f 



[PATTERSON] SELF RECORDING ELECTROMETER 23 



The probable error in the readmgs of the instrument will depend chiefly 

 on the accuracy with which the dots on the charts can be read. This error 

 would not be more than • 5 mm. at the most, and would generally be less. 





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o 



2 



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IL 



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Cb 



CO 



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Q« 



The capacity of the needle and of either pair of quadrants is about 

 100 cm. 



In measuring the potential of the air a polonium collector was 

 used. The collector was 8' 6" above the ground and 9' from the build- 

 ing, which was 10' high to the eaves; one pair of quadrants was attached 

 to the positive terminal of a battery of 12 volts, and the other pair to 



