xlvi 



INTRODUCTION. 



as the force on a unit magnetic pole in a narrow cavity in the material, the cavity 

 being in one case perpendicular, in the other parallel, to the direction of the 

 magnetization: this definition however applies only in the ordinary electro- 

 magnetic units. There are a number of reasons for considering induction and 

 magnetizing force as two physically distinct quantities, just as electromotive 

 force and current .are physically different." 



In the United States "gauss" has been used much more for the c.g.s. unit of 

 induction than for the unit of magnetizing force. The longer name of "max- 

 well per cm^" is also sometimes used for this unit when it is desired to distin- 

 guish clearly between the two quantities. The c.g.s. unit of magnetizing force 

 is usually called the "gilbert per cm." 



A unit frequently used is the ampere-turn. It is a convenient unit since it 

 eUminates 47r in certain calculations. It is derived from the "ampere turn per 

 cm." The following table shows the relations between a system built on the 

 ampere- turn and the ordinary magnetic units. '• 



Table II. 

 THE ORDINARY AND THE AMPERE-TURN MAGNETIC UNITS- 



^ Bellinger, International System of Electric and Magnetic Units, Bull. Bureau of Standards, 

 13. p. 599, 1916. 





