2oS The American Geologist. -^J"""' ^^^^ 
.sufficiency of energy for the sun's maintenance through such a 
prolonged history. * * * This objection is based on the as- 
sumption that the sun's heat and light are derived almost wholly 
from self-compression, as urged by Helmholtz. This self-com- 
pression has usually been computed on the basis of certain limit- 
ing assumptions, the validity of which is open to question. * * * 
The extraordinary energies displayed by radio-active substances 
are doubtless but an initial demonstration of immeasurable ener- 
gies resident in other forms of matter and in the constitution of 
the sidereal system and competent for its maintenance for unas- 
signable periods. * * * 
* * * No appeal is here made to collisions as a source of 
the parent nebula of the solar system, but only to an approach 
of the ancestral sun to another large body, and this approach is 
not assumed to have been very close. * * * 
Our present sun shoots out protuberances to heights of many 
thousands of miles, at velocities ranging up to 300 miles per 
second and more. If it were not for the retarding influence of the 
immense solar atmosphere, some of these outshoots would doubt- 
less project portions of themselves to the outer limits of the 
present system, and perhaps in some cases quite beyond it, for 
the observed velocities sometimes closely approach the controlling 
limit of the sun's gravity, if they do not actually reach it. * * * 
If with these potent forces thus nearly balanced the sun closely 
approaches another sun or body of like magnitude — suppose one 
several times the mass of the sun, since it is regarded as a small 
stai' — the gravity which restrains this enormous elastic power 
"will be relieved along the line of mutual attraction, on the prin- 
ciple made familiar in the tides. At the same time the pressure 
transverse to this line of relief is increased. Such localized re- 
lief and intensification of pressure must, it is believed, result in 
protuberances of exceptional mass and high velocity. According 
to the well-known tidal principle, these exceptional protuberances 
would rise from opposite sides, and herein lies the assigned ex- 
planation of the prevalence of two diametrically opposite arms 
in the spiral nebulae. 
Nothing remotely approaching a general dispersion of the 
ancestral sun seems to be required. The present planets and 
their satellites altogether amount to about one seven-hundredth 
part of the mass of the system Simply to supply the required 
planetary matter, the protuberances need include but this small 
fraction of the ancestral sun. However, some considerable part 
of the projected matter must probably have been gathered back 
into the sun, and some part may possibly have been projected 
beyond the control of the system. Making allowances for both 
these factors, the proportion of the sun's mass necessarily in- 
volved in the protuberances is still very small. Apparently 1 or 
2 per cent of the stm's mass would amply suffice. * * * 
