THE INORGANIC REALM 567 



be true if the life principle were an immaterial something 

 M'hich 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 conipoimds as a controlling force in the beginning that this 

 virtually concedes the possibility of lifeless bodies becoming alive, 

 and merely substitutes a wholl.y mysterious idea for a chemical con- 

 ception of the process. It is conceded that an evolutionist who as- 

 sumes a fii"st living thing to ha\'e been produced m 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 thing? There can be no more need of so doing 

 than of trying to imagine a time when the uni-\-erse began to exist. 

 Parts of the miiA'erse ma}^ always have been alive. Yet granting this 

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

 iil)on the earth when it was a molten sphere we ha^'e 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 mhabited 

 is afforded by the theory of panspermia.^ This theory supposes that 

 innumerable living spores are traveling through the celestial spaces 

 impelled bj- 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. ui 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 atmosi)here and bej'ond the effective 

 pull of gravity. The light pressure could then propel them to the 

 orbit of ]\Iars 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 

 sj'stem 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. pan, universal; spenna, seed or living germ. 



