[robebtson] 



INSULATED METALLIC CONDUCTORS 



125 



To further investigate the effect of varying the amount of ionization, 

 some measurements were made on the charge acquired b;y the inner of two 

 lead cylinders when some radium in a small glass tube was placed witliin 

 the inner cylinder and successively surrounded with a series of different 

 thicknesses of sheet lead. In each case the charge acquired by the 

 Insulated cylinder rose in half a minute or less to a maximum value. 

 From Table X a comparison can be made of the values of the charge 

 acquired in each case, and of the relative intensities of the radiation 

 used to hasten the action. The intensities were compared by placing 

 the radium with its different coverings at a fixed point near the electro- 

 meter, and measuring the current from the needle to the free quadrants. 



TABLE X. 



Remarks on manner of screening 

 radium. 



In glass tube 



First covering of lead 



Second covering 



Third covering 



1st reading 



2nd reading 



Fourth covering 



1st reading 



2nd reading 



Limiting charge 



(Negative). 

 Arbitrary Scale. 



7.0 

 7.0 



6.8 



6.8 

 6.5 



6.2 

 6.7 



Intensity of radiation 

 Arbitrary Scale. 



304 

 210 



188 



167 

 167 



135 

 lâ5 



It will be seen that while there were slight changes in the value of 

 the charge acquired, these were by no means proportional to the changes 

 in the intensity of the radiation. 



One must conclude, therefore, that, although variations do occur 

 in the charge acquired by the inner cylinder in combinations such as 

 those investigated, these can not be due to changes in the amount of 

 ionization produced by the earth's penetrating rays. They may possibly 

 be due, however, to some changes in the surface of the metals themselves, 

 01 to changes in the radiations given off by these metals. 



