The letter c is the standard symbol for the speed of light, but that was not always the case. I describe how c was first introduced into the theory of electromagnetism and the stages by which it came to be used to denote the speed of light.

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Why is c the symbol for the speed of light?
,” http://math.ucr.edu/home/baez/physics/relativity/velocityoflight/c.html
16.

Other spelling changes between Weber’s original papers and reprints are from Elektricität to Elektrizität and from Maasse to Masse.

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10
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On physical lines of force
,”
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348
(
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);
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On physical lines of force
,”
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James Clerk
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On physical lines of force
,”
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Fizeau
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Sur un expérience relative à la vitesse de propagation de la lumière
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29
,
90
92
(
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).
English translation in
A Source Book in Physics
, edited by
William F.
Magie
(
McGraw-Hill
, New York,
1935
), pp.
340
342
.
31.
James Clerk
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,
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32.
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Theories of action at a distance
,” p.
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34.
Paul
Drude
,
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483
.
35.
Paul
Drude
,
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. This publication is a reprint of the 1902 edition.
36.
H. A.
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,
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89
92
. These pages are reprinted in Ref. 37, pp. 1–5 under the title “Der Interferenzversuch Michelsons.” English translation by W. Perrett and G. B. Jeffery in Ref. 38, pp. 3–7 “Michelson’s interference experiment.” The translation substitutes c for V to denote the speed of light.
37.
H. A.
Lorentz
 et al,
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(
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, Stuttgart,
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).
38.
H. A.
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, New York,
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39.
See, for example,
Albert A.
Michelson
, “
Experimental determination of the velocity of light
,”
Nature (London)
21
,
94
96
(
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);
Albert A.
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Experimental determination of the velocity of light
,”
Nature (London)
120–122
,
226
(
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).
Albert A.
Michelson
and
Edward W.
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, “
On the relative motion of the earth and the luminiferous ether
,”
Am. J. Sci.
34
,
333
345
(
1887
).
A. A.
Michelson
,
F. G.
Pease
, and
F.
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,”
Astrophys. J.
82
,
26
61
(
1935
).
Reprinted in
J. H.
Sanders
,
The Velocity of Light
(
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, Oxford,
1965
), pp.
43
79
.
40.
Henrich
Hertz
,
Electric Waves
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.
41.

Reference 35, p. 265.

42.
Oliver
Heaviside
,
Electromagnetic Theory
(
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), p.
79
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43.
Albert
Einstein
, “
Zur Elektrodynamik bewegter Körper
,”
Ann. Phys.
17
,
891
921
(
1905
). Reprinted in Ref. 46, Vol. 2, pp. 276–306. English translation in Ref. 47, Vol. 2, pp. 140–171, “On the electrodynamics of moving bodies.” The translation in Ref. 38 pp. 37–65, substitutes c for V to denote the speed of light.
44.
Albert
Einstein
, “
Ist die Trägheit eines Körpers von seinem Energiehalt abhängig?
,”
Ann. Phys.
18
,
639
641
(
1905
). Reprinted in Ref. 46, Vol. 2, pp. 312–314. English translation in Ref. 47, Vol. 2, pp. 172–174, “Does the inertia of a body depend upon its energy content?” The translation in Ref. 38 pp. 69–71, substitutes c for V to denote the speed of light.
45.
Albert
Einstein
, “
Über die von Relativitätsprinzip geforderte Trägheit der Energie
,”
Ann. Phys.
23
,
371
384
(
1907
). Reprinted in Ref. 46, Vol. 2, pp. 414–427, English translation in Ref. 47, Vol. 2, pp. 238–250, “On the inertia of energy required by the relativity principle.”
46.
The Collected Papers of Albert Einstein
, edited by
John
Stachel
(
Princeton University Press
, Princeton, NJ,
1989
).
47.
The Collected Papers of Albert Einstein: English Translation
, translated by Anna Beck (
Princeton University Press
, Princeton, NJ,
1989
).
48.
Albert
Einstein
, “
Über die Relativitätsprinzip und die aus demselben gezogenen Folgerungen
,”
Jahrbuch der Radioaktivität und Elektronik
4
,
411
462
(
1907
). Reprinted in Ref. 46, Vol. 2, pp. 433–484. English translation in Ref. 47, Vol. 2, pp. 252–310, “On the relativity principle and the conclusions drawn from it.”
49.
Max
Abraham
, “
Prinzipien der Dynamik des Electrons
,”
Ann. Phys.
10
,
105
179
(
1903
).
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