he increasing
importance of the camera obscura as a photographic instrument makes it
desirable to bring together what is known of its early history, which is
far more extensive than is usually recognized. In southern climes, where
during the summer heat it is usual to close the rooms from the glare of
the sunshine outside, we may often see depicted on the walls vivid
inverted images of outside objects formed by the light reflected from
them passing through chinks or small apertures in doors or
window-shutters. From the opening passage of Euclid's _Optics_ (_c._ 300
B.C.), which formed the foundation for some of the earlier middle age
treatises on geometrical perspective, it would appear that the above
phenomena of the simple darkened room were used by him to demonstrate
the rectilinear propagation of light by the passage of sunbeams or the
projection of the images of objects through small openings in windows,
&c. In the book known as Aristotle's _Problems_ (sect. xv. cap. 5) we
find the correlated problem of the image of the sun passing through a
quadrilateral aperture always appearing round, and he further notes the
lunated image of the eclipsed sun projected in the same way through the
interstices of foliage or lattice-work.

There are, however, very few allusions to these phenomena in the later
classical Greek and Roman writers, and we find the first scientific
investigation of them in the great optical treatise of the Arabian
philosopher Alhazen (q.v.), who died at Cairo in A.D. 1038. He seems
to have been well acquainted with the projection of images of objects
through small apertures, and to have been the first to show that the
arrival of the image of an object at the concave surface of the common
nerve--or the retina--corresponds with the passage of light from an
object through an aperture in a darkened place, from which it falls upon
a surface facing the aperture. He also had some knowledge of the
properties of concave and convex lenses and mirrors in forming images.
Some two hundred years later, between A.D. 1266 and 1279, these problems
were taken up by three almost contemporaneous writers on optics, two of
whom, Roger Bacon and John Peckham, were Englishmen, and Vitello or
Witelo, a Pole.

That Roger Bacon was acquainted with the principle of the camera obscura
is shown by his attempt at solving Aristotle's problem stated above, in
the treatise _De Speculis_, and also from his references to Alhazen's
experi