scribe it here, so as to bring the method into notice, as well as to ex- 

 plain it more fully. 



METHOD OF SURVEYING THE CORAL ISLANDS. 



The basis of the method rested on the measure of distances by 

 sound. For this we had ready means, by firing guns alternately 

 from the different vessels, any three of which being stationary, the 

 distances and positions of objects could be determined from them by 

 direct angles, giving a double result, or by the angles between them, 

 taken from the shore, or from boats, furnishing data for the problem 

 of " the three points." When both methods can be applied at the same 

 time, it is evident that the utmost accuracy may be obtained. Upon 

 the land, by employing many observers, and occupying all the points 

 of a trigonometric survey simultaneously, the whole work might evi- 

 dently be completed in a very short space of time ; and in like manner 

 upon the water, creating by means of vessels and boats a number of 

 artificial stations around an island, measuring angles simultaneously at 

 them all, and base lines by sound, the rapidity with which a survey 

 can be performed is equally as great. 



By means of the system of signals prepared by me for the Exploring 

 Expedition, I could direct the vessels to assume any position I might 

 select as most fit for our purpose. When these were reached, general 

 but minute instructions directed the observations that were to be taken 

 at each, in doing which there was no difficulty. These observations 

 were entered upon a deck-board, for which the following form was 

 prescribed : 



FORM OF DECK-BOARD. 



On approaching the island to be surveyed, signal was made to pre- 

 pare for surveying duty ; if boats were to be used, the number of them 

 and the vessels whence they were to be despatched was next indicated ; 



