CHAP. XX.] 



SWEEPING BY BOATS 



441 



Fig. 98. 



Fig. 99. 



line, secured to a hemp span between the bow and stern of 

 each boat. 



The length of the distance line is exactly equal to that of the 

 sweep wii'e; one boat runs the required transit, and the other 

 keeps the distance Hne taut. 



The kite wires are marked in fathoms, and the actual depth 



