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ADVANCED ELECTRICITY AND MAGNETISM. 



lem : It is required to produce a uniform electric field parallel to the 

 ^-axisin the region of the coarse lines of force in Fig. 128, and a 

 cylindrically radiating electric field in the region of the fine lines of 

 force in Fig. 128; and to provide for the proper bounding of 



d 



d disk 



cylinder 



Fig. 128. 



these two regions. By cylindrically radiating field is here meant 

 a field like that which would radiate from a line charge lying 

 along the y-axis in Fig. 128. 



Let us assume that the metal cylinder of radius r and the 

 metal disks dd are at zero potential, and let us consider the 

 potential at any point p of which the coordinates are x and y. 

 The potential at p due to the radiating field, on the assumption 

 that the radial field reaches to p, would be: 



k log, x - k log e r 



where k is a constant; and the potential at p due to the uniform 



field would be: 



e(l - y) 



