80 Scientific Intelligence. 



lar chemical theories. The argument is in favor of the greater 

 value of Avogadro's contribution to science, while the admirers 

 and followers of Dalton are criticized for giving him undue 

 credit. All who are interested in the history of chemistry will 

 find the book instructive, even though they fail to agree entirely 

 with its conclusions ; for it is ably written and displays much 

 knowledge of the literature of the subject. h. l. w. 



6. Electric Discharge hi Gases. — Faraday supposed that an 

 electric discharge occurs as soon as a determined discharge poten- 

 tial is reached which is sufficient to break down the dielectric. 

 This theory takes no account of polar differences. 



O. Lehman has sought to reconcile Faraday's theory with the 

 facts by the assumption of a dark convective streaming which 

 occurs before the discharge ; and which on account of the dif- 

 ferent discharge, fitness of positive and negative air, leads to the 

 formation of a positive air envelope at the cathode. J. J. Thom- 

 son, in an electrolytic theory, supposes that before the occurrence 

 of the discharge a convective dark current is formed. 



H. Sieveking, following the example of O. Lehman, has 

 employed vessels of large size in studying the question of the 

 existence of such dark currents. Lehman showed that the 

 cathode space is much influenced by the nearness of the walls of 

 the exhausted vessel to the cathode ; he accordingly used ex- 

 hausted vessels of 60 liters capacity. 



Sieveking sums up his conclusions as follows : 



(1) An investigation with a vessel enclosing an electroscope 

 suitably charged showed that a dark current did not exist before 

 the discharge. This is against the electrolytic hypothesis. 

 Furthermore the insulation of the exhausted space below the 

 point of discharge was perfect. A dissipation of electricity 

 which must accompany a dark current could not be shown by an 

 electrometer. 



(2) In wide exhausted vessels the dark space is not influenced 

 by a strong ionizing substance. This fact militates against the 

 supposition of the electrolytic theory that this region is a poverty 

 stricken one. 



(3) The experiments indicate that the double layer which O. 

 Lehman supposed to exist before the occurrence of the discharge 

 does not exist. 



(4) The very weak current which J. Elster and H. Geitel have 

 shown to exist in air, and upon which Kaufmann founded the 

 characteristics of the dark current, are not present in a space pro- 

 tected from ionization. The entire investigation leads one to 

 believe in a pure disruptive discharge. 



(5) The remarkable effect of the magnetic field on the electric 

 discharge leads one to conclude with O. Lehman, from the stand- 

 point of the electron theoiy, that powerful inner movements occur 

 in the molecules which, through rotary movements, greatly 

 influence the effect of the electric field. — Ann. der Physik, No. 7, 

 pp. 209-226, 1906. J. T. 



