Cooke. — On Telegraph Cables. 333 



broken. This machinery is also used for lifting the cable 

 when a fault occurs or repairs are necessary. In laying the 

 cable passes up to the top of the tank, then above the deck, 

 round the drum of the paying-out machine, and over a wheel 

 at the stern. A dial attached to the machine shows the 

 amount of strain on the cable. 



We went on paying out cable day and night till we again 

 reached the buoyed end of the cable near Cayenne. This 

 cable-end was brought on board the ship ; the last message 

 was sent to the shore station, Demerara ; the end of the cable 

 was hauled up from the testing-room on to the deck and 

 joined to the one just hauled up from the buoy, and our work 

 in that part was completed. 



Before treating on some points in connection with laying 

 the next section it may be in place here to say something 

 about the testing-room. On the " Hooper " this was placed 

 in one of the triangular spaces left between two of the cylin- 

 drical cable-tanks and the side of the vessel. It was imme- 

 diately below the main deck. In fitting up the necessary 

 apparatus on board ship two things that do not trouble the 

 land experimenter have to be taken into account — the rolling 

 of the vessel, which would disturb the liquids of the battery, 

 and the mass of iron of which the ship is made, which is acted 

 on by the earth's magnetism in a different manner every time 

 the ship changes its course. This affects the needles of the 

 galvanometers. The invention of apparatus specially designed 

 to overcome the difficulties here indicated is due to Sir William 

 Thomson. Our batteries were of the form devised by that 

 gentleman for testing the first Atlantic cable. With several 

 modifications it is essentially a Daniell's battery — that is, the 

 metals used are zinc and copper, the latter metal being im- 

 mersed in a solution of sulphate of copper. For telegraphic 

 purposes this battery is now made without any porous cell, the 

 copper plate with the solution of sulphate of copper being at 

 the bottom of the cell, and the zinc in a solution of sulphate of 

 zinc at the top. As the former solution is the heavier it re- 

 mains at the bottom, and the two do not mix. A ^further 

 modification for use on board ship is to have the cell packed 

 with sawdust, so that the metals, instead of being in liquids, 

 are in a sort of paste, but still in the proper solutions. The 

 top of each cell was covered with solid paraffin, which kept 

 everything tight in its place, and prevented evaporation. 



The use of sawdust is very effectual in preventing the solu- 

 tions mixing, however much the ship may pitch and roll. It 

 is stated in treatises that sawdust increases the internal 

 resistance of the battery. This is of little importance in 

 testing cables, but the resistance is much lessened by keeping 

 the sawdust well moistened. We found some cells in which. 



