Instrument for finding the true Lunar Distance. 63 
Cape Horn is confined to a channel, which is widened towards the 
south in proportion to the latitudinal breadth of the column, that is 
rushing to the east. Near the southern borders of this channel, the 
easterly winds commence, returning in eddies towards the west 
whence they are again carried eastwardly, in the current that rushes 
around Cape Horn. 
Art. VI.—Plan of an Instrument for finding the true Lunar Dis- 
tance ; invented by M. F. Maury, Passed Midshipman, U.S. Navy. 
GF HE, isa great circle of brass, standing upon three legs X y Z; 
it represents the horizon. AE, AF and BC, are arcs of great cir- 
cles; they also are of brass, and their planes pass through O, a com- 
mon centre. 
The periphery of GF HE, the middle curvature PQ, of AE, 
the concave circumference of BC, and the convex of A F, have 
equal radii centering in O. 
AE, describes half of a ee anere on the hinge at A, the axis of 
which, is that of the zenith and nadir, and of course passes through O. 
The extremity F, of the arc AF, is fixed in the plane of GF H E, 
and the extremity E, of A E, revolves in the plane of G F H E, and 
along its circumference, describing arcs of equal circles, from the 
centre O, until it stands in the plane of A F, the two then represent 
asemicircle. By means of the screw S, which presses E toG FH E, 
E is placed and,fixed at any distance from F. The hinge at A, is of 
brass turning against steel, which lessens friction. — 
AE and AF, are arcs of the azimuth circles, in which the sun or 
a star and the moon are at the time of taking a lunar observation. 
Each is 90° and graduated to every 10’ or 15’ on a slip of finer met- 
al, let in for that purpose. 
BC, is an arc of the geocentric circle, in the plane of which, the 
sun and moon appear, when the observation is taken ; it is graduated 
as the other arcs are, but from 20° to 120°. It is intended first to 
set off the apparent, and then to measure the ¢rue lunar distance. 
To assist in transferring the altitudes and distance with exactness, from 
the sextants with which they are taken, to the arcs of the instrument, 
each of them is provided with a vernier scale, a, b, c, having a tangent 
and a fixture screw respectively attached to them. ‘The extremity 
m, of BC, is hinged to zero of the vernier c; the axis of this hinge 
