34 Mr. E. M. Wellisch on the Motion of 



gas was reduced. When once this separation had been 

 effected all the preceding anomalies disappeared ; the law 

 pk = const, was verified for the negative ion in air from 

 1 atmosphere down to *15 mm., indicating that the ion 

 remains unaltered in character over this range of pressures. 

 The electrons appeared to travel freely through the gas 

 without attaching themselves to molecules. No indication 

 was found of any intermediate stage in the nature of the 

 negative carrier, the separation between the ions and th« 

 electrons remaining throughout clearly marked. 



In the present experiments these results have been extended 

 to other gases : in accordance with expectation, the abnormal 

 mobility values found by previous investigators for the 

 negative ions in hydrogen and carbon dioxide were shown 

 to be capable of a similar explanation, all anomalies dis- 

 appearing as soon as the resolution of the carriers into ions 

 and electrons was effected. 



A brief study has been made of the motion of free electrons 

 through carbon dioxide at relatively high pressures; in 

 addition, the motion of ions through a number of vapours 

 has been investigated. 



A few discussions bearing upon the physical interpretation 

 of the results have been included : in particular, certain 

 outstanding problems of ionic theory have been specially 

 considered. 



2. Experimental Method and Arrangement. 



A description of the experimental method and apparatus 

 has already been published ; on this account it seems ad- 

 visable to repeat here only the essential features, reference 

 being made to the previous paper for further details. More- 

 over, advantage will be taken here to enter into greater 

 detail in connexion with certain features of the method to 

 which only a brief allusion was previously made. 



The method employed in the determination of the mobi- 

 lities was that devised by Franck and Pohl *. The ionization 

 vessel (v. fig. 2) consisted of a brass cylinder divided into 

 two compartments by a brass partition containing a circular 

 aperture. In the upper compartment was a copper plug on 

 which a layer of polonium had been deposited ; great care 

 was taken that the radiation from the polonium was con- 

 fined to the upper compartment. A circular electrode A was 

 situated about 3 cm. above the aperture and was in metallic 



* Franck and Pohl, Verh. Deutsch. Phys. Ges. ix. p. 69 (1907). 



