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In trying to find the origin of the term electromotive force I came across this material in a history of science book in my collection. "Science, The Never-Ending Quest", by William Vergara, 1965, pages 296,297 "Ohm noticed almost immediately that if a number of voltaic cells are connected in series ... the current increases as additional cells are added. The current is then proportional to the number of cells in the battery. Here was a clear connection, at last, between the tension of a battery and the current it can produce. ... His analogy was the flow of heat along a metal wire or rod. ...The similarity between the flow of heat and the flow of electric current suggested the introduction of a quantity whose behavior in electrical circuits was similar to that of temperature in the theory of heat. That quantity was the tension of a voltaic cell .... Ohm called it the electroscopic force of a cell, and it is now called an electromotive force. ... Ohm published his conclusions in a book and in a series
I did a quick search through my collection of old physics books. The relevant results are listed below. The title, author, printing date and page references are listed for each book. The potential difference is referred to as "intensity or tension" in sources 1,2,3,4. The earliest reference I found to the term "electromotive force" is in a book printed in 1881. Sources 5 - 8 give examples of the use of the term. Source 9 speculates on the origin of the term.
The Natural Philosophy books I have that were printed before 1840 generally have less specific statements about potential difference and much less discussion on electricity that the books printed after 1840.
I also did some searching at goggle that led to these web sites:
http://www.electricityforum.com/electricity-history.html
This web site credits Kirchoff with deducing that Ohm's electroscopic force and electrostatic potential are identical.
http://www.sizes.com/units/volt.htm
"The cgs <http://www.sizes.com/units/sys_cgs.htm> unit of electromotive force (e.m.f.) was based on an idea of F. E. Neumann in 1825. One cgs unit of e.m.f. was produced in any electric circuit cutting one magnetic line of force per second. " (See the following site for clarification on the date...Greg Clements)
http://www.sp.phy.cam.ac.uk/teaching/em/inductn.pdf
This site gives 1845 as the date for Neumann's conclusion. Since Faraday discovered electromagnetic induction in 1831 I think the 1845 date is probably correct.
Greg Clements
Midland Lutheran College
clements@mlc.edu
1. "A Compendium of Natural Philosophy" by Denison Olmsted, 1848, page 217 "The term electricity is used to denote both the unknown cause of electrical phenomena, and the science which treats of electrical phenomena and their causes."
page 241 "The object of the battery is to accumulate a great quantity of the electric fluid, which is in proportion to the extent of surface; the intensity, or elastic force, as indicated by the quadrant electrometer, is no greater in the battery when charged, than in a single charged jar."
The book does not use the term electromotive force.
2. "The Science of Common Things; A Familiar Explanation of the First Principles of Physical Science" by David Wells, 1857, page 292 "The electricity developed by the action of a single pair of plates immersed in acid water is very feeble: how can it be increased? By increasing the number of the plates and the quantity of the liquid, we increase the intensity of the electricity developed." This book does not use the term electromotive force.
3. "An Introduction to Natural Philosophy" by Denison Olmsted, Revised by E.S. Snell 1869, page 369 "The great difference between the galvanic and the frictional electricity is, that the latter is in a state of great intensity, or tension, as it is often called, darting violently, and with the evolution of sound and light, through an obstructing substance, while the former has very low tension, flowing in a comparatively gentle stream through conductors, and unable to pass across interruptions, unless they are exceedingly small." This book does not use the term electromotive force.
4. "Fourteen Weeks in Physics" by J. Dorman Steele, 1879, page 233 "Electrical Potential is a property of a body by which electricity tends to go from it to another, and is measured by the resistance met in the passage. This term is to electricity what temperature is to heat."
page 235 "A battery may develop a great quantity of electricity having a low degree of intensity, or a small quantity having a high intensity. .. The intensity of the electric force depends on the number of cells; the quantity, on their size." This book does not use the term electromotive force.
5. "Elements of Natural Philosophy, A Text-Book for High Schools and Academies" by Elroy Avery, 1881, page 239 "Experiments show that the quantity of electricity passing in a unit of time, over a given conductor, is directly proportional to the electromotive force. (This electromotive force, 'E.M.F.,' is the supposed force that causes or tends to cause a transfer of electricity from one point to another.)"
6. "School Physics" by Elroy Avery, 1895, page 424 "Whenever a positive charge is placed upon a conductor, it raises the potential at the point of application, and there is a flow of electrification until the surface of the conductor is an equipotential surface. If two conductors at different potentials are connected by a wire, a transfer of electrification will take place until the difference of potential disappears. Whatever its nature, the agency that tends to produce such a transfer is called electromotive force.
page 443 "As hydraulic pressure might be called water-moving force, so electrical pressure is called electromotive force (E.M.F.) The unit of electrical pressure is called the volt, and is almost the same as the electromotive force of a cell consisting of a copper and a zinc plate immersed in a solution of zinc sulphate."
(By the way, this book does not mention the electron.)
7. "Elements of Physics" by George Hoadley, 1908, page 312 "The difference of potential at the terminals of a cell when it is on open circuit is its electro-motive force, or E.M.F."
8. "A First Course in Physics" by Robert Millikan and Henry Gale, 1913, page 247 "The potential difference which a galvanic cell or any other generator of electricity is able to maintain between its terminals when these terminals are not connected by a wire, that is, the total electrical pressure which the generator is capable of exerting, is commonly called its electromotive force, usually abbreviated to E.M.F. The E.M.F. of an electrical generator may then be defined as its capacity for producing electrical pressure, or P.D.
9. "Physics A Textbook For Colleges" by Oscar Stewart, 1931, page 453 "Electromotive force has a misleading name, for it is not a force but a work factor; when multiplied by quantity, it gives work. ... The name had its origin in the analogy of an electric current to the flow of a liquid."
----- Original Message -----
From: Ludwik Kowalski <mailto:kowalskil@MAIL.MONTCLAIR.EDU> To: PHYS-L@LISTS.NAU.EDU
Sent: Monday, February 28, 2005 9:57 AM
Subject: Re: A battery cell
1) It would be useful if somebody with an easy access to very old
physics texts could trace the history of the term "electromotive
force," and share the result with the rest us. For the time being let
me speculate.