
the Measurement of very small Alternating Currents. 599 
logarithms of the currents, we have a straight line delineated, 
making an angle with the horizontal, the tangent of which 
is equal to 2. If, then, we replace the ground-glass 
screen in its original position and pass through the ammeter 
Fig. 3. 
‘02 
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wire any current, continuous or alternating, lying within 
the range of the graduation, the resulting deflexion of the 
line of light on the screen can be at once marked off on the 
ground glass, and from the curve of calibration obtained 
as above described the ampere value of this current becomes 
at once known. 
In the instrument actually used the deflexion of the line 
