STANDARDIZATION OF FOG CHAMBER. 



55 



where C is the total capacity and U the appropriate velocity of the ions 

 in the field of i volt per centimeter, each ion carrying the charge e, in 

 electrostatic units, positive or negative, depending on the charge on 

 the plate. 



While the apparatus as a whole apparently functioned very well, it 

 was found that the removal of the plate made no difference whatever. 

 Thus if D is the distance of the radium from the fog chamber: 



*With two lead plates each i mm. thick covering the radium, V/V-= .00298. 

 fWith two lead plates each i mm. thick covering the radium, V/V= .00800. 



The results (due to incidental reasons) are thus even larger in the absence 

 of the plate P than when it is present, although the conduction-leaks 

 are throughout negligible. It is therefore impossible to interpret the 

 results obtained or to compute the e from them. When D was 15 cm., 

 or larger, the effect of one or more thin lead plates over the radium was 

 no apparent deduction. In the adjustment given, therefore, the whole 

 region of the radium conducts and the fog chamber is merely effective 

 as a part of the region. 



44. Cylinder. If the sealed radium tubelets rr are inserted by aid of 

 a wider aluminum tube AR (closed at one end) into the axis of the cylin- 

 drical fog chamber FF, the closed end A projecting within as in fig. 18, 

 the difficulties referred to are in a measure obviated. Nevertheless, in 

 the present experiment it was thought preferable to use the fog chamber 

 for measuring the number of ions only, while an independent condenser 

 was installed for electrical measurements. 



The cylindrical electrical condenser is employed as follows: A closed 

 aluminum tube 0.62 cm. in diameter, 18 cm. long, containing weak 

 radium in sealed tubelets equally distributed along its inside, is made 

 the core of the condenser, the outer surface being 2.1 cm. in diameter 

 and leaded to an inch or more in thickness beyond. The aluminum core 

 in question is suspended axially from a fine wire leading to a sensitive 



