THE PHENOMENA OF ELECTROSTATICS. 



219 



Fig. 156. 



Figure 156 shows the bent end of a metal rod with a sharp 

 point at P. When the lines of force emanate from all parts of 

 the rod as shown in the figure, the total force acting on the rod 

 is zero, if it is at some distance from surrounding objects. When, 

 however, the lines of force near 

 the point break down, they no 

 longer pull on the rod, therefore 

 the pull due to the lines of force 

 at b is unbalanced, and the rod 

 is acted upon by a force pulling 

 it to the left. The electric whirl 

 is an arrangement of pointed rods bent as shown in Fig. 157, 

 and mounted on a pivot on an insulating stand. When this 

 arrangement is connected to an electric machine, it is set into 

 very rapid rotation by the unbalanced pull of the lines of force 



which emanate from the portions 

 b of the rods, as shown in Fig. 

 I 5 6. 



125. The mechanical theory of 

 electricity and the atomic theory 

 of electricity. The study of elec- 

 tricity and magnetism as repre- 

 sented in the foregoing chapters 

 (with the exception of seyeral mat- 

 ters which are discussed in Chap- 

 ter I) is independent of any con- 

 sideration of the nature of the physical action which leads to 

 the production of electromotive force by a voltaic cell or dynamo ; 

 it is independent of any consideration of the nature of the physical 

 action which constitutes an electric current in a wire ; it is inde- 

 pendent of any consideration of the nature of the disturbance which 

 constitutes a magnetic field ; and it is independent of any con- 

 sideration of the nature of the disturbance or stress which consti- 

 tutes an electric field. This kind of study of electricity and mag- 

 netism may very properly be called electro-mechanics. 



Fig. 157. 



