Cape Coast or Sierra Leone. I made the variation 22°* 17' W.
I could only afford to furnish myself with KaterV pocket azimuth
compass for this observation, but I took the precaution to determine
its error (2°) at the observatory. The azimuth circle at the
foot of my reflecting circle, having a nonius by which it may be
read within a minute, I preferred bringing down and determining
the distance of the sun from any remarkable object in the horizon
at each observation, and bearing that object leisurely afterwards,
to bearing the sun itself at each observation, having no assistant,
and the compass being graduated only to degrees.
I had the reflecting circle made, to use occasionally on a foot,
like a repeating circle with a moveable level, to obviate the
inconvenience of being unable to take meridian, or indeed double
altitudes of the sun, with an instrument of reflection in those
parts of the interior of Africa approaching the equator, since in
using the artificial horizon, the sextant will not measure an
altitude exceeding 60°. It is rather hard upon a traveller to be
obliged to keep awake to watch the culmination of a star, after
being worn out by a hard day’s march. Baron de Humboldt
proposes placing the index glass at an angle, say 30°, to the false
horizon glass’, which I have done to an old wooden sextant which
I keep in reserve; but I do not see how it is to be rectified from
time to time in a close inland country, where the whole circle of
the horizon is rarely visible, unless by another instrument
M r Beauchamps' submits the plan of inclining a glass 45°, on the
artificial horizon, which would enable the observer to measure the
greatest possible attitude, but I confess I do not immediately see
how the angle of inclination could be verified from time to time
with facility; and it must always be recollected that measuring
the meridian ór correspondent altitude of a star by means of an
’ Voyage Partie Astronomique, 2 vol. 4to. vol. I. p. 9.
’ Mémoires sur iEgypt, t. II. p. 109. ,
artificial horizon, can never be a very nice observation, unless a
man be blessed with the tact of De Humboldt. The difficulty of
not seeing the hairs of the telescope of the circle when a star was
brought within the field, and the inconvenience of affixing a lamp,
is remedied by making the horizontal hair sufficiently thick to
eclipse the star when brought behind it. This instrument, and
a telescope for eclipses and occultations, I am proud to say, I owe
to the generous interest of my friends in the University of Cambridge.
I made the Consul’s house in Funchal 32° 38' 22" N. and
16° 53' 34" W. by the mean of several lunar distances. Unfortunately
I could not afford a chronometer, but this inconvenience
may in some degree be obviated at the expense of time and labour,
as I hope to prove in my next publication. It is but prudent,
however, to wish, and endeavour to be as sparing as -possible of
both, when travelling in the interior of Africa. “ Lorsqu’un
gouvernement ordonne une de ces expéditions qui contribuent à
la connaissance exacte du globe, et â l’avancement des sciences
physiques, rien ne s’oppose à l’exécution de ses desseins. Il n’en
est pas de même, lorsqu’un simple particulier entreprend à ses frais,
un voyage dans l’interieur d’un continent*.”
* De H um boldt, Voyage, vol. 1, 8vo. p. 63, 64.
T