- Line of force
A line of force in Faraday's extended sense is synonymous with Maxwell's line of induction. [ 1907 Encyclopedia Britannica, [http://books.google.com/books?id=PAgEAAAAYAAJ&pg=PA64&dq=%22Line+of+force%22&as_brr=3 page 64] ] According to
J.J. Thomson, Faraday usually discusses "lines of force" as chains of polarized particles in a dielectric, yet sometimes Faraday discusses them as having an existence all their own as in stretching across a vacuum. [http://books.google.com/books?id=nGwOAAAAIAAJ&printsec=frontcover&dq=Notes+on+Recent+Researches+in+Electricity&as_brr=3#PPA2,M1 Notes on Recent Researches in Electricity and Magnetism] , Joseph John Thomson, James Clerk Maxwell, 1883 ] In addition to lines of force, J.J. Thomson--similar to Maxwell--also calls them tubes of electrostatic induction, or simply Faraday tubes. From the 20th century perspective, lines of force are energy linkages embedded in a 19th century unified field theory that led to more mathematically and experimentally sophisticated concepts and theories, including Maxwell's equations, electromagnetic waves, and Einstein's relativity.
Historical origin & differences in field theories
Lines of force originated with Michael Faraday, whose theory holds that all of reality is made up of force "itself". His theory predicts that electricity, light, and gravity have finite propagation delays. The theories and experimental data of later scientific figures such as Maxwell, Hertz, Einstein, and others are in agreement with the ramifications of Faraday's theory. Nevertheless, Faraday's theory remains distinct. Unlike Faraday, Maxwell and others (e.g., J.J. Thomson) thought that light and electricity must propagate through an ether. In Einstein's relativity, there is no ether, yet the physical reality of force is much weaker than in the theories of Faraday.
Fields of Force, William Berkson, 1974 ] Forces and Fields, Mary B. Hesse, 1961 ]
Views of Faraday
At first Faraday considered the physical reality of the "lines of force" as a possibility, yet several scholars agree that for Faraday their physical reality became a conviction. One scholar dates this change in the year 1838. "The Origins of Field Theory", L. Pearce Williams (Cornell University), 1966, Random House, p. 88 (a) , p.124 (b) ] Another scholar dates this final strengthening of his belief in 1852. [ "Energy, Force, and Matter", P.M. Harman, 1982, Cambridge University Press, p. 80 ] Faraday experimentally studied lines of magnetic force and lines of electrostatic force, showing them not to fit action at a distance models. In 1852 Faraday wrote On the physical character of the lines of magnetic force, examining gravity, radiation, and electricity and their possible relationships with the transmission medium, transmission propagation, and the receiving entity.
Views of Maxwell
Initially, Maxwell took an agnostic approach in his mathematization of Faraday's theories. This is seen in Maxwell's 1855 and 1856 papers: "On Faraday's Lines of Force" and "On Faraday's Electrotontic State".
Tube of force
Maxwell changed Faraday's phrase of lines of force to tubes of force, when expressing his fluidic assumptions involved in his mathematization of Faraday's theories. A tube of force, also called a tube of electrostatic induction or field tube, are the "lines of electric force" which moves so that its beginning traces a closed curve on a positive surface, its end will trace a corresponding closed curve on the negative surface, and the line of force itself will generate an inductive tubular surface. Such a tube is called a "
Solenoid". There is a pressure at right angles to a tube of force of one half the product of the dielectric and magnetic density. If through the growth of a field the tubes of force are spread sideways or in width there is a magnetic reaction to that growth in intensity of electric current. However, if a tube of force is caused to move endwise there is little or no drag to limit velocity. Tubes of force are absorbed by bodies imparting momentum and gravitational mass.
Early on in his research (circa 1831), Faraday calls the patterns of apparently continuous curves traced out in metalic filings near a magnet "magnetic curves". Later on he refers to them as just an instance of magnetic lines of force or simply lines of force. [ Faraday's Experimental Researches in Electricity: THe FIrst Series, Howard J. Fisher, 2004, Green Lion Press, p. 22 et. al ]
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