  Universal conductance fluctuations are usually observed in the form of
aperiodic oscillations in the magnetoresistance of thin wires as a function of
the magnetic field B. If such oscillations are completely random at scales
exceeding \xi_B, their Fourier analysis should reveal a white noise spectrum at
frequencies below \xi_B^{-1}. Comparison with the results for 1D systems
suggests another scenario: according to it, such oscillations are due to the
superposition of incommensurate harmonics and their spectrum should contain
discrete frequencies. An accurate Fourier analysis of the classical experiment
by Washburn and Webb reveals a purely discrete spectrum in agreement with the
latter scenario. However, this spectrum is close in shape to the discrete white
noise spectrum whose properties are similar to a continuous one.
