ELECTRIC FIELD. 



159 



The iron rod in Fig. 102, if 

 free to turn, oscillates back and 

 forth through an equilibrium 

 position parallel to the field. 



An iron plate is drawn into 

 the intense magnetic field be- 

 tween two opposite magnet 

 poles as shown in Fig. 104. 



The glass rod in Fig. 103, if 

 free to turn, oscillates back and 

 forth through an equilibrium 

 position parallel to the field. 



A glass plate is drawn into 

 the intense electric field be- 

 tween two charged metal plates 

 as shown in Fig. 105. 



glass plate 



Fig 104. 



Fig. 105. 



97. Dielectric hysteresis. The most prominent kind of di- 

 electric hysteresis is a kind which is closely analogous to what is 

 technically called elastic lag in mechanics. For example, glass 

 when subjected to a mechanical stress takes on a certain amount 

 of strain (deformation) quickly, after which the strain increases 

 slowly for a time; and when the stress is removed a remnant 

 of the strain persists for a time. 



A condenser is charged. The 

 coatings of the condenser are 

 then momentarily connected 

 by a wire which discharges the 

 condenser. The wire is then 



disconnected, and the con- 



A rubber tube is stretched. 

 (This stretch corresponds to 

 the electrical strain of the di- 

 electric of a charged condenser.) 

 The end of the rubber tube 

 is then momentarily released. 



