CHAP. xxi.J SCHEME OF TRIANGULATION 479 



Z drops Beacons 10, 1 1, 12, 13, revisiting them in reverse order. 



Vessels then unite at Beacon 1, and on data for provisional 

 p^ot being made known by X, all vessels sound as detailed within 

 the area to be surveyed. 



First Evening, 



X anchors near Beacon 9, after putting assistant on board 

 Cromer Knoll and Outer Dowsing lightvessels. 



Y anchors between Outer Dowsing and Dudgeon hght vessels, 

 after putting an assistant on board Dudgeon light vessel. 



Z anchors north of Haisborough Hghtvessel, after putting an 

 assistant on board Haisborough Hghtvessel. 



Triangulation is carried out that evening as per diagram. 



Second Day. 



X, Y, and Z continue sounding, and pick up the assistants 

 at the lightvessels, Y and Z communicating with X, as con- 

 venient, then' triangulation data. 



Second Evening. 



X anchors near Beacon 9 as before. 



Y anchors in a central position between Beacons 1 and 9. 

 Z anchors near Beacon 1. 



Triangulation completed, and bearing and scale of beacon 

 triangulation completed that evening. 



The following day all three ships continue sounding after 

 communicating their data to X. X picks up assistant at 

 Cromer Knoll hghtvessel, and completes the final calculations, 

 transmitting the revised plot to Y and Z that evening, for which 

 piu-pose all three vessels occupy some prearranged central posi- 

 tions for the night. 



SECTION III. 

 PRELIMINAEY PEOCEDUIIE— OBTAININa THE SCALE. 



The general procedure when laying out a beacon triangula- 

 tion with three ships present would approximately be as follows : 



Referring to Fig. III., which for our purpose will serve as a 

 general illustration, the details can be adapted to meet varying 

 circumstances. 



