Full text: Gravesande, Willem Jacob: An essay on perspective

on PERSPECTIVE. Mirrours muſt not be plac’d within the Machine; for
in ſuch a cloſe Place, ones Breath will ſully them; but
not the Convex Glaſs, becauſe it is encloſed in a


197. The Uſe of the Camera Obscura
in Deſigning.

Definition .

1. ACamera Obſcura is any dark Place, in which
outward Objects expoſed to Broad-Day-light,
are repreſented upon Paper, or any other white

The Way to repreſent Objects in the Camera
Obſcura, is to make a ſinall Hole in that ſide
thereof next to the Objects, and place a Convex-
Glaſs therein, then if a Sheet of Paper be ex-
tended in the Focus of the ſaid Glaſs, the Objects
will appear inverted upon the Paper.

198. Theorem I.

2. The Camera Obſcura gives the true Repreſen-
tation of Objects.

The Figures repreſented in the Camera Obſcura
are form’d (as is demonſtrated in Dioptricks)
by Rays which coming from all the Points of the
Objects, paſs through the Centre of the Glaſs: So that an Eye placed in the ſaid Centre, would
perceive the Objects by the ſaid Rays, which
conſequently by their Interſection with a Plane,
muſt give the true Repreſentation of the Objects. But the Pyramid which the ſaid Rays forms with-


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