170 



LETTER TO GORDON. 



two coils m and n are of equal strength and the needle stands 

 at zero. Then the fault / lies midway, and the distance from 

 the coast can be calculated. 



cable 



vmearth 



VMX earth 



Fig. 1. 



With well -insulated wires this can be done with perfect 

 exactitude, with badly insulated ones, such as the Bona cable, 

 at any rate approximately correctly. - - Mr. Viechelniann has 

 left the apparatus in the custom-house of Marseilles at your 

 disposal. In the telegraph office there lies a letter from Viechel- 

 mann to Newall, in which the authority for its delivery is 

 contained. 



As regards the cable theory the following is my view. 



If A B (Figure 2) represents a flexible piece of cable, 

 which is attached to the sky by a weightless wire B C, the 

 cable will fall to the ground, without being able to deviate 

 from the straight line in the suspended part, as at every point 

 it falls with equal velocity, m n, op are of equal length. 



Fig. 2. 



Every point falls with equal velocity, and the new connecting 

 line n p must again be a straight one. The active force 

 pulling upon the wire B C during the fall is K = Q . sin a, 



