -t\ (12) 



For the case of a nebula filling the orbit of Neptune and 

 then shrinking to the present dimensions of the sun, we note 

 that i? =6570i?; and hence Ave may conclude that if the 

 primitive nebula extended only to the limits of the planetary 

 system the above value of 6 in (11) would have to be dimin- 

 ished by about one six-thousandth part. Therefore we see that 

 nearly all the heat of the sun has been developed since the 

 primitive nebula attained the dimensions of the solar system. 

 The following table shows the amount of heat developed by 

 the solar nebula (assumed to be homogeneous) at different 

 stages of its contraction. 



The table shows clearly that the principal part of the sun's 

 heat was developed at a late stage of its contraction. Thus 



