20098An ESSAY
fore the before-mention’d Perſpective will be an
Hour-Line of a Dial, drawn upon the Plane
H L M I, and whoſe Style is G F.
Hour-Line of a Dial, drawn upon the Plane
H L M I, and whoſe Style is G F.
The ſame may be demonſtrated of the Re-
preſentations of other Hour-Lines, which form
a Dial upon the Plane H L M I.
preſentations of other Hour-Lines, which form
a Dial upon the Plane H L M I.
We now proceed to lay down the beſt way of
determining the ſaid Repreſentations.
determining the ſaid Repreſentations.
Prob. I.
122. To draw Vertical Dials.
Draw the Line E O, thro’ E, the Foot of the
11Fig. 66. Style of the Horizontal Dial A B F D, equal
to the Length of the Style of the Dial to be
drawn, and making an Angle with the Meri-
dian C. XII, equal to the Plane’s Declina-
tion.
11Fig. 66. Style of the Horizontal Dial A B F D, equal
to the Length of the Style of the Dial to be
drawn, and making an Angle with the Meri-
dian C. XII, equal to the Plane’s Declina-
tion.
This Angle muſt be aſſum’d towards the
Point D, when the Plane’s Declination is South-
Eaſt, as here; towards F, when the Declination
is Weſtward; towards A, when it is North-Eaſt-
wardly; and towards B, when it is North Weſt-
wardly.
Point D, when the Plane’s Declination is South-
Eaſt, as here; towards F, when the Declination
is Weſtward; towards A, when it is North-Eaſt-
wardly; and towards B, when it is North Weſt-
wardly.
Now, thro’ the Extremity O of the ſaid Line,
draw the Line I H, perpendicular thereto; and
the Line C P, thro’ the Center of the Dial, pa-
rallel, and equal to E O; thro’ whoſe Extre-
mity, P, draw the Line P S, parallel to H I.
draw the Line I H, perpendicular thereto; and
the Line C P, thro’ the Center of the Dial, pa-
rallel, and equal to E O; thro’ whoſe Extre-
mity, P, draw the Line P S, parallel to H I.
Then, to make the Dial, draw the Line h i,
22Fig. 67. in which prick down the Diviſions of the
Line H I; and in the Point o, (which is the
ſame as O) raiſe the Perpendicular o p, equal to
the Length of the Style of the Horizontal Dial
A B D F. This being done; draw a Parallel,
h i, thro’ the Extremity of this Perpendicular;
on which, prick down the Diviſions of the
22Fig. 67. in which prick down the Diviſions of the
Line H I; and in the Point o, (which is the
ſame as O) raiſe the Perpendicular o p, equal to
the Length of the Style of the Horizontal Dial
A B D F. This being done; draw a Parallel,
h i, thro’ the Extremity of this Perpendicular;
on which, prick down the Diviſions of the