Eight-Year Cycle in Relation to Physical Cause 119 



I'electricite a . . . fait fairc dc grands progres k 

 nos connaissances sur Ic Soleil ot celles-ci paraissent 

 aujourd'hui, commc la Physique ontiere, dominees par 

 cette nouvelle maniere d'cnvisager les phenomenes." ^ 

 In the next section we shall give attention to some 

 of these more recent astronomic theories in as far as 

 they throw light upon changes in terrestrial meteo- 

 rology which may be attributed to Venus. We shall, 

 however, carry much more to the discussion if we bear 

 in mind : 



(1) that nearly all forms of the rays we have con- 



sidered are electrically charged and are de- 

 flectible by electric and magnetic fields; 



(2) that all of the rays produce ionization of gases; 



(3) that the gaseous ions may become nuclei for the 



condensation of water vapor. 



Nearly half a century ago experiments by CouUer 

 in France (1875) and by Aitken in Great Britain 

 (1880-1881) revealed the importance of dust particles 

 in the formation of clouds and the precipitaion of water 

 vapor as rain. In their experiments upon air saturated 

 with water vapor, clouds were formed, or not formed, 

 under the same degree of saturation, according as 

 dust was present or absent. The dust particles sup- 

 plied the necessary nuclei for the condensation of the 

 vapor. 



The recent theory of ionization by radiation has 

 added greatly to our knowledge of the process of cloud 



1 Bosler: "Sur les relations des orages magnetiques et des phenomenes 

 solaires." Annales de I'Observatoire d' Astronomie Physique de Paris, 

 Tome V, 1912, p. 7. 



