206 APPENDIX. 



In the second class we considered all the minor fixed points 

 wliich were included in the triangulation, excepting the details of the 

 coasts and ' boundary lines,'* which belonged to the tliird class. 



We supposed that the ship had sailed from the ' first' harbour. f At 

 six, in the morning, (marked 6) the position of the vessel was fixed 

 by two or more angles between marks, already fixed, upon the land. 

 At 6'30, and at 7 similar means were used to fix the ship's place. 

 Soundings were taken, and laid down by proportioning to the times 

 of each sounding, the portions of distances run between the two 

 stations, as shewn by patent log, by bearings of a mark, such as 

 6 (in the figure) while sailing from 6 30 to 7 : by independent 

 double angles, (two angles between three marks), orliy simple cross- 

 bearings. 



Transit bearings were always sought for, by compass as well as by 

 noting when marks were ' on ;' or, in a line, one with another, with- 

 out reference to the compass. We endeavoured to ascertaiii (or fix) 

 the ship's position at the same moment, by the most available of the 

 numerous methods so readily occurring Mobile the log was going, the 

 time noted carefully (as often as angles or bearings were taken), 

 and several first class marks in sight. Transit bearings were useful 

 in the details of the coast line, as may be seen by the lines dra^vn 

 from 6-30, 7 and 8 ; and they corroborated the correctness of the 

 triangulation, when applied to first and second class marks. 



By a judicious selection of objects, and a clever application of 

 transit bearings, I have seen extensive and correct triangulations 

 carried on from data, obtained at sea, which appeared uttei-ly in- 

 adequate. | I do not imply that the absolute position of any one 

 point was independently correct, because all depended at first upon 

 observations at sea ; but tkat the points of the triangulation were all 

 so correct, relatively, that, upon after examination, when the regular 

 routine of harbour work had been combined with the data obtained 

 afloat, and their truth ascertained by connection with the previous 

 observatory, no alteration was found necessary. 



Perhaps I should explain, that in the plan of the ' first ' harbour 

 all depended upon the base Ab ; by which also were fixed B and C. 

 From the summits B and C ; — G, D, E, F, were fixed, as well as a 



* By ' boundary lines ' [ mean limiting outlines of shoals, or rocky 

 place?. f See figure, t By Mr. Stokes. 



