19997on PERSPECTIVE.
Points be found , the Repreſentations of 11109,
115, 117. Shadows will be had.
115, 117. Shadows will be had.
CHAP. IX.
The Uſe of Perſpective in Dialling;
ſhewing
how to draw the Hour Lines upon any
Kind of Plane, by means of an Horizon-
tal Dial.
how to draw the Hour Lines upon any
Kind of Plane, by means of an Horizon-
tal Dial.
PERSPECTIVE is not only uſeſul in
drawing, but likewiſe in other Parts of Ma-
thematicks, and principally in Dialling: For if
the Extremity of the Style be conceived as the
Eye, and the Sun’s Rays as viſual Rays, all
poſſible Kinds of Dials may be drawn for the
ſame Latitude, by Means of an Horizontal Dial,
as we are now going to ſhew,
drawing, but likewiſe in other Parts of Ma-
thematicks, and principally in Dialling: For if
the Extremity of the Style be conceived as the
Eye, and the Sun’s Rays as viſual Rays, all
poſſible Kinds of Dials may be drawn for the
ſame Latitude, by Means of an Horizontal Dial,
as we are now going to ſhew,
121.
Let A B C D be an Horizontal Dial
made for any given Latitude; E F its Style, and
22Fig. 65. H I M L a Plane, upon which a Dial is to be
drawn. Now if this Plane be ſo ſituated, that
the Extremity of its Style F G, coincides with
the Extremity of the Style of the Horizontal
Dial; and if the Perſpective of one of the Hour
Lines of the Horizontal Dial A B C D, be found
upon the Plane H I M L, in conceiving the
Point F as the Eye, it is evident , that 332. Shadow of the Point F, will fall upon the ſaid
Perſpective, at the ſame Time that it falls
upon the Hour Line, whereof it is the Per-
ſpective; and conſequently, the ſaid Shadow
will ſhew the ſame Hour upon the Plane H I M L,
that it ſhews upon the Horizontal Dial:
made for any given Latitude; E F its Style, and
22Fig. 65. H I M L a Plane, upon which a Dial is to be
drawn. Now if this Plane be ſo ſituated, that
the Extremity of its Style F G, coincides with
the Extremity of the Style of the Horizontal
Dial; and if the Perſpective of one of the Hour
Lines of the Horizontal Dial A B C D, be found
upon the Plane H I M L, in conceiving the
Point F as the Eye, it is evident , that 332. Shadow of the Point F, will fall upon the ſaid
Perſpective, at the ſame Time that it falls
upon the Hour Line, whereof it is the Per-
ſpective; and conſequently, the ſaid Shadow
will ſhew the ſame Hour upon the Plane H I M L,
that it ſhews upon the Horizontal Dial:
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