146 ELEMENTARY LESSONS ON [CHAP. in. 



size of the cell, the conducting qualities of the liquid, 

 the thickness of the liquid which the current must 

 traverse, etc. 



The exact definition of the strength of a current is 

 as follows : The strength of a current is the quantity of 

 electricity which flows past any point of the circuit in one 

 second? Suppose that during 10 seconds 25 webers of 

 electricity flow through a circuit, then the average 

 strength of that strong current during that time has 

 been 2^ webers per second. The usual strength of 

 currents used in telegraphing over main lines is only 

 from five to ten thousandths of a weber per second. 



If in / seconds a quantity of electricity O has flowed 

 through the circuit, then the strength C of the current 

 during that time is represented by the equation : 



Moreover, if C represents the strength of the current, 

 the total quantity of electricity that has passed through 

 the circuit in a given time, / is found by multiplying the 

 strength of the current by the time ; or 



Q = C/. 



For the quantity of electricity that is thus transferred 

 will be proportional to the strength of the flow, and to 

 the time that it continues. 



The laws which determine the strength of a current 

 in a circuit were first enunciated by Dr. G. S. Ohm, who 

 stated them in the following law : 



ISO. Ohm's Law. The strength of the current 

 varies directly as the electromotive -force, and inversely 



1 The terms "strong," "great," and "intense," as applied to currents, 

 mean precisely the same thing. Formerly, before Ohm's Law was properly 

 understood, electricians used to talk about "quantity currents," and 

 "intensity currents," meaning by the former term a current flowing through 

 a circuit in which there is very small resistance inside the battery or out ; 

 and by the latter expression they designated a current due to a high electro- 

 motive-force. The terms were convenient, but should be avoided as mis- 

 leading. 



