10 



HYDROGRAPHY. 



by an independent set of observations, including meridian distances, 

 latitudes, bases by sound, and distances from heights, the whole proved 

 and rectified by final observations, made when passing around the 

 Group, and after the charts had been constructed ; by this means I 

 felt confident that few errors had escaped us, and that the work was 

 complete. 



The explanation of the manner of conducting the surveys of the 

 rivers will also admit of a few remarks. 



In the survey of a river, it is very important that the officers acting 

 in boats should understand the part they are required to perform. The 

 survey of a river by a regular and slow triangulation is a very simple 

 affair. The skeleton charts are prepared from the triangulation s, and 

 the hydrographical part is filled in by a small force : this requires much 

 time, and that, it is well known, was not at my disposal ; therefore 

 it became necessary that the duties should be conducted quickly, 

 and, while the work was in progress, that it should be immediately 

 plotted and compared, as each day's work was finished. A mistake 

 or error was a loss not only of our time, but necessarily of much 

 labor to rectify it : to avoid this, as far as possible, the operations 

 were conducted so as to triplicate the results or observations; which 

 operated as checks and proofs on all the work. In the survey of the 

 Columbia we had eight boats, manned by the officers and men of the 

 Peacock, after her wreck, and the Porpoise ; six of the boats were di- 

 vided into two divisions, one to take the starboard side of the river, and 

 the other the port side, or what I termed the alphabetical and numerical 

 sides, as distinguished by the signals so marked. The leading boats 

 placed the signals and observed the back angles ; the centre boats fol- 

 lowed, and observed the forward and backward angles, and the rear 

 boats observed the forward angles, and all fired guns for bases. The 

 boats of either division never changed sides, consequently all the 

 stations the one division occupied were numerical, while those of the 

 other were alphabetical ; thus, moving on almost simultaneously, being 

 well aware of the character of the signals, and fully understanding 

 their positions, no impediment was suffered to interfere with the pro- 

 gress of the work. The remaining two boats observed the astrono- 

 mical bearings from one distant station to another, sketched in the 

 shores, and, as frequently happened, engaged in the triangulation; 

 and when about to pass a bend in the river, they occupied the neces- 

 sary additional stations. Further facilities were afforded by the brigs 



