HYPOTHESIS OF CAUSE OF GLACIAL PERIODS 561 
deserve a place among the undetermined sources of atmospheric 
material. 
It is among the possibilities that the sun itself may be a direct 
source of atmospheric feeding. The speed at which the solar 
prominences are projected from the sun has been observed to 
exceed the parabolic velocity of the sun;" that is, the rate of 
projection is such that if the outer atmosphere of the sun does 
not effectually interfere, the gases are shot away beyond even 
the sun’s control. A much less speed could carry the gases to 
the earth, so that, unless the outer atmosphere of the sun inter- 
poses effectual barriers, it is not improbable that gases are 
thrown as far out as the orbit of the earth. The earth probably 
cannot hold hydrogen, the chief gas of these prominences, 
permanently as such, but it may do so when combined with oxy- 
gen. The shooting of solar hydrogen through our atmosphere 
would lead to the formation of water, because, even at ordinary 
temperatures, such of the molecules of oxygen and hydrogen as 
collided with the requisite velocity would enter into union. 
There seem therefore grounds for placing this among the possi- 
ble but undetermined sources of supply for our atmosphere and 
hydrosphere. When the mystery of the zodiacal light and the 
gagenshein shall be solved, it is possible that demonstrative 
evidence of our relations to the extreme projections of the solar 
atmosphere may be available. 
In the present state of extreme uncertainty relative to all 
these possible sources of supply, a hypothesis which necessarily 
involves them proceeds with uncertain steps and must perforce 
wait patiently for more definite determinations, but the pressing 
of a hypothesis which lays emphasis upon them is but giving 
effect to the fundamental mission of all working hypotheses. 
VARYING RATES OF ACTION 
By the terms of the hypothesis the state of the atmosphere 
at any time is dependent upon the relative rates of loss and gain. 
tThe Story of the Sun, by SiR RoBERT BALL, pp. 185-188; The New Astronomy, 
LANGLEY, p. 61. 
