106

CAMERA OBSCURA

Vitruvius, with commentary by Cesare Caesariano, one of the
architects of Milan cathedral, published at Como in 1521, shortly
after the death of Leonardo, and some twenty years before
Porta was born. He describes an experiment made by a
Benedictine monk and architect, Dom Papnutio or Panuce, of
the salm kind as Leonardo's but without the demonstration.

About the same time Francesco Maurolico, or Maurolycus,
the eminent mathematician of Messina, in his Theoremata de
Lumine et Umbra, written in 1521, fully investigated the optical
problems connected with vision and the passage of rays of light
through small apertures with and without lenses, and made
great advances in this direction over his predecessors. He was
the first correctly to solve Aristotle's problem, stated above,
and to apply it practically to solar observations in a darkened
room (Cosmographia, 1535). Erasmus Reinhold has described
the method in his edition of G. Purbach's Theoricae Novae
Planetarum (1542), and probably got it from Maurolycus. He
says it can also be applied to terrestrial objects, though he only
used it for the sun. His pupil, Rainer Gemma-Frisius, used it
for the observation of the solar eclipse of]anuary 1544 at
Louvain, and fully described the methods he adopted for making
measurements and drawings of the eclipsed sun, in his De Radio
Astronomico el Geometrico (1545). He says they can be used for
observation of the moon and stars and also for longitudes. The
same arrangement was used by Copernicus, Tycho Brahe, by
M. Moestlin and his pupil Kepler - the latter applying it in 1607
to the observation of a transit of Mercury - also by ]ohann
Fabricius, in 1611, for the first observations of sun-spots. It is
interesting to note this early employment of the camera obscura
in the field of astronomical research, in which its latest achieve-
ments have been of such pre-eminent value.

The addition of optical appliances to the simple dark chamber
for the purpose of seeing what was going on outside was first
described by Girolamo Cardan in his De Subtilitate (1550), as
noted by Libri. The sun shining, he fixed a round glass speculum
(orbem e vitro) in a window-shutter, and then closing it the images
of outside objects would be seen transmitted through the
aperture on to the opposite wall, or better, a white paper screen
suitably placed. The account is not very clear, but seems to
imply the use of a concave mirror rather than a lens, which
might be suggesled by the word orbem. He refers to Maurolycus'
work with concave specula.

We now come to Giovanni Battista della Porta, whose account
of the camera obscura in the first edition of the Magia Naturalis,
in four books (1558, lib. iv, cap. 2), is very similar to Caesariano's
- a darkened room, a pyramidal aperture towards the sun, and a
whitened wall or white paper screens, but no lens. He discloses
as a great secret the use of a concave speculum in front of the
aperture, to collect the rays passing through it, when the images
will be seen reversed, but by prolonging them beyond the centre
they would be seen 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.

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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. Hc notes the con-
venience of the method for solar observations and its prcvious
use by some of the observers already mentioned, as well as its
advantagcs 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 camcra to cartography and the reproduction of drawings,
which is one of its principal uses at the present time. In
the Diversarum Speculationum Mathematicarum et Physicarum
(1585), by the Venetian Giovanni Battista Benedetti, there is a
letter in which he discusses the simple camera obscura and
mentions the improvement some one had made in it by the use
of a double convex lens in the aperture; he also says that the
images could be made erect by reflection from any plane mirror.

Thus the use of the camera and of the lens with it was well
known bcfore Porta published his second edition of the Magia
Naturalis in 1589. In this the description of the camera obscura
is in lib. xvii. cap. 6. The use of the convex lens, which is given
as a great secret, in place of the concave speculum of the first
edition, is not so clearly describcd as by Barbaro; the addition
of the Concave spcculum is proposcd for making the images
larger and clearcr, and also for making them erect, but no details
are given. He describes some entertaining peep-show arrange-
ments, possibly similar to Alberti's, and indicatcs how the dark
chamber with a concave speculum can be used for observing
eclipses. Thcre is no mcntion whatcver of a portable box or
construction bcyond the darkened room, nor is there in his later
work, De Refractione Optices Parte (1593), in which he discusses
the analogy bctween vision and the simple dark room with an
aperture, but incorrectly. Though Porta's merits were un-
doubtedly great, he did not invent or improve thc camera
obscura. His only novelty was the use of it as a peep-show;
his descriptions of it are vague, but being published in a book of
general reference, which bccamc popular, he acquircd credit for
the invention.

The first to take up the camera obscura after Porta was Kepler,
who used it in the old way for solar observations in 1600, and
in his Ad Vitellionem Paralipomena (1604) discusses the early
problems of the passages of light through small apertures, and
the rationale of the simple dark chamber[.] He was the first to
describe an instrumcnt fittcd with a sight and paper screen for
observing the diamcters of the sun and moon in a dark room.
In his later book, Dioptrice (1611), he fully discusses refraction
and the use of lenses, showing the action of the double convex
lens in the camcra obscura, with the principles which regulate
its use and the rcason of thc reversal of the image[.] He also
demonstrates how enlarged images can be produced and projected
on paper by using a concave lens at a suitable distance behind
the convcx, as in modern telephotographic lenses. He was the
first to use the term camera obscura, and in a letter from Sir H.
Wotton written to Lord Bacon in 1620 we learn that Kepler had
made himself a portable dark tent fitted with a telescope lens
and used for sketching landscapes. Further, he extended the
work of Maurolycus, and demonstrated the exact analogy
between the eye and the camera and the arrangement by which
an inverted image is produced on the retina.

ln 1609 the telescope came into use, and the danger of observ-
ing the sun with it was soon discovered. In 1611 Johann
Fabricius publishcd his observations of sun-spots and describes
how he and his father fell back upon the old mcthod of projecting
tbe sun's image in a darkened room, finding that they could
observe the spots just as well as with the telescope. They do
not seem to have used a lens, or thought of using the telescope
for projecting an enlarged image on Kepler's principle. This

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