215110An ESSAY
20.
Concerning what hath been ſaid of the
Picture being parallel, it muſt be obſerv’d, that
in the precedent Demonſtration, the Angle of
Inclination of the Picture in this Demonſtration
is meaſur’d next to the Objects; and if this An-
gle be diminiſh’d till it become nothing, we
ſhall have a Picture parallel to the Horizon un-
derneath the Eye. But, by the Demonſtration,
the Inclination of the Mirrour being half the In-
clination of the Picture, it follows, that the In-
clination of the Mirrour is alſo equal to nothing,
and conſequently it ought to be likewiſe parallel
to the Horizon. In the ſame manner we de-
monſtrate, that the Looking-glaſs muſt be verti-
cally ſituated, when we conſider the Picture pa-
rallel above the Eye: For to give this Situation
to the Picture, the Angle of the Inclination of
the Picture meaſur’d next to the Objects, muſt
be augmented till it be 180 Degrees, whoſe half
90 Degrees is conſequently the Inclination of the
Mirrour.
Picture being parallel, it muſt be obſerv’d, that
in the precedent Demonſtration, the Angle of
Inclination of the Picture in this Demonſtration
is meaſur’d next to the Objects; and if this An-
gle be diminiſh’d till it become nothing, we
ſhall have a Picture parallel to the Horizon un-
derneath the Eye. But, by the Demonſtration,
the Inclination of the Mirrour being half the In-
clination of the Picture, it follows, that the In-
clination of the Mirrour is alſo equal to nothing,
and conſequently it ought to be likewiſe parallel
to the Horizon. In the ſame manner we de-
monſtrate, that the Looking-glaſs muſt be verti-
cally ſituated, when we conſider the Picture pa-
rallel above the Eye: For to give this Situation
to the Picture, the Angle of the Inclination of
the Picture meaſur’d next to the Objects, muſt
be augmented till it be 180 Degrees, whoſe half
90 Degrees is conſequently the Inclination of the
Mirrour.
Prob. II.
22.
To repreſent Objects, ſo that what appears on
the right Hand, ought to be on the left.
the right Hand, ought to be on the left.
23.
Having placed the Box X, in the Situation
11Fig. 70. as per Figure, the Door B muſt be opened, and
the Aperture N ſhut; then putting the Mirrour H
in the Diſpoſition mentioned in Numb. 11. raiſe
up the Mirrour L towards the Top of the Box;
and incline it towards the firſt Mirrour, in ſuch
manner that it makes an Angle with the Hori-
zon of 22 {1/2} Degrees; that is, that the Top of the
Machine, after a double Reflection, appears ver-
cal in the Mirrour H.
11Fig. 70. as per Figure, the Door B muſt be opened, and
the Aperture N ſhut; then putting the Mirrour H
in the Diſpoſition mentioned in Numb. 11. raiſe
up the Mirrour L towards the Top of the Box;
and incline it towards the firſt Mirrour, in ſuch
manner that it makes an Angle with the Hori-
zon of 22 {1/2} Degrees; that is, that the Top of the
Machine, after a double Reflection, appears ver-
cal in the Mirrour H.
24.
Now if Objects are to be repreſented for
the Picture inclin’d, the Mirrour L muſt make
the Picture inclin’d, the Mirrour L muſt make