CHAP. XXI.] OBTAINING THE SCALE 483 



Figure VI., Case 2. 



With two ships, X and Y, available only as in Fig. VI., 

 the procedure would be something as follows : 



Y drops Beacon 1 and X drops Beacon 2 on the prearranged 

 bearing, approximately 2 miles from 1, X being controlled for 

 distance by Y, who remains under way near 1, whilst observing 

 masthead angle of X. 



Y then takes up a position at anchor by the aid of Beacons 

 1 and 2, approximately f mile from 1, and in a direction at right 

 angles to that of the beacons. X next drops Beacon 3 on the 

 opposite Une of bearing, the distance being controlled from Y 

 at anchor, who will communicate her position to X, if required, 

 by cruiser arc lamp, or other suitable means, whilst X is pro- 

 ceeding from Beacon 2. 



On Beacon 3 being dropped, approximately 2 miles from 

 Beacon 1, X takes up a position under way about 1| miles 

 from Y, and on the opposite side of Beacon 1, as in Fig. V., 

 when a similar procedure will be adopted for obtaining the 

 scale as previously described. 



It wiU be seen that X and Y now occupy the best positions 

 for determining the distance between Beacons 2 and 3, 4 miles 

 apart — the receiving angle at these beacons between the two 

 ships being approximately 45°. 



Case III. 



Should one ship only be engaged, the procedure would be 

 generally the same as in Fig. VI., a boat containing at least 

 two assistants being substituted for the ship Y. 



Note. — That side of the beacon where the light or back- 

 ground is best for observing X should be selected by the ship 

 or boat when taking up her position. 



SECTION IV. 

 EXTENDING THE TRIANGULATION. 



In continuation of Section III., and referring again to 

 Fig. III., which wiU serve as a general Illustration of our pur- 

 pose, the general procedure would be something as follows: 



On completion of the last set of simultaneous observations 



