an Electric Micrometer. 



557 



The curves on fig. 4 are taken from VI A., VII a., VIII A. 



In these curves the points are not very uniformly dis- 

 tributed along the lines drawn ; but this is natural, for the 

 readings were taken for such small distances (3 x 10~ 7 centim. 

 or so) that the apparatus in its present form was near the 

 limit of its working power. 



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Extrapolation was used to arrive at the results ; but it 

 was not very hazardous extrapolation, since the curve is 

 merely continued to the origin, through which it obviously 

 passes. The values obtained from the curves agree very 

 closely, the average being 037 /x^ for the smallest audible 

 impulse. 



If this is taken as a true value, the amplitude for the con- 

 tinuous uniform vibration audible cannot be greater than 



