This Month in Physics, , APS News , July (2008). Princeton University, . W. Levin, MIT, , YouTube-video. V. Courtillot and J.-L. Le Mouël, , Reviews of Geophysics, , RG3008 (2007). C. Blondel and B. Wolff, CNRS, , tidlig historie om Ørsteds og Ampères eksperiment.