CAMERA OB S CUR A.
THIS example is clofely allied to the principles ad-
vanced in Lecture I. 2d feries, and explains the re~
verfion of external objects. Thus a is the counterpart
of A, but reverfed by paffing through the crevice j b is
the counterpart of B, and c of C.
This is alfo a very entertaining philofophical amufe-
ment: we mall, for the information of our readers, in-
fert the moft authentic manner of performing it, as it re-
quires no further apparatus than merely a lens glafs in
a fcioptric ball.
1. The Camera Obscura, or darkened room, is,
any large room or chamber made as dark as poffible, fo
as to exclude all light but that which is to pafs through
the hole and lens in the ball fixed in the window of the
The following particulars are to be attended to in thist
philofophical contrivance. Firir, That the lens be ex-
tremely good, or free from any veins, blebs, &c. which
may diftort and blemifh the picture.
2dly, That the lens be always placed directly againfl
the object whofe picture you would have perfectly formed
to contemplate; for if the glafs has any other pofitionto
the object, the image will be very imperfect, indiftincr,
and confufed. ,
U 2 3dly,