59 ELECTRICAL UNITS. 



Magnetic force. Magnetic field \h'~\. This is the force which 

 acts on unit of magnetic mass ; hence, 



[>'] = [/] [/-' 



Magnetic potential [<?']. The magnetic potential is the work 

 of the magnetic force that is to say, the product of this force by 

 a length; we shall have then 



Strength of magnetic shell [<]. The magnetic strength of a shell 

 is the product of the surface density by the thickness of this shell, 

 which gives 



[</,] = [L~*M*]. 



608. ELECTROMAGNETIC SYSTEM. Quantity of magnetism [Q]. 

 In the electromagnetic system, the starting-point of the measure- 

 ments is the definition of the quantity of magnetism by Coulomb's 

 law, 



= ; where [Q'] 



They are, of course, the same dimensions as those of the unit 

 of electricity in the electrostatic system. 



Surface magnetic density [.2T']. Magnetic force ; strength of the 

 field [H'J. Magnetic potential [E']. It follows from the preceding 

 remark that the dimensions of these various units will be the same 

 as those of the corresponding electrical quantities in the electrostatic 

 system ; that is to say, 



