404 THOMAS C. CHAMBERLIN 
Monoecious secondaries may arise as:orbital ultra-atmospheres’ do, 
and in similar ways, and are normally minute. They thus probably 
attend all stars in prodigious numbers but small mass. Dioecious 
secondaries are assigned to the dynamic action of a passing body 
on an eruptive sun by first stimulating an effective outburst and 
then drawing the projected matter into orbits about the mother- 
body, a purely dynamic function. ‘The eruptions are quite sure 
to take place by successive impulses, and a part of each belch is 
likely to remain under self-control and act as a collecting center 
for the more scattered planetesimal part. Thus the main mass 
will be gathered into a comparatively few, rather large planets. 
44. While thus monoecious systems may be nearly universal, 
dioecious systems can arise only when the necessary dynamic 
encounter takes place. Close approaches of stars are rare events; 
there is, therefore, no reason to suppose that planetary systems /zke 
our own are common in the heavens. Only one such is known. 
Still, rarely as one star closely approaches another, the multitude 
of stars and the great length of celestial time makes possible a 
fairly large number of even this very peculiar class of secondaries. 
It is a logical error to base arguments on the assumption that 
planetary systems of this type are universal or even necessarily 
frequent attendants of stars. 
4s. The cosmological rescrutiny brought out in ies: terms 
than before the extreme improbability that a planetary system 
like our own would arise from any form of centrifugal action in a 
condensing gaseous or quasi-gaseous nebula. The principles of 
the kinetic theory of gases, combined with the dynamic considera- 
tions that lie back of the Roche limit? and of the new criterion 
of Moulton, indicate that all such action would result in minute 
secondaries without effective collecting nuclei, a condition which 
practically inhibits the formation of large planets.* 
1 The Origin of the Earth (1916), ‘‘Celestial Kinships,” p. 21. 
2F. R. Moulton, ‘On the Application of Roche’s Limit and a New Criterion of 
Somewhat Similar Character,” Astrophys. Jour., Vol. XI (1900), pp. 120-26. 
3 Ibid. 
4“‘Selective Segregation of Material in the Formation of the Earth and “Tts 
Neighbors,” Article XI, Jour. Geol., Vol. XXVIII (1920), pp. 137-44. 
