Number 21 (Story #1), February 13, 1991 by Phillip F. Schewe and Ben Stein THE QUANTUM HALL RESISTANCE IS THE SAME in gallium arsenide and silicon to within an uncertainty of 3.5 x 10-10. In 1980 Klaus von Klitzing discovered that under conditions of low temperature and high magnetic field, the Hall resistance for an electric current flowing in a semiconductor surface layer did not rise linearly with increasing magnetic field (as in the classic Hall effect observed since the 19th century) but instead exhibited plateaus in which the Hall resistance was equal to a fractional number times the ratio h/e2, where h is Planck's constant and e is the charge of the electron. This quantization of the Hall resistance has proved to be so precise that it became, as of January 1, 1990, the primary standard of resistance. Now scientists at the National Physical Laboratory and the University of Nottingham in Great Britain have compared directly (using a sensitive cryogenic comparator bridge) the Hall resistance in a GaAs/AlGaAs heterojunction with that in a silicon field effect transistor and found them to be the same to a new level of precision. Equivalently, the scientists claim that they have measured the von Klitzing constant, presumably equal to h/e2, with "a substantially lower uncertainty than that claimed for any previous measurement." This strengthens further the notion that the quantum Hall effect is independent of the host material. (A. Hartland et al., 25 Feb. 1991 issue of Physical Review Letters.)