SURVEYS. 



and finally, the position each vessel was to occupy was shown. The 

 vessels having reached their assigned places hove-to, and the boats 

 having been previously despatched, would about the same time have 

 anchored in their assigned stations, at the points of reefs, and hoisted 

 their appropriate signals. The vessel that is first to fire a gun then 

 hoists an ensign at the foremast-head, which is answered by all, and 

 the flag is in like manner displayed previous to each successive fire. 

 The firing then goes on in quick succession from all the vessels ; and 

 at the time, all the officers being on deck for the purpose, angles are 

 measured between the other vessels and objects on the shore, each by 

 a different observer, as directed and indicated by the senior officer pre- 

 sent ; these angles, together with those made by the visual tangents to 

 the shore, have always been found sufficient to plot from. During this 

 operation the ensign is kept hoisted at the peak, so that all the angles 

 may be taken simultaneously ; and at the same time, the altitude and 

 azimuth of the masts of the ships is observed from the boats, for the 

 purpose of determining their position more accurately. Altitudes of 

 the sun for time, and angles whence to calculate the azimuth of some 

 one of the objects, are also taken immediately before or after the hori- 

 zontal angles. 



When the duties at the first station have been finished the vessels 

 and boats change positions alternately, and at each change the same 

 operations are repeated. 



To illustrate still further the mode in which the whole squadron was 

 made to concur in obtaining unity of action, a detail of a survey and 

 a plot of the work are given on Plate 1, Fig. 1. 



By these alternate changes in the stations of the several vessels and 

 boats, continued until a circuit of the island has been made, the work 

 is finished, and when it joins, it is proved by the last distance deter- 

 mined by azimuthal angles and base by sound, as for a base of verifi- 

 cation. The deck-boards are then sent on board the flag-ship, where 

 the work is calculated and plotted. 



The survey of the island thus represented, which is about seven 

 miles in length, was performed in three hours and thirty-five minutes. 

 It began, as noted on the deck-boards, at 1*18 p. m., and the observa- 

 tions closed at 4*53 p. m. 



The facility with which the operations are made can scarcely be con- 

 ceived until they are witnessed, and I may add the accuracy, not less 

 so when the proper steps are taken to carry all parts into operation. 



