1911 Encyclopædia Britannica/Ohm, Georg Simon

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OHM, GEORG SIMON (1787-1854), German physicist, was born at Erlangen on the 16th of March 1787, and was educated at the university there. He became professor of mathematics in the Jesuits' college at Cologne in 1817 and in the polytechnic school of Nuremberg in 1833, and in 1852 professor of experimental physics in the university of Munich, where he died on the 17th of July 1854. His writings were numerous, but, with one important exception, not of the first order. The exception is his pamphlet published in Berlin in 1827, with the title Die galvanische Kette mathematisch bearbeitet. This work, the germs of which had appeared in the two preceding years in the journals of Schweigger and Poggendorff, has exerted most important influence on the whole development of the theory and applications of current electricity, and Ohm's name has been incorporated in the terminology of electrical science. Nowadays "Ohm's Law," as it is called, in which all that is most valuable in the pamphlet is summarized, is as universally known as anything in physics. The equation for the propagation of electricity formed on Ohm's principles is identical with that of J. B. J. Fourier for the propagation of heat; and if, in Fourier's solution of any problem of heat-conduction, we change the word "temperature" to "potential" and write "electric current" instead of "flux of heat," we have the solution of a corresponding problem of electric conduction. The basis of Fourier's work was his clear conception and definition of conductivity. But this involves an assumption, undoubtedly true for small temperature-gradients, but still an assumption, viz. that, all else being the same, the flux of heat is strictly proportional to the gradient of temperature. An exactly similar assumption is made in the statement of Ohm's law, i.e. that, other things being alike, the strength of the current is at each point proportional to the gradient of potential. It happens, however, that with our modern methods it is much more easy to test the accuracy of the assumption in the case of electricity than in that of heat; and it has accordingly been shown by J. Clerk Maxwell and George Chrystal that Ohm's law is true, within the limits of experimental error, even when the currents are so powerful as almost to fuse the conducting wire.