[mclennan-keys] 



MOBILITIES OF IONS IN AIR 



129 



was joined to earth and the other terminal was joined by a wire, which 

 passed through an insulating plug of ebonite in the walls of the steel 

 cylinder, to the plate AB. An insulated wire PR also passed out 





through the walls of the steel cylinder and was joined up to a pair 

 of quadrants of a Dolazalek electrometer. With this arrangement 

 any desired uniform electric field, positive or negative, could be estab- 

 lished and maintained between the polonium-coated copper plate CD 

 and the electrode EH. As the range of the alpha rays from polonium 

 is only about 3-8 cm. in air at atmospheric pressure, it will be seen 

 that at a pressure of about 70 atmospheres and higher the ionized 



