4 BELL SYSTEM TECHNICAL JOURNAL 



reality the magnetization at any one point is very intense. When a 

 magnetic field is applied by bringing near the metal a permanent 

 magnet or a coil of wire carrying a current, the magnetization of the 

 material as a whole is increased to a definite value. We believe that 

 what then takes place is simply a change in the direction of the mag- 

 netizations of the domains. If we represent the magnetization of any 

 domain by a vector, the effect of the externally applied field will be 

 represented by the rotation of these vectors — rotations not accom- 

 panied by any changes of length. 



I " 



7^ 



DIRECTIONS 



OF EASY 



MAGNETIZATION 



IRON 



Fig. 2 — The positions of the atoms and the directions of easy magnetization 

 in crystals of iron and of nickel. 



Recently much has been learned about the magnetic properties of 

 materials by a study of single crystals. Ordinary metals are composed 

 of a great many crystals often too small to be seen easily by the naked 

 eye. But in the last few years methods have been found for making 

 large crystals of almost all the common metals, crystals as large as the 

 more familiar ones of rock candy and even of quartz. Experiments on 

 such crystals of iron show that they are much more easily magnetized 

 in some directions than in others. 



This dependence of ease of magnetization on direction is illustrated 

 in Fig. 2 for iron and nickel in relation to the positions of the atoms in 



