PEINCIPLES OF CONSTRUCTION. 



105 



■withstand the strains at high speed, and it is claimed that with 

 the special form of swivel roller bearings used under each of 

 the three discs the machine can be operated with a motor one- 

 third the size of that usually adopted with plain bearings. 



The shore-end machine shown in Fig. 44 is arranged for 

 driving by separate engine, so that the speed can be varied, 

 but electric motors are now largely used for the individual 

 drive of these machines, as all the speed regulation required can 

 be easily obtained by their use. 



New Drum 

 of Core. 



Eartli Earth 



Fig. 51. — Joint Test. 



The bottom ends of cable in each tank are connected to the 

 test room, and the various sections tested during sheathing and 

 coiling. When a new length of served core is jointed on a 

 special test of the joint is made by the well-known accumula- 

 tion test. Tbe joint is placed under water in a gutta-percha 

 trough usually suspended by gutta-percha cords in order to 

 obtain good insulation, and the test made as indicated in 

 Fig. 51. 



A metal plate is laid in the trough and connected to a key 

 which in its position of rest puts the plate in connection with 



