3IO DISCOVERY REPORTS 



mile to give a sharp movement when they are in contact, and (iv) a sufficient distance 

 between and clear view of the leading beacons to ensure a steady course. These were 

 all present to a sufficient degree in this instance. 



Owing to the configuration of the land, it was found that the usual methods were 

 impossible. The following method was therefore devised, and, although perhaps not 

 rigorously accurate, is sufficiently so to make its employment worth while. 



Theodolite angles were taken, with more than usual repetition to ensure accuracy, at 

 C, D, E and F (see Fig. 2). The distance CD had been calculated direct from the 

 measured base DG, through two triangles, and agreed to within a foot or so of 1480 ft. 

 From the triangle CDE, the angles of which had been measured, DE was calculated, and 

 then DH (3414-1 ft.) by dropping a perpendicular from E to FD at H. From DE in the 

 triangle already found, FD was calculated to be 9435-1 ft. ; by subtracting DH from DE 

 a distance of 6o2i-oft. was obtained for HE. So far everything had been straight- 

 forward. Unfortunately HF could not be the real measured mile, as F was on land and 

 also was backed at about 5 ft. from the sea by a perpendicular precipice giving no room 

 for a rear beacon, but it was the only spot from which all the other main stations neces- 

 sary could be seen. 



A point N farther along the coast to the eastward of F was suitable, as it had a flat 

 rocky ledge behind it for 70 ft., which was sufficient for the distance between front and 

 rear beacons. A careful angle was taken to a mark placed here and the distance was 

 measured, this being the hypotenuse of the small triangle FNO . The distance FO was 

 the distance to be added to HF for the actual total between the two pairs of beacons. 



Then the ' Alert ' was run out from A'^ for a couple of hundred feet, and a point mentally 

 marked on the beach at Stromness (a red hut, quite conspicuous) near D for the real line, 

 this being as nearly as possible parallel to FD. On adding 99-3 ft. to the distance HF, 

 this being FO the resultant of the angle, etc. to the real marks at A^, it was found that the 

 mile (or the beacons) from the selected positions, chosen as they were by rough measure- 

 ment, was 33 ft. too long. Then, as the outer beacon at N could not be shifted, the 

 inner beacon at E was moved a carefully measured distance of 33 ft. towards N . The 

 setting up of marks for the rear beacons in each case was fairly simple, as a sextant 

 was all that was required, with a man moving a small mark until it coincided with the 

 correct position with the sextant at 90° . For the rear leading mark we simply carried a baulk 

 of timber up country as far as we could, and with the hut as the foresight, set it up so 

 that the approximate place off A^ was in line. It was then planted and painted white {Y). 



Although this method cannot be called rigorously accurate, I think it will be found 

 sufficiently near, and in the circumstances was the only one that appeared practicable. 



FD 9435-1 ft. 

 DH -3414- 1 ft. 



.'. HF 6021-0 ft. 

 FO 99-3 ft. 



HO 6120-3 ft. 



