43
5. Then from W to each of these points in the arc
WNABS draw lines, and the points of intersection of these
lines on the line SN produced, will give the diameters of
as many parallels of latitude as are necessary; that is, 12,
for there are no more visible about the horizon.
6. The circular parallels of latitude have not a common
centre, therefore the diameter of each parallel must be
bisected, and the 12 circles of latitude described through
the points of corresponding degrees, as 80, 70, 60, &c., the
centre of 80° being the pole; but that of all the others in
some point beyond P and N.
' 67. Problem II. To draw the meridians.
1. Through the three points W, P, E, describe the circle
CPO, as the plane of projection. Delineate on this plane
the meridians for a stereographic projection, by some of
the foregoing methods. Each of these meridians must
pass through the pole P till it comes in contact with the
semicircle WNE, otherwise the map will be deficient in
the meridians that stretch beyond the pole.
2. Thus, in describing the meridian EP, the circle is
continued to Gf. In the meridian HP, the circle is con
tinued to the point between Gr and A, and so on of all the
others. Thus the meridional projection becomes the basis
of the horizontal. Hence the following very elegant and
convenient method of operation.
68. Problem III. By describing the horizontal 'projection
first, to complete a horizontal projection for the latitude of
London. (Fig. 30, No. 2.)
69. First, to draw the meridians.
1. CPD is the primitive circle, CD the equator, PS the
first meridian or north and south azimuth. From D to E
in the quadrant PD, and from C to W in the quadrant
CP, set off 51° 30' for the latitude of London, and draw
the line WE, which will be the east and west azimuth of
the place.
2. The point of intersection of the line WE, with the
first meridian NPS, represents London marked Z, from
which, as the centre of projection with the radius ZE, de
scribe the plane of projection NESW, which will represent
the horizon of London,
