THE LAYING OF SXJBMAKINE CABLES. 139 



possibly at a varying angle crossing and re-crossing the assumed 

 course as these conditions vary. The result is that more slack 

 is laid than intended, due to the cable taking an irregular 

 course from one position to another. Further, the percentage 

 slack calculated by the log is higher than that actually laid 

 along the course taken by the ship under these conditions, in 

 consequence of the fact that the log registers only when the 

 ship moves relatively to the water. 



In the control of the amount of slack paid out, it is evident 

 that there must be enough to avoid festooning, to ensure 

 the cable lying comfortably on the bottom, and to admit of 

 raising it again for repair without undue strain, while on 

 the other hand it is too costly to lay more slack than is 

 absolutely necessary to provide for the above conditions. 

 Under these circumstances it is evident that the greatest 

 accuracy attainable in determining the p8r2entage slack is 

 to be desired. Messrs. Siemens Bros, and Co. with the view 

 of avoiding such sources of error as those alluded to above, have 

 devised and adopted with success a very ingenious method 

 by which the distance actually travelled over ground is 

 measured and a continuous indication given of the percentage 

 slack paid out. The principle of the method is to pay out 

 perfectly taut and without slack a fine pianoforte steel sound- 

 ing wire at the same time as che cable. The wire thus lies 

 straight on the sea bed and the length paid out is a correct 

 measure of the distance travelled by the ship over ground. 

 Therefore the speed of paying out this wire, compared to the 

 speed of paying out cable, both measurable with accuracy on 

 board, gives the amount of slack. To avoid taking measure- 

 ments continuously of the lengths of cable and wire paid out 

 during given periods of time, and to afford a continuous indica- 

 tion of the slack, Messrs. Siemens Bros, have designed an 

 ingenious instrument to register the difference in speed of the 

 cable and wire, and indicate directly in percentages of slack. 

 The wire passes through the guides of a friction table for 

 holding it taut, round a small drum and over and under dyna- 

 mometer pulleys arranged exactly as for the cable but of much 

 lighter construction. Light spindles are fixed to the cable and 

 wire drum axles and revolve with them. On one of these is 

 mounted a long wooden cone truly revolving with the spindle 



