Cooke. — On Telegraph Cables. 335 



enclosed in a thick iron case. The desired end is thus 

 attained, but with the effect of still further reducing the 

 sensibility of the instrument. 



The other instruments in our testing-room consisted of 

 coils of fine wire of known resistances, enclosed in suitable 

 cases, on which the resistance of the coils was marked. 

 These resistance - coils were of an alloy of platinum and 

 silver, being a substance whose electrical resistance does not 

 vary so much as that of many metals with a difference of 

 temperature. German is another alloy used for resistance- 

 coils for the same reason. The resistance of the coils 

 being known, and practically unaltered from day to day, 

 the insulation resistance of the cables can at any time be 

 compared with them ; if this insulation resistance fall below 

 a certain standard it is assumed there is a defective place in 

 some part of the cable. The defect is accordingly searched 

 for, and the faulty length cut out. 



A voyage of some hundreds of miles from the Cayenne 

 ■coast brought us to the Island of Trinidad, in the West 

 Indies. Our next length of cable was to be laid from here 

 five hundred miles northward to the Danish Island of Santa 

 Cruz. On this occasion the whole length of the cable was 

 laid from our ship, so that I had an opportunity of seeing 

 the shore end landed. The place selected for the starting- 

 point was a small cove on the northern shore of the island. 

 At the head of this cove is a strip of sandy beach only some 

 20 yards long ; everywhere else the sea washes up to the 

 base of the steep forest-covered cliffs. A small structure of 

 galvanised iron stood on the beach. This was to contain the 

 electrical apparatus for testing the cable while being laid. 

 Behind this hut a path led up the hills, by the side of which 

 could be seen the poles and wires of the land telegraph-line 

 that crosses the high lands of northern Trinidad, and was to 

 link our line with the town of Port of Spain, the capital of 

 the island. It was late in the afternoon when our great 

 vessel reached the mouth of the cove. We immediately set 

 to work. The ship's boats were got out, and a raft was 

 made by fastening boards across two of the boats. The heavy 

 shore-end cable was coiled out of one of the tanks on to this 

 raft, leaving, however, one end on the ship joined to the main 

 cable ; the raft was towed to the shore, paying out cable as 

 it went ; the end of the cable was hauled on to the beach, 

 a spare piece was cut off, leaving the proper length to be 

 taken into the hut. 



A fuller account of this place and the laying of this sec- 

 tion of the cable was written by one of our electricians for 

 the Leisure Hour in 1877, the article bearing the title of 

 .-" Cable-laying in the Tropics." We were accompanied on 



