GLOSSARY 297 



for the existence of organic beings are established. 

 As held by Arrheniiis it teaches that when conditions 

 on the earth had become favorable to life, life origi- 

 nated from the action of life-sperms, or germs, which, 

 eternal in nature and able to survive the extreme 

 cold of interstellar space, came from space, trans- 

 ported largely by means of radiation pressure. 



The view, like most other views, is related to 

 some similar ideas of antiquity. The modern hy- 

 pothesis of panspermia was advanced in 1865 by 

 H. E. Richter. It was accepted by Helmholtz, by 

 Ferdinand Cohn, and many others. 



Parthenogenesis. Reproduction without sexual 

 union. 



Pelagic Life-forms. Life-forms that inhabit the 

 surface of the ocean far from the land. 



Perihelion. The point in an orbit (as of a planet) 

 nearest to the sun. By extension, in the theory of 

 the planetary atom, the point in the orbit of an 

 orbital electron that is nearest to the nucleus. 

 Opposed to aphelion. 



Phase. Physical Chem. In a heterogeneous sys- 

 tem, a uniform solid, liquid, or gas, or a mixture, a 

 compound, or solution, that is one of the physically 

 distinct and mechanically separable portions of the 

 system. 



Photoelectric Effect. The emission of electrons 

 caused by the influence of light. Knowledge of the 

 photoelectric effect dates from Heinrich Hertz 

 (1887). According to Ernest O. Lawrence and W. J. 

 Beams, of Yale University, electrons are ejected from 

 a metal in less than three-billion ths of a second after 

 a ray of light strikes it. 



Photosynthesis. A synthetic reaction brought 

 about by the influence of light. 



Planorhis. A pond snail. 



