CHAP. VI.] RUNNING SURVEY 183 



an intersection at Breastmark I. of five lines — viz., from III., 

 II., the intermediate fixes, and from I. 



Plot the corner fixes and lay off all angles to secondary points. 



All points being down, the soundings can be fixed and coast- 

 line and topographical features sketched in, getting additional 

 angles when necessary. 



It is desirable to use two deck-books, entering all angles 

 for each alternate fleet in one or the other. The plotting can 

 then go on in the chart-room, while the angles for the next 

 fleet are being obtained and recorded. 



It is necessary to remember that on obtaining the true 

 bearing of an object a long way ahead, such object is 

 eventually plotted on that line. 



If care be taken over the details described, the objects 

 should plot very closely, when the tide is not too strong, and 

 precautions are taken not to run the bases when the streams 

 are changing. 



All angles taken near a beacon should be reduced to the 

 position of that beacon, the bearing and distance of it having 

 been noted for that purpose. The reduction is readily effected 

 by writing the angles down as if they had been taken with a 

 theodolite, and using the method explained on p. 91. 



At the extremities of such a survey as this shore observa- 

 tions should be obtained, if possible. From these positions and 

 from the true bearings obtained corrections to scale and bear- 

 ing can be made as already explained on p. 108. 



In calculating the length of the different patent log bases 

 the following formula should be used : 



t{h~a) 



X= ^ ,- 



t + t' 



Where X is the current in time t with the stream, 



a is distance shown by the log with the stream, 

 6 is distance shown by the log against the stream, 

 t' is time occupied in run against the stream. 



From X the true distance can be deduced. 



The survey of the coast of Zululand, 200 miles in extent, 

 carried out on these principles on a scale of half an inch to the 

 mile, was found to agree precisely with the results of the 



