HF The History of Photography 600pág

The history of the camera obscura 29
that Bruce and Balugani drew with these two instruments at the same time and
within talking distance of each other.
Edward Dodwell relates in his Classical and Topographical Tour through Gm·tc 50 an
amusing experience he had while sketching with the camera obscura on the Acropolis
in 1805. The Turkish governor (Disdar) constantly put difficulties in Dodwell's way,
which could only be overcome by 'gifts' until one day he got rid of this mercenary
Turk in a most extraordinary manner. When Dodwell tried to explain the camera
obscura
The Disdar no sooner saw the temple instantaneously reflected on the paper in
all its lines and colours, than he imagined that I had produced the effect by some
magical process; his astonishment appeared mingled with alarm . . . . He again
looked into the camera obscura. At that moment, some of his soldiers happening
to pass before the reflecting glass, were beheld by the astonished Disdar walking
upon the paper: he now became outrageous, and after calling me pig, devil and
Buonaparte he told me that if I chose I might take away the temple and all the
stones in the Citadel, but that he would never permit me to conjure his soldiers
into my box. When I found that it was in vain to reason with his ignorance, I
changed my tone, and told him that if he did not leave me unmolested, I would
put him into my box, and that he should find it a very difficult matter to get out
agam.
Visibly alarmed, the Disdar immediately retired discomfited, and henceforth carefully
avoided Dodwell and his dangerous box.
Before leaving this chapter we should mention an important improvement respecting
the optics of the camera obscura. The English optician JOHN DOLLOND in 1758
made public57 a new lens system by means of which chromatic aberration was
avoided. A similar invention had actually been made, though not published, by
Chester Moor Hall in 1733. Both his and Dollond's improvements were designed
for the telescope. Zacharias Traber, Rector of the Jesuit College in Vienna, in his
Nervus Opticus (1675), credits the Neapolitan Eustachio Divinus with the invention
of an achromatic telescope. This had nineteen convex lenses enclosed in a tube 19
cubits long, and being made of very fine glass, prevented the discoloration of the
image. Dollond combined two lenses of different dispersive powers, i.e. one of flint
glass and one of crown glass, and such achromatic lenses have been employed in
good optical instruments ever since.
WILLIAM HYDE WOLLASTON ' s camera lucida, introduced in 1807,58 is not a camera Pl 14
at all-as is often mistakenly assumed, perhaps because Fox Talbot at one time drew
with its aid-but a small optical instrument for drawing in broad daylight. By means
of a prism, the artist saw a virtual image on his paper which facilitated the delineation
of the object or view, but the image was not visible to anyone but the user of the
instrument. It will be evident that there is no connection between this instrument
and Dr Hooke's camera lucida already referred to ; and in Wollaston's the name
'camera' was certainly misapplied.