APPENDIX. 



431 



cessive 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 

 oldest officer on the deck ; these angles, together with those made by 

 the visual tangents to the shores, 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. 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 horizontal 

 angles ; and at the same time, the altitude and azimuth of the mast of 

 one of the ships is observed for the purpose of defining their position. 



When this is done, one of the vessels changes her position, while the 

 others maintain theirs by manoeuvring so as to keep the angles between 

 objects on the shore of the same magnitude ; the boats having in the mean 

 time changed theirs also : the same operations are then repeated. 



Of such an operation, the annexed wood-cut is an example. 



Zly.2 



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 determined 



