42 GENERAL PROPERTIES OF LIVING TISSUES 



is measured in fractions of a Daniell cell, or any 

 other constant element, by bringing into the same 

 circuit with the current of injury, but in an op- 

 posite direction, so much of the current from the 

 cell as will exactly balance the current of injury, 

 i. e. so much as will keep the meniscus of the 

 electrometer from moving in either a positive 

 or negative direction when connected with the 



o 



circuit. 



Advantages of the Electrometer. The mass of 

 mercury displaced in the movement of the menis- 

 cus is very small, and the distance through which 

 it is moved is short. Hence the inertia of posi- 

 tion is easily overcome and the inertia of motion 

 (which is proportionate to the mass times the 

 square of the velocity) is practically wanting. 

 The absence of inertia errors, the almost instan- 

 taneous quickness with which the meniscus takes 

 its new position, the ease with which slight elec- 

 tromotive forces (YO~OTO v lt) ma 7 ^ e measured, 

 and simplicity of construction, are the principal 

 advantages of this admirable instrument. 



The Rheochord. If two poles of a cell or 

 other points of different potential be joined by 

 a well-drawn wire, the potential through the 

 wire will fall uniformly from the anode to the 

 cathode. The greater the resistance in the wire, 

 the more uniform will be the fall in potential. 



