THE LAYING OF SUBMARINE CABLES. 



177 



the cable at the cable-house and putting it to earth can be 

 done from the town office, and the cable re-connected after the 

 storm is over. Thia is carried out by an electro-magnet at the 

 cable-house, which is set in action by a current from a few 

 tray cells on closing the circuit at the town office. The lightning 

 guards now generally in use (fixed between the land-line and 

 cable at the cable-house) are designed to perform this duty 

 automatically. The most widely-used guards are those devised 

 by Mr. H. A. C. Saunders and by the late Sir Charles Bright. 

 The Saunders lightning guard is illustrated in Fig. 88. A 

 fine fuse wire, W, connected at one end to the land-line terminal 

 and at the other to the cable terminal, is stretched through the 

 centre of the brass tube B and retained taut by the spring S. 

 The tube is to earth, and is brought into closer proximity to 

 the wire by means of the plugs AA at the ends, thus making 

 a very small air-gap between line and earth. Should lightning 



■^ 



To Earth 1 



_^ 



Zinc Earth Plate 



Fig. 88. — Saunders Lightning Guard. 



strike the land-line or cable, it will, in accordance with known 

 laws, discharge to earth through the small air gap, instead of 

 by the path through instrument coils. The size of the wire is 

 such that when the discharge is of a tension dangerous for line 

 and instruments, the wire is fused and releases the spring con- 

 tact S, which falls back to the stud on the earth stop and puts 

 the cable to earth. 



The Bright lightning guard consists of two vertical rows 

 of discharge points, arranged as shown in Fig. 89. The 

 cable is connected through a flexible spiral of wire to the rod 

 R, free to move in a vertical direction in guides. A number 

 of fuse wires are stretched across horizontally in front of the 

 rod, between the two intermediate sets of points. The weight 

 of the rod is supported by the pin (seen in the illustration) 

 resting on the top fuse wire, thus making a metallic con- 

 .nection between the cable and land-line. When the line is 



