CHAP. \ II.] COAST-LINING 193 



or delineating the outer edge of the reef Subsidiary marks 

 can be made at other points, as x, y, z, and fixed by angles 

 from h, d, etc., with distances measured by the angle of the 

 line. 



The shore line can either be sketched by A, as he walks 

 from station to station ; or can be put in afterwards, if greater 

 correctness is required, using the ordinary ten-foot pole to fill 

 in between a, b, c, etc. 



If a theodolite is used, which it is well to do in a case where 

 we have not been able to get any measured base at all, and 

 must consequently work back to a, it must be set up first at 

 a, and the angle to b taken from some fixed object, whose true 

 bearing we should obtain, as we in this case must not be 

 dependent on the compass. B Avill be at b with his line, and 

 when A has finished, will walk on to c, so that A, when he 

 arrives at b, can take the angle from a as zero to c. With a 

 theodolite, then, A must visit every station, unless B has one 

 also. 



At every new position, the last A will be used as zero. 



The readiest way for B to direct his line so as to be at right 

 angles is to use the so-called " cord-triangle," which is simply 

 a triangle formed of a piece of line whose sides are in the 

 proportion of 3, 4, 5, the angles being marked by knots. When 

 stretched on the ground, with the corner between 3 and 4 at 

 the A, and the 4 side coincident with the direction of the 

 other A, the direction of the 3 side is at the right angle 

 required. Any similar contrivance will serve the purpose. 



Note. — This method was largely used by Lieutenant W. U. Moore in the 

 survey of the Fiji Islands, and is a good example of the dodges that have to 

 be improvised to meet circumstances 



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