THE INORGANIC REALM 567 
be true if the life principle were an immaterial something 
which could find expression in an organism only through 
material bodies presenting favorable properties under favor- 
able conditions; and if life be not inherent in matter we should 
expect that all attempts to find any difference between the 
matter with which life is associated and that which is lifeless, 
would fail, as they have done. 
It may be urged against the supposition of life having entered into 
lifeless compounds as a controlling force in the beginning that this 
virtually concedes the possibility of lifeless bodies becoming alive, 
and merely substitutes a wholly mysterious idea for a chemical con- 
ception of the process. It is conceded that an evolutionist who as- 
sumes a first livmg thing to have been produced in some way can 
hardly escape supposing this living thing to have become alive; but 
neither does he escape facing a mystery whether he tries to think 
about it in chemical terms or not. Scientific thinkers try to avoid 
unnecessary assumptions. Why then should -we assume that there 
ever was a first living thmg? There can be no more need of so doing 
than of trying to imagine a time when the universe began to exist. 
Parts of the universe may always have been alive. Yet granting this 
possibility, it may be argued that since no life could have existed 
upon the earth when it was a molten sphere we have still to account 
for the presence of life upon it to-day. The answer of modern as- 
tronomers to the question as to how our earth came to be inhabited 
is afforded by the theory of panspermia.t This theory supposes that 
innumerable living spores are traveling through the celestial spaces 
impelled by the radiation pressure of light. It has been found by 
experiment that minute particles allowed to fall in a vacuum are 
driven from their downward course by a beam of light; and it has 
been calculated that spherical spores 0.00016 mm. in diameter— 
such as we have good reason for believing to exist although too small 
to be seen through ordinary microscopes—would be moved readily 
by the pressure of sunlight if they should once pass out of our atmos- 
phere. Air currents would carry such bodies to a height of about 60 
miles where, if electrified by a radiating auroral discharge they 
would be carried beyond our atmosphere and beyond the effective 
pull of gravity. The light pressure could then propel them to the 
orbit of Mars in about twenty days, and beyond our solar system in 
little more than a year. Thousands of years might be required for 
them. to reach other solar systems; but meanwhile the extreme cold, 
dryness, and other conditions prevailing in space would be favorable 
to their remaining alive and resting indefinitely. Within a solar 
system particles of dust are being attracted towards the sun. If a 
traveling spore should meet one of thése dust particles it might be 
1 Pan-sper’ mi-a < Gr. pan, universal; sperma, seed or living germ. 
? >] b 
