16 
larger portion, four-fifths by assumption, of 
the matter of the earth would yet be in the 
meteoroidal form and doubtless more or 
less closely associated with the growing 
nucleus. If the infalling of this four-fifths 
of the material of the earth were duly 
timed, so as to be neither too fast nor too 
slow, it would give by its impact upon the 
atmosphere of the earth a sufficiency both 
of heat and of light to maintain life upon 
the surface of the earth. The plunging- 
down of these meteorites upon the surface 
might be more or less destructive to the 
life, but only proportionately more so than 
the fall of meteorites to-day. It would not 
be necessarily fatal to life, especially oceanic 
life; indeed, the strokes of the meteorites 
might not be more inimical to the per- 
petuity of any given form of life then than 
are the attacks of its numerous enemies 
to-day. It was only another form of 
jeopardy. The latitude as to variation 
of rate of infall would be rather large. 
The infall must not have been so rapid 
as to have given a universal surface 
heat above 100°C. The life of hot springs 
crowds close upon this upper limit, as Lord 
Kelvin has indicated. The infall must not 
have been so slow as to have permitted the 
surface heat to fall universally below 0° C., 
making allowance for other sources. These 
other sources might have permitted the 
meteoric supply to fall considerably below 
the quantity represented by a surface tem- 
perature of 0° C. Between this indetermi- 
nable low point and a supply equivalent to 
100° C., similarly qualified, there is a quite 
wide range. Those who have insisted upon 
the precipitate infalling of meteorites at 
such a rate as to reduce the earth to a 
nebulous condition will probably not feel 
entitled to doubt the adequacy of this 
source of light and heat. They can only 
question the possibility of the meteorites 
falling in slowly enough to permit the coin- 
cident presence of life on the earth. 
SCIENCE. 
[N. S. Vou. X. No. 236. 
This hypothesis starts life at a period 
when the earth was one-fifth grown and 
prolongs it throughout the rather slow 
gathering-in of the last four-fifths of the 
earth’s mass, and hence gives to the earth 
a long era of autogenic life conditions. 
Now, if a hypothesis relative to the early 
constitution and the growth of the rest of 
the solar system concordant with this be 
entertained, that is, a constitution of a pre- 
dominantly meteoroidal rather than a gas- 
eous condition, and of a slow rather than a 
precipitate aggregation, it will, perhaps, 
appear that the output of heat by the sun 
in the stages concurrent with this auto- 
genic life period of the earth may have been 
small. The autogenic thermal era of the 
earth may thus have corresponded to a 
period of slight thermal loss by the sun. 
As time went on the ingathering of the 
terrestrial meteorites gradually became 
more and more distant from one another 
(since the scattered material was progress- 
ively exhausted by previous infalls), while 
the central or solar aggregation was yet 
only in its early stages and was gradually 
increasing in heat. If this increase was in 
a ratio somewhat proportionate to the de- 
cline of the autogenic heat of the earth‘an 
equalizing compensation might result, and 
the earth gradually pass from the relatively 
independent autogenic thermal stage to the 
dependent solar stage which has continued 
to the present. Thus, by the prolonged 
coincidence of increase on the one side with 
decrease on the other, the life history of the 
earth may have been transferred from 
meteoroidal to solar dependence without 
such a radical disruption of continuity as 
to have been. generally destructive. 
This speculation may seem at first thought 
to be far-fetched, and to be poised on a 
ticklish combination of conditions, and it 
may, indeed, prove, when critically studied, 
to be really so, but yet it is submitted that 
it follows along coherent lines connected 
