20199on PERSPECTIVE.
P S, and making the Point p be the ſame as P.
then join each Diviſion of this Line, to the
correſpondent Diviſion of the Line h i; and the
Dial ſought, will be drawn: p being the Foot
of the Style, and p s the Horizontal Line.
then join each Diviſion of this Line, to the
correſpondent Diviſion of the Line h i; and the
Dial ſought, will be drawn: p being the Foot
of the Style, and p s the Horizontal Line.
Demonstration.
The Baſe Line is h i;
p s is the Horizontal
11Fig. 66,
67. Line; p the Point of Sight; and E O, or C P,
of Figure 66. is the Length of the principal
Ray.
11Fig. 66,
67. Line; p the Point of Sight; and E O, or C P,
of Figure 66. is the Length of the principal
Ray.
Now, ſuppoſe the Plane p s h i, to be ſet per-
pendicularly upon the Horizontal Dial, in ſuch
manner, that the Line h i coincides with H I,
and the Point o with O. Suppoſe, moreover,
that thro’ the Extremity of the Style, which we
conſider as the Eye, Lines are drawn in the Ho-
rizontal Plane, parallel to the Hour-Lines of
the Dial; it is evident, that theſe Lines will
meet the Horizontal Line p s, in the Point al-
ready prick’d down; and conſequently , 2213. Appearances of the Hour-Lines, are the Lines
joining the Diviſions of the Lines h i and p s.
pendicularly upon the Horizontal Dial, in ſuch
manner, that the Line h i coincides with H I,
and the Point o with O. Suppoſe, moreover,
that thro’ the Extremity of the Style, which we
conſider as the Eye, Lines are drawn in the Ho-
rizontal Plane, parallel to the Hour-Lines of
the Dial; it is evident, that theſe Lines will
meet the Horizontal Line p s, in the Point al-
ready prick’d down; and conſequently , 2213. Appearances of the Hour-Lines, are the Lines
joining the Diviſions of the Lines h i and p s.
Remark.
If the Line H I happens to meet the Meri-
dian; the common Method, by the Horizontal
Dial, is eaſier than this.
dian; the common Method, by the Horizontal
Dial, is eaſier than this.
Prob. II.
123. To draw inclining Dials.
Theſe Dials are drawn in the ſame manner as
Vertical ones; the following Preparations being
firſt made.
Vertical ones; the following Preparations being
firſt made.