r78 



SUBMAEINE GABLE LAYING AND KEPAlRING. 



troublesome. It has now been completely neutralised by the 

 connection between coil and frame, above referred to being 

 permanently made. Of course, under these circumstances, 

 the frame must be insulated from earth, and this is done by 

 mounting the entire instrument on an ebonite base. 



For shore use these galvanometers are made with suspen- 

 sions about twice as sensitive as those for ships. The sus- 

 pensions are the same, with metal conductor top and bottom 

 (known as the strained suspension) as in the sea pattern, but 

 are lighter and capable of producing unit deflection at 42 in. 



Fig. 224. — Laboratory Type of Sullivan Galvanometer. 



focus with one Leclanche cell through 300 megohms. These 

 instruments have largely supplanted the reflecting astatics at 

 shore stations on account of the less time and attention 

 necessary to keep them in order and the increasing need of 

 reliable tests from shore for localisation of faults and breaks. 



Another type of the Sullivan instrument, some 70 times as 

 sensitive as the sea pattern, is made for laboratory use. The 

 suspension is single only In this form, the current being led 

 away from the coil by a fine wire spiral. This instrument is 

 provided with spirit levels and levelling screws, as in the illus- 

 tration, Fig. 224. 



