DIASTROPHISM AND THE FORMATIVE PROCESSES 483 



overmatch the molecular escape, it should have grown to its present 

 size. It is not best just yet to try to decide what this minimum 

 may have been, but let it be placed as low as yV of the present mass 

 of the earth to make the gap between our two pictures wide. Its 

 sphere of control would then have approached 500,000 miles in 

 diameter and the mean density for the whole sphere .0011, on the 

 air standard. The spheres of control are here computed on the 

 supposition that the matter in each case is distributed in spherical 

 form and that each concentric layer is homogeneous. Actual 

 spheres of control are not strictly spherical and the distribution of 

 matter at least in the early stages was probably not homogeneous. 

 The figures given are themselves only convenient approximations, 

 but they serve well enough to indicate the general order of tenuity. 

 Only gravitative attraction is taken into account. The phenomena 

 of comets' heads imply that there is a supplementary force in such 

 very diffuse bodies, perhaps electromagnetic, but that may be 

 regarded as merely a "margin of safety" in this discussion. 



Among the points to be noted, though they cannot be discussed 

 here, are: (i) the high degree of tenuity, which gives some notion 

 of the extent to which matter may control itself in the terrestrial 

 part of the solar domain; (2) the temperature produced by the 

 expansion of the solar gases to this degree of tenuity; (3) the 

 facilities for radiation afiforded by this tenuity; (4) the nature of 

 the internal movements in such tenuous bodies. 



I. The motions inherited from the solar eruption and their co- 

 operation with convection in modifying the condensation of the nuclei. — • 

 The gaseous matter erupted from the sun inevitably carried into 

 its new activities some measure of the turbulence that previously 

 affected it, while the forces of ejection added to this their own 

 differential impulses. In so far as these impulses had uniform 

 effects on all parts of the erupted mass, they merely served to send 

 the whole out into its orbital course. This does not specially 

 concern us here, but we may note in passing that the uniform 

 increments of motion discovered by Pettit in the solar eruptions of 

 May 29 and July 15, 1919, seem to be singularly felicitous factors 

 in promoting projection into orbits without those high tendencies 



