NARRATIVE OF THE CRUISE. 



81 



1 foot in diameter at the centre, tapering towards the ends, and was capable of sup- 

 porting in the water a weight of 70 lbs. If necessary, two or more buoys were used. 



A boat was generally used to obtain the current observations. The first operation was 

 to find out the direction and rate of the surface current by attaching the boat to the dredge 

 rope and letting it go from the ship ; the boat thus became anchored by the dredge. The 

 surface current log was now hove and allowed to run out for from six to twelve minutes. 

 The current log ship was made of a triangular piece of wood, with a weight at its apex, and 

 it was kept close to the surface by an oar lashed across its base ; the current log-line was 

 marked to fathoms. When the log-line had been running a certain time it was checked, 

 and the bearing of the log ship taken, which gave the direction of the current ; the num- 

 ber of fathoms run out, divided by the time it was running (expressed as a fraction of an 

 hour), gave the velocity per hour. 



yttod pom-.' 



— SO fmt 



Wntchbu^f 



lOOfms Watchbuo? 



200 fins Wntc!} buoy 



Scale of 5 Cables - 1 Mile 



TWH" 



Fig. 26. — Diagram to illustrate the action of the Current Drag. 



The current drag was next lowered to a depth of 50 fathoms, and the watch buoy 

 attached. The boat now followed the buoy, keeping close to it, but taking care not to 

 touch it in any way. The surface current log was next put over the boat's side, with a 

 line attached, and the time when it was put over noted. This log was now perfectly 

 stationary with reference to the surface water, moving exactly as the surface water moved, 

 whilst the watch buoy of the drag was affected by the movement of the water at 50 

 fathoms. The boat continued to follow the watch buoy for from six to twelve minutes 

 after the surface log had been put over, paying out line to the surface log. After a given 

 interval the line to the surface log was checked, its bearings taken, and the number of 

 fathoms run out, with the time it took to run out registered; this gave both the direction 

 and rate of the movement of the watch buoy of the drag through the surface water ; but 



(naer. chall. exp. — vol. i. — 1884.) 11 



