( « ) 
Art. VI . — Chart of the Island of Ascension , with Remarks on 
its Geognosy. (Plate III.) By Captain Robert Camp- 
bell, R. N: Communicated by the Author. 
HC HIS island, situated in the Atlantic Ocean, in South Lat. 
7° 55', West Long. 14° 51', is about nine miles in length from 
SE. to NW., and ’about five or six miles broad *. During the 
time of Buonaparte's confinement in St Helena, it was judged 
prudent to keep a small force there. For some time I had the 
command of the party, and employed myself in making a chart 
of the island, which 1 now communicate to the public. In the 
chart, the principal stations which served for its construction, 
and the more remarkable points, are marked 0. 
The angles of the chain of triangles which connect the sta- 
tions, were taken with a sextant ; and, as their sides were there- 
fore not on a horizontal plane, their inclinations were measured, 
and their horizontal projections found, by reducing the oblique 
lines in the proportion of radius to the cosines of their inclina- 
tion. 
The positions of the intermediate points were determined by 
observations made at the principal stations ; but it was not thought 
necessary to apply reduction to the sides of these secondary 
triangles, on account of their obliquity. 
The height of the Green Mountain (one of the stations), was 
found, by taking its elevation with the sextant and an artificial 
horizon, above a station on the sea-coast ; and the height of this 
station above the level of the sea was carefully measured. As 
the other mountains were too low to be seen from the sea-coast 
in the artificial horizon, their heights were found by taking, with 
the sextant, their angles of elevation at the several stations on 
the coast, above objects on a level with the eye, and in vertical 
planes passing through the eye and their summits. The level 
was determined by looking through a tube to which a spirit-level 
was fixed. 
* The Latitude was settled by a series of observations of the sun’s altitude, 
taken in an artificial horizon, when his northerly declination admitted of this be- 
ing done. The Longitude was settled by means of numerous lunar observations, 
agreeing with a series of observations of the eclipses of Jupiter’s moons, some of 
which were also observed at Greenwich. 
