[shaw-reilley] 



EFFECTS OF AGEI\G 



173 



The Electromotive Force of Standard Batches of Normal and of Modified 

 Weston Cells during a Period of Ten Years 



(Expressed as differences in microvolts from the international mean value). 



It should be observed that the constancy of such cells is equal to 

 that of good resistance coils. Much electrical precision work depends 

 upon the comparison of accurate resistances, involving methods 

 which could be replaced by potentiometer measurements and based, 

 instead, upon the accuracy of standard cells. It should be noted that a 

 standard cell can be made more easily, more cheaply and more rapidly 

 than any resistance coil which could be expected to remain constant 

 for several years with a similar degree of accuracy. 



The records of several exchange cells of the same age have been 

 included in the table in order to emphasize the remarkable repro- 



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