DIASTROPHISM AND THE FORMATIVE PROCESSES .407 
factor. The sphere of control—as against the sun at the distance 
of the earth—of a mass 1/20 of that of the earth is 458,000 miles in 
diameter. A mass no greater than 0.000,000,296 of the mass 
oi the earth has a sphere of control 8,200 miles in diameter 
(MacMillan). The functions of spheres of control in the genesis 
of planets are a feature that has been too much overlooked.* 
53. Asymmetry in a planetary core was likely to make itself 
felt in the distortion of the mass later built upon it. The inherited 
notion that the earth core, if liquid, would be merely a melt whose 
solidification would have to await the progress of freezing from its 
surface downward belongs to an old order of thought. The solidify- 
ing process should rather be studied as progressive supersaturation 
and precipitation. The formation of the solid core doubtless 
depended chiefly on the order in which the various possible minerals 
were formed and the extent to which they settled toward the center. 
The inherited and convectional motions doubtless affected the 
lodgment of the precipitates and rendered the growth of the core 
more or less asymmetrical. 
54. Such external forces as gave rise to changes in the rate of 
rotation, or produced tides or nutations, must have played their 
part in distorting the forming core. 
THE SIZE OF THE PLANETESIMALS 
55. At the outset, the planetesimals were merely the molecules 
of the scattered solar gases or the minute precipitates formed from 
these or else the molecules which escaped later from the nuclei. 
Starting thus small, and conditioned by their wide dispersion,. 
their growth was necessarily not only slow but precarious.* 
56. The Zodiacal Light is reflected by minute particles that 
probably have orbits of the planetary type, and hence are in fact 
“Table of Dynamic Properties,” ibid., p. 478. For function of spheres of 
control, see Article XI, zbid., pp. 128-34. - 
2 ““The Critical Conditions That Controlled the Passage of the Nuclei into Collect- 
ing Cores,” Article XII, ibid., pp. 477-500. 
3 “Exterior Agencies That Affected the Planetary Cores during Their Formation 
and Afterward,” ibid., pp. 500-504. 
4“The Nature of the Planetesimals at the Start,” Article XIII, zbzd., pp. 666-71. 
