from Ordinary Materials. 533 



is the capacity of the "Uranium Pot" used (a lead cylinder 

 17 cm. high and 9 cm. in diameter, with a central wire 

 electrode), the unit of potential the volt, and the unit of time 

 the minute. 



Since the reading of one electroscope did not wholly occupy 

 the attention of the observer, two exactly similar but entirely 

 separate sets of apparatus were used : thus two experiments 

 were proceeding at the same time. On several occasions the 

 same experiment was tried successively with the two electro- 

 scopes, and excellent agreement between the results obtained. 



§ 3. A few preliminary experiments were made with 

 vessels of the same dimensions as the "Uranium Pot," but of 

 the most diverse materials — metals, woods, paper, porous pots 

 saturated with electrolytes, &c. The leak in all cases was of 

 the same order of magnitude, the extremes differing in the 

 ratio of 7 to 1. 



§ 4. The first method by which information was sought as 

 to the nature of the ionizing influence was the measurement 

 of the relation between the ionization and the volume in 

 vessels of special form. 



Rectangular vessels were constructed of wood, of which 

 one side could be moved parallel to itself through a consider- 

 able range (fig. 2). The walls were covered with the material 



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under investigation, carefully cleaned with sandpaper and 

 charged to a high potential : the current through the gas to 

 an electrode of wire netting, suspended by a stiff wire passing 

 through a sulphur plug and guard-ring in the fop of the vessel, 



