een larger and
unreversed. This is much the same as Cardan's method published eight
years earlier, but though more detailed is not very clear. He then notes
the application to portraiture and to painting by laying colours on the
projected images. Nothing is said about the use of a lens or of solar
observations. The second edition, in which he in the same words
discloses the use of a convex lens in the aperture as a secret he had
intended to keep, was not published till 1589, thirty-one years after
the first. In this interval the use of the lens was discovered and
clearly described by Daniello Barbaro, a Venetian noble, patriarch of
Aquileia, in his work _La Pratica della perspettiva_ (p. 192), published
in 1568, or twenty-one years before Porta's mention of it. The lens used
by Barbaro was an ordinary convex or old man's spectacle-glass; concave,
he says, will not do. He shows how the paper must be moved till it is
brought into the focus of the lens, the use of a diaphragm to make the
image clearer, and also the application of the method for drawing in
true perspective. That Barbaro was really the first to apply the lens to
the camera obscura is supported by Marius Bettinus in his _Apiaria_
(1645), and by Kaspar Schott in his _Magia Universalis_ (1657), the
former taunting Porta with the appropriation.

In an Italian translation of Euclid's _Optica_, with commentary,
Egnacio Danti (1573), after discussing the effects of plane, convex and
concave reflectors, fully describes the method of showing reversed
images passing through an aperture in a darkened room, and shows how, by
placing a mirror behind the aperture, unreversed images might be
obtained, both effects being illustrated by diagrams. F. Risner, who
died in 1580, also in his _Opticae_ (1606) very clearly explained the
reversal of the images of the simple camera obscura. He notes the
convenience of the method for solar observations and its previous use by
some of the observers already mentioned, as well as its advantages for
easily and accurately copying on an enlarged or reduced scale,
especially for chorographical or topographical documents. This is
probably the first notice of the application of the camera to
cartography and the reproduction of drawings, which is one of its
principal uses at the present time. In the _Diversarum Speculationum
Mathematicarum el Physicarum_ (1585), by the Venetian Giovanni Battista
Benedetti, there is a letter in which he discusse