INTRODUCTION. 179 



the first member being the energy of impact corresponding to parabolic 

 velocities, the second being identical with (P^. The former would corre- 

 spond to formation from a system of small particles each of density pi, but 

 infinitely dispersed, so that the potential energy available is (?>. It should 

 be noted also that the part E is not affected by the existence of velocities 

 in the primitive planetesimals due to attractions other than that of the 

 nucleus on which they fall, and can therefore be treated independently 

 of any supposition as to their distribution and motions previous to the 

 aggregation. 



12 



