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tion, the radiometer. He received a number of honorary
university degrees and distinctions in recognition of
his outstanding scientifi c work, including a knighthood
in 1897 and the Order of Merit in 1910. Widowed in
1916, Crookes died on 4 April 1919 at the age of 87 in
Kensington Park Gardens.
See Also: Great Exhibition of the Works of Industry
of All Nations, Crystal Palace, Hyde Park (1851);
Photographic News (1858–1908); and Spirit, Ghost,
and Psychic Photography.
Further Reading
Barrett, William, [Sir William Crookes Testimonial], Proceedings
of the Society for Psychical Research, 31 (1921), 12–29.
Crookes, William, Crookes and the Spirit World, edited by R.
George Medhurst, New York: Taplinger, 1972.
D’Albe, E. E. Fournier, The Life of Sir William Crookes, New
York: D. Appleton, 1924.
Hall, Trevor H., Florence Cook and William Crookes: A Footnote
to an Enquiry, London: Tomorrow Books, 1963.
Hall, Trevor H., The Medium and the Scientist, Buffalo, New
York: Prometheus Books, 1984.
Medhurst, R., George and K. M. Goldney, “William Crookes and
the Physical Phenomena of Mediumship,” Proceedings of the
Society for Psychical Research 54, Part 195, March 1964.
Palfreman, John, “William Crookes: Spiritualism and Science,”
Ethics in Science and Medicine 3, 1976, 211–27.
Stein, Gordon, The Sorcerer of Kings: The Case of Daniel
Donglas Home and William Crookes, Buffalo, New York:
Prometheus Books, 1993.
CROS, CHARLES EMILE HORTENSIUS
(1842–1888)
French physician and poet
Cros, a poet, was born in 1842. In photography, he is
known for his early three-color photographic experi-
ments. Cros had, like Ducos du Hauron, been working
on a subtractive method to obtain full color prints. Cros
did not have a studio of his own, instead he performed
his photographic experiments in his friend’s, Herzogs
von Chaulness, photographic studio.
Cros made photographs through red, green and blue
fi lters, which were converted to positives. However,
rather than converting them into transparencies for pro-
jection he dyed each positive with the complementary
color of its original fi lter. Precisely overlapped on white
paper, the three sheets fused into a full color image of
the original. Unfortunately, the color sensitivity of b/w
negative emulsions at this time was rather poor. The fi lm
was mainly sensitive to blue and some parts of the green
spectrum. There was virtually no red sensitivity at all.
Therefore Cros’ color prints were less than perfect. In
a letter, sent to the Academy of Sciences in Paris, Cros
described his color photography experiments. The let-
ter was deposit on December 2, 1867 not to be opened
until 1876.
Only two days after Ducos du Hauron was granted a
patent on the same technique, Cros published the correct
principle of the subtractive color method in Les Mondes,
February 25, 1869.
Cros described a photochromoscope and how to set
up the components within the camera to make three-
color separated negatives. Later, on May 7, 1869, did
Cros present his technique at the Société française de
photographie. On the same day had Alphonse Davanne,
the vice-president of the society read a report about
Ducos du Hauron’s similar work.
On 23 December 1878 a seminar by Cros was pre-
sented at the Academy of Sciences in Paris in which he
described a photochromoscope which he referred to as
a Chromometre.
Cros invented the hydrotype process in 1881, which
is a reversed collotype process. It can be used in color
printing. A gelatin image is made to absorb dyes in
proportion to the action of light so that, when a paper
is brought in contact with the stained plate, a color im-
age can be transferred from the dye. The color image
recorded in a camera is received on a chromo-sensitive
surface composed of red, yellow and blue superim-
posed or juxtaposed, the color-sensitive material being
so selected that each pigment is destroyed by light of
complimentary color. Thus, the orange rays destroy the
blue pigment, the green rays destroy the red pigment,
and the violet rays destroy the yellow pigment. The glass
plates were made by having collodion colored red by
cartharnine, then gelatin colored blue by phyllocyanide,
and fi nally collodion made yellow by curcuma.
Hans I. BjelkhagenBiography
Charles Emile Hortensius Cros was born on October 1,
1842, in Fabrezan, France (Department of Aude) After
his baccalaureate in 1859 Cros started to study medicine
which he never completed. Instead, he started to live a
bohemian life, meeting with artist and writing poems.
Cros has published many poems, e.g., Le coffret de
santal, for which he was awarded the Juglar Prize.
On December 2, 1867, Cros was granted a patent on
his three-color helichromy method.
His book Solution générale du problème de la Pho-
tographie des couleurs was published in 1869. In April
1877 Cros described a device to record and replay acoustic
waves. Instead of storing the sound on cylinders as was
chosen by Edison, Cros suggested the used of a disc
instead.
Cros married Mary Hjardemal in 1878 and they had
two sons, Guy-Charles (1879–1956) and René (1880–
1898). Cros died on August 9, 1888, in Paris.