APPENDIX NO. X. 
403 
between the sun's centre and the object was measured, and the corre¬ 
sponding time noted. For this purpose the smaller telescope was used, 
and sometimes a pocket-sextant. Whenever the object, the azimuth of 
which was to be found, was farther removed than 120° from the sun, 
the angular distance of an intermediate object, about 90° from the sun, 
was introduced. At the same time the altitude of the sun was observed, 
to allow for the reduction of the arc of the horizon: this reduction was 
always small, since the sun was seldom higher than 30°, and in no case 
higher than 36°. 
When the azimuth of an object was thus determined, a number of 
other conspicuous objects were connected with it by horizontal angles. 
Two determinations of the azimuth of an object, obtained from two 
astronomically-determined points, seldom differed more than seven 
minutes. 
The principal points of the coast have thus become known, cither by 
direct observations of latitude and longitude, by latitude and a solar 
bearing, or by the intersection of two azimuths, according to methods 
explained above. 
The filling in of the minor or secondary points remains yet to be 
explained. Their position was generally obtained by solar or compass 
bearings and estimated distances. In regard to the solar bearings, it 
may be remarked that their frequent application rendered the construc¬ 
tion of a table of double entry for every degree of altitude of the sun 
from 5° to 36°, and for every degree of angular distance from 10° to 
125°, quite an acceptable improvement in facilitating the reduction. 
In regard to magnetic bearings, it is to be remarked that they were 
taken with a pocket-compass, the face of which, divided into degrees, 
was fastened to the bottom of the box to allow the needle free play. 
The magnetic declination (variation of compass) observed with this 
instrument at different times at the same place seldom differed more than 
three degrees, while, on the contrary, other compasses, with the card 
fastened to the needle, would remain stationary in any position in which 
they were placed, in consequence of the small horizontal force in the 
region traversed. Care was taken to keep the compass perfectly level, 
and in sighting, the eye was kept directly over the north end of the 
needle. 
The estimation of distances of intermediate points was the only thing 
loosely obtained; but it must be remembered, however, that these dis¬ 
tances were always checked by means of astronomically-determined 
positions, and hence no error of this kind, although they were of fre¬ 
quent occurrence, could be propagated. Distances estimated at the 
