THE ORIGIN OF LIFE 183 



heat thus generated, not to speak of the terrific impacts which 

 terminates the voyage of a meteorite. 



Arrhenius suggests a method by which microorganisms 

 might be conveyed through intersidereal space with far greater 

 dispatch and without any mineral vehicle such as a meteorite. 

 He notes that particles of cosmic dust leave the sun as a coro- 

 nal atmosphere and are propelled through intervening space 

 by the pressure of radiation until they reach the higher at- 

 mosphere of the earth (viz. at a height of 100 kilometers from 

 the surface of the latter) , where they become the electrically 

 charged dust particles of polar auroras {v.g. the aurora 

 borealis). The motor force, in this case, is the same as that 

 which moves the vanes of a Crookes' radiometer. Lebedeff has 

 verified Clerk-Maxwell's conceptions of this force and has 

 demonstrated its reality by experiments. It is calculated that 

 in the immediate vicinity of a luminous surface like that of 

 the sun the pressure exerted by radiation upon an exposed 

 surface would be nearly two milligrams per square centimeter. 

 On a nontransparent particle having a diameter of 1.5 microns, 

 the pressure of radiation would just counterbalance the force 

 of universal gravitation, while on particles whose diameter was 

 0.16 of a micron, the pressure of radiation would be ten times 

 as great as the pull of gravitation. Now bacterial spores hav- 

 ing a diameter of 0.3 to 0.2 of a micron are known to bac- 

 teriologists, and the ultramicroscope reveals the presence of 

 germs not more than 0.1 of a micron in size.^ Hence it is con- 



* Recently, by means of photography with short-length light waves, 

 the bacteria of "Foot-and-mouth disease," invisible to the highest 

 power microscope, have been revealed as rods about 100 submicrons 

 (i.e. 0.1 micron, or 0.0001 millimeter) in length, (c/. Science, May 30, 

 1924, Supplement X.) 



Germs of this dimension could be as easily transported by radiation 

 as the alleged electrically charged Stardust in the aurora borealis. It 

 may be of interest, however, to note, in this connection, that the most 

 recent theory of the aurora borealis discards Stardust in favor of 

 nitrogen snow. Lars Vegard, a Norwegian professor, ascribes the 

 peculiar greenish tint in the Northern Lights to the action of solar 

 radiations on nitrogen snow, which he assumes to exist at an altitude 



