December 14, 1917] 



SCIENCE 



593 



oxide of uranium as exciting agents. Air, 

 carbon dioxide and oxygen were used as 

 sources of ions. Decay curves were also ob- 

 tained, using the arrangement shown in Fig. 2. 

 Air, oxygen or carbon dioxide under pres- 



.22 div. per min. with no ionizing agent pres- 

 ent. With velocities of 2 cu. ft. per min. 

 through the tube the leak of the electroscope 

 due to ions escaping through (E) was less 

 than .04 div. per min. 



sure was passed into a large metal cylinder 

 (H) approximately 2 meters long, thence 

 through two "Wolff bottles (F) and (E) con- 

 taining sulphuric acid and cotton wool, re- 

 spectively, into the tube (B). The acid was 

 used as a drying agent and the cotton wool 



In some preliminary work it was found 

 that, at a given velocity, ions passed through 

 the tube in a shorter time than the time cal- 

 culated from the rates of flow would indicate. 



r/M£ /N S£CS. 

 Fig. 4. 



to remove the ions produced by bubbling. 

 This experimental arrangement permitted 

 large velocities through tube (B). 



The natural leak of the electroscopes used 

 throughout this work varied between .18 and 



Spark gaps were sealed into the tube at differ- 

 ent distances from the electroscope and times 

 elapsing between the starting of the spark and 

 the beginning of the motion of the gold leaf 

 were measured by a stop watch. For short 



