IDEA OF POTENTIAL 



I8 7 







Fig. 126. 



each strip to be brought by proper means to a potential equal to 



the potential at the strip due to the line charge in Fig. 125. 



We would thus have the potential fixed c 



or determined at every point on the 



surface of the dotted cylinder, and the 



electric field distribution inside of the 



cylinder would be as shown in Fig. 126. 



That is, the electric field inside of the 



cylinder cc would be exactly like the 



field due to the line charge in Fig. 125, 



and this would be the case whatever the state of affairs outside 



of the cylinder cc might be. 



Example 2. A flat metal sheet A A, Fig. 127, is at zero poten- 

 tial, and a series of insulated metal strips BB very close together 



and perpendicular to the plane of the paper are brought by proper 



means to potential values such 

 that the potential V p of any 

 strip is proportional to its dis- 

 tance xfrom A A. Under these 

 conditions the region between 

 A A and BB will be a uni- 

 form electric field as indicated 

 by the lines of force in Fig. 

 127. 



Fortescue's method for de- 

 signing insulating structures. 

 The method illustrated in 

 Figs. 125 to 127 for producing 

 any assigned electric field dis- 

 tribution in a given region has 

 been proposed by Mr. Charles 

 L. Fortescue as a basis for the 

 Fig . 12 7. design of insulating structures. 



The essential features of Mr. 

 Fortescue's method may be brought out by the following prob- 



/B 

 i 



~**\ 

 IMS 



-i 



x-axis 



