496 



SUBMARINE CABLE LAYING AND REPAIRING. 



pressing in an upward dlrecoion, so that as the levers move on 

 to the surface of the springs good contact is made. The ends 

 of the levers are tipped with gold, and the springs are of 

 platinum, these metals having been found to wear best and 

 keep a perfectly clean surface. The high insulation obtained 

 by the pillara, the accessibility of all the parts, the good con- 

 tacts made by the levers, and the adaptability of the key for 

 different tests are its chief advantages. It has the advantage 

 over the ordinary reversing testing key that the line can be in- 

 sulated if required. It is also suitable where it is important to 

 keep to one direction only of current to line. For reversals a 



Fig. 275. — Eymer- Jones Testing Key. 



modified form is used in which the centre bar is adj ustable and 

 can be moved into a position where it comes in contact 

 with either one or other of the levers in the mid-position. 

 This key is in use in the General Post Office, and is fully 

 described by Mr. Kempe in his standard work " Handbook of 

 Electrical Testing." 



The Silvertown Company use a pair of these keys mounted 

 on one board in testing rooms for insulation and capacity tests, 

 the connections being as in Fig. 276. For capacity tests key A 

 is put with both handles to the right (contact blades going to 

 left), thus putting the galvanometer to earth. The B key is 

 used for charge and discharge — that is, both handles to right to 



