58 ILLINOIS ACADEMY OF SCIENCE 
Kapteyn has suggested, the number of recent dispersive en- 
counters may have been exceptionally large and the present 
number of spiral nebulz abnormally great. 
In thus following out in some detail our conception of the 
origin of spiral nebule, we have wandered far afield from 
the planetary problem with which we started; let us return 
to the modest nebula that was drawn out, by hypothesis, from 
our sun and was destined to form the family of planets on 
one of which we dwell, As already implied, the material was 
sun-substance at the start, and of course in a gaseous state 
for the greater part, if not altogether. This gaseous matter 
was shot out in successive pulses by recurrent explosive ac- 
tion, and these pulses took the form of irregular knots attended 
by much highly scattered matter. 
Pulsatory action in a persistently explosive body like the 
sun seems to be a normal habit and is well illustrated by the 
Sun’s present action in projecting “prominences.” Such action 
is likely to become rhythmical if there are appropriate agencies. 
Such agencies may be assigned in the formation of the solar 
nebula. Every spheroid has a period of pulsation that is nor- 
mal to it, and this period is quite certain to influence the pe- 
riodicity of any impulsive agency that widely affects the body. 
Nagoaka holds that the successive explosions of Krakatoa dur- 
ing its catastrophic action in 1883, substantially coincided with 
the pulsation-period normal to the earth. The pulsation-per- 
iod of the ancestral sun may be assumed to have influenced the 
succession of explosions made imminent by the increasing in- 
fluence of the passing star. 
There was perhaps a more influential factor. It is assumed 
that the plane of the orbit of the passing star crossed the 
plane of the ancestral sun’s equator obliquely, for this seems 
to be implied by the present obliquity of the sun’s equator 
to the invariable plane of planetary system, and also by the 
anomalously low rotation of the sun which probably implies 
a reversal of the sun’s ancestral rotation. When the tidal cones 
developed by the star crossed the equatorial belt of the sun, 
they came into coincidence with its explosive belt and the 
effect was intensified by this coincidence. It was also affected 
by the superior centrifugal components of rotation that affected 
this belt. The concurrent explosive action that arose at this 
