144 THB ELECTRICAL PHENOMENA Of MUSCLE. [OH. xn. 



In order to measure the strength (electromotive force) of such currents, 

 the mere amount of swing of the needle is only a very rough indication, 

 and in accurate work the arrangement shown in fig. 165 must be used. 



Fig. 166. Lippmann's Capillary Electrometer. (After Waller.) 



1 . Pressure apparatus and microscope on stand of which the capillary tube is 



fixed. 



2. Capillary tube, fixed'in outer tube containing 10 per cent, sulphuric acid 



the platinum wires are also shown. 



3. Capillary and column of mercury as seen in the field of the microscope. 



Pig. 167. Frog's heart. Diphasic variation. Simultaneous photograph of a single beat 

 (upper black line), and the accompanying electrical change indicated by the level of 

 the black area, which shows the varying level of mercury in a capillary electrometer. 

 (Waller.) 



