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 iiot 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 tliis 

 virtually concedes the possibihty 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 living thing to have been produced in some way can 

 hardly escape supposing this living thing to have become ahve; but 

 neither does he escape facing a mystcrj' 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 livmg thing? There can be no more need of so doing 

 than of trj'ing to imagine a time when the mii verse began to exist. 

 Parts of the universe may always have been alive. Yet granting this 

 possibilit5^, it may be argued that since no life could have existed 

 upon the earth when it was a molten sphere we have still to accomit 

 for the presence of life upon it to-da}-. 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.^ 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 do'miward coinse 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 thej^ 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 reciuired 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 these dust particles it might be 



1 Pan-sper' mi-a < Gr. yan, universab sperma, seed or Hving germ. 



