542
vocation. During this period he met professor Alfred
Donné, whom he followed to the Medical school and
attended microscopy courses, before becoming a profes-
sor there himself. The two men remained very close. In
1845, Foucault succeeded Donné as the scientifi c writer
of the Journal des Débats.
Since 1839, Donné had an interest in the daguerreo-
type and its possible applications in the fi eld of medi-
cine. Undoubtedly under his infl uence, Foucault started
work on the technique and, according to his biographer
Cornu, “built an apparatus from his hands.” With Donné,
he attempted to take daguerreotypes of enlarged glob-
ules from 20 to 400 times actual size by using a solar
microscope-daguerreotype. Summarizing several years
of work, these images appeared in 1844 in l’Atlas du
cours de microscopie. The edition included 80 plates
based on daguerreotypes taken by Foucault, and were
published in 4 successive editions. The same year, the
two men presented their photoelectric microscope, used
by Donné at the time of its conferences.
In parallel, in collaboration with another doctor,
Doctor Belfi eld-Lefevre, Foucault undertook research
on the sensitive layers of the daguerrean image. In Au-
gust 1843, the two men spoke in front of the Academy
of Science of Paris on the preparation of the sensitive
layer that received the image, and again in October 1846
noting the process that made it possible to reproduce,
with equal perfection, the brilliant and obscure tones
of the model.
It is hard to determine with certainty the date of the
beginning of Foucault’s collaboration with Fizeau. In
1841, an echo of previous searches, Foucault developed
one slide with bromine allowing an application of uni-
form bromide. However, in April 1844, Foucault and
Fizeau agreed for the fi rst time to speak in front of the
Academy of Science (research on the intensity of car-
bon light). Until 1849, probably encouraged by Arago,
they jointly continued their experiments to analyze and
measure the light required and involved particularly
in the phenomenon of the interferences between two
rays of light and in the action of the solar spectrum on
sensitized surfaces. On August 2, 1845, they obtained
at the Observatory of Paris the fi rst daguerrienne image
of the Sun now known in Paris as CNAM.
Their research became more directed towards the
questions of pure physics in particular, relating to
the determination the speed of the light. In 1849, an
estrangement between the two men put an end to their
collaboration. This same year, Fizeau determined the
speed of light and Foucault determined the relative speed
of light in air and water. Soon after Foucault presented a
photoelectric apparatus to the Academy of Science, and
continued to be interested in various questions related
to optics as on the fi rst stereoscopic process.
His activity in the fi eld of photography slowed down;
however, Foucault continued his work in the fi eld of
physics. In 1851, he built his famous “pendulum”
making it possible to highlight gravity. The experiment
received the recognition of his peers and he became
an international celebrity, starting a true “pendular
fashion.”
Four years later he was appointed to a recently cre-
ated position at l’Observatoire de Paris, where he was
responsible for the study of the sun and the construction
of new instruments to observe it, and tried with little
luck to develop the ability to photograph it. In 1862,
he was named a regular member of the prestigious Bu-
reau of Longitudes and a foreign member of the Royal
Society, London from which he had received in 1855
the Copley medal. In 1865 fi nally, he was elected as a
member of the Academy of Science of Paris, (section
of mechanics), of Berlin. Every Thursday morning, his
scientifi c discussion would attract off the street of Assas
the national and international scientifi c celebrities who
would discuss scientifi c matters in his living room.
Even if his activity as a photographer seemed to
be fi nished, his interest in photography and questions
regarding optics remained. In 1854, he became part
of the founding members of the Société française de
photographie and became a member of its board of
directors. He remained in this position until his death
in 1868. In 1860, he was sent to Spain to photograph,
on behalf of the Observatory of Paris, the total solar
eclipse. Two years later, he developed a heliostat for
photographic enlargement, which was built by his son-
in-law, the Dubosq optician. Suffering since 1861 from
incurable and progressive paralysis, he died in Paris on
February 11, 1868.
His photographic production now known, consisting
of daguerreotypes of Paris and a still life of a bunch
of grapes, is extremely small, with the exception of
the scientific images concerned with the Sun and
microscopy. In the public collections today, this work
is mainly preserved at Paris, the Société française de
photographie, and the musée du Conservatoire national
des arts et Métiers.
Quentin BajacFurther Reading
J. Bertrand, Historical Praise of Leon Foucault, Paris, Firmin-
Didot, 1882.
Stephan Deligeorges, Foucault and his pendulums, Paris, 1990.
P.Gilbert, “Leon Foucault, his life and his oeuvre scientifi c,”
Review of the scientifi c questions, Brussels, 1879.
M. Lissajous, Historical Note on the life and work of Leon
Foucault.
Agnes Marillier, “An amateur with the Academy,” Books Science
and life, February 1995.