521521
FARADAY, MICHAEL
piece of reverse engineering was the key to reproducing
Fraunhofer’s success. But their attempts to use these
formulae repeatedly failed. It became evident that the
conditions of manufacture, including the materials and
shape of the melting pots, the temperature progression
of the furnace, and the stirring techniques and materials
were also important.
In 1825 a subcommittee of Dolland, Herschel, and
Faraday was set up to closely supervise the glassmakers.
In 1827 it was deemed necessary to move the furnace
operations to the Royal Institution so that Faraday
could supervise them directly. The results continued to
be imperfect, yielding glass with bubbles and striae. It
became clearer that the stirring technique was crucial
to getting uniformity in the glass, but this goal eluded
Faraday. The few successes Faraday achieved were not
reproducible. In May 1830 he resigned the Commit-
tee. Fraunhofer had meanwhile died in 1826, and his
secrets, known to former associates as well as some of
his coworkers, were carried abroad. They were put to
use in Switzerland and then in France. The expertise
eventually found its way back to England that led to a
revival of British optics.
In the 1820s Faraday noticed, while experimenting
with a manganese-doped glass of purple color, that the
glass turned darker if exposed to sunlight. It could turn
lighter again if removed from the light. This must be one
of the earliest descriptions of photochromic behavior,
and is directly related to photography. He never tried to
produce an image with this material, though he could
have. A silver halide-doped glass with the same ability
found practical application in darkening/clearing sun-
glasses in the late 20th century.
As mentioned above Faraday was a close associate
and became a friend of Sir John Herschel, and likely
through him got to know Henry Talbot. In 1839 when
Talbot wished to describe his work on photographic im-
ages Faraday provided the fi rst public announcement of
his photogenic drawing process on the 25th of January
before the Royal Institution. He gave the fi rst talk on the
details of the process (see the Literary Gazette of Feb.
2, 1839). Faraday supported Talbot in his admission to
the Royal Society, but later opposed the granting to him
of a baronetcy. Faraday connected to many others in the
circle of early photographers and sat for a number of
portraits, including one by Mayall.
Faraday had always thought that symmetry of action
in physical phenomena was important and should apply
to electricity and magnetism. He had demonstrated in
1821 the electric motor principle, as outlined above.
He thought at the time that the reverse should work
and that there should be a way for a changing magnetic
force to cause an electric current to fl ow in a conduc-
tor. In 1831 he resumed his electrical experiments. He
demonstrated that rotating a coil of wire between the
poles of one or more magnets would induce an elec-
tric current to fl ow in the coil. This is the basis of the
electric generator. With this discovery the modern age
of electricity began.
In the 1840s and 50s Faraday taught chemistry and
continued his electrical and optical researches. He dis-
covered that magnetic fi elds could affect the properties
of light both as it traveled in the vacuum and through
matter. He demonstrated that strong magnetic fi elds
could rotate the plane of polarization of polarized light
as it traveled through glass placed between the poles of
a large magnet (Faraday rotation”). This clearly hinted,
based on the earlier discovery of the link between
electricity and magnetism that light’s nature was both
electrical and magnetic.
In pondering the fact that electric charge and magnets
could exert forces on things the charge and magnets do
not touch (as is the case for matter and gravitational
attraction), Faraday dropped the old term of action-
at-a-distance, and began to speak of this infl uence as
evidence for electric and magnetic “fi elds,” existing in
and infl uencing the properties of space. The magnetic
fi eld could easily be visualized by sprinkling iron fi lings
on a sheet of paper under which was placed a magnet.
This now common experiment, and a similar one that
can map electric force, made it easy to speak of fi eld
lines or lines of force, with their own reality, more or
less independent of their sources in electric charges and
magnetic poles.
The magneto-optical phenomena demonstrated by
Faraday and the fi eld idea were picked up, elaborated
and mathematized by Maxwell in the 1850s and 1860s
into a self-consistent set of equations which described
static electric charge, currents in the vacuum and in
conductors, and the consequent electromagnetic fi elds
generated by the latter sources. He showed that electric
and magnetic fi elds could propagate each other as waves
and derived the waves’ speed of propagation from the
known electrical properties of conductors and the vac-
uum, and showed that this speed was in agreement with
the previous best measurements of the speed of light.
This established the electromagnetic wave nature of light
and allowed Maxwell to predict the existence of radio
waves and the rest of the electromagnetic spectrum. This
foundation to the electromagnetic wave theory of light
is Faraday’s single greatest contribution to traditional
photography and the newer digital photography.
Faraday did experiments until 1855 and lectured
until 1861. His health declined during that time and he
died in 1867.
William R. AlschulerSee also: Maxwell, James Clerk; Davy, Sir Humphry;
Young, Thomas; and Herschel, Sir John Frederick
William.