Chap, ii.] DENSITY, TENSION, AND INTENSITY. 25 



Density, tension, and intensity of an 



electric current. The intensity of a current is the 

 quantity of electricity flowing through the circuit in 

 a given time (i.e. the strength of the current), and 

 this will depend upon the electromotive force. When 

 the circuit of an element is closed, the electricity will 

 flow through the conductors or electrodes with greater 

 speed the greater the electromotive force. In a gal- 

 vanic element, quantity or intensity is conditioned by 

 the extent of surface of the plates of the cell ; the 

 larger the plates the greater the quantity. Density 

 is dependent on the quantity of electricity that flows 

 through a cross-section of a conductor in a given time. 

 Suppose the thickness of a wire to be reduced to one- 

 half, the quantity (that is, the intensity) of the cur- 

 rent flowing through it will not be altered, but the 

 current will be twice as dense flowing through the 

 thin conductor as it was when flowing through the 

 thick one. Thus the density is inversely proportional 

 to the cross-section of the conductor ; i.e. the less the 

 cross-section the greater the density. Tension is 

 defined as an outward force on the surrounding 

 medium, and measures the tendency of the opposite 

 electricities of two dissimilarly charged conductors to 

 discharge across the space intervening between them. 

 If the positive and negative poles of an element are 

 separated from one another by a space, the greater 

 the tension of the electricity the greater will be the 

 ease with which it will pass across the space. The 

 greater the difference of potentials between the con- 

 ductors, the greater will be the charges, and there- 

 fore the greater the tension or tendency to discharge. 

 Great difference of potentials can easily be obtained by 

 means of a frictional machine. Hence, sparks can be 

 obtained between the terminals of such a machine, 

 though they are separated by a distance of several 

 inches. 



