"Einstein's Gyros"
Longtime EPP Editor, József Illy's most recent publication "Einstein's Gyros", can be found in Physics in Perspective. Here's the introduction:
In 1992, W. Schröder and H. J. Treder called attention to Albert Einstein's short but fascinating detour into geophysics. (1) At the time, they were able to rely only on published papers—in the case of Einstein, on a footnote in his paper on the ether.
Since that time, Einstein's correspondence of the period has been published and we can draw a more detailed picture of why he embarked on a field so seemingly distant from his main interests. In October 1921, two engineers of the gyrocompass factory of Hermann Anschütz-Kaempfe in Kiel, Germany, launched a series of experiments. They rotated a brass cylinder around its axis, heated it by hot oil, and wondered whether a magnetic field arose around it. (2) It seemed to be a routine test, for there were several gyroscopes rotating in each gyrocompass the firm manufactured and if a magnetic field were to be produced by their mere rotation, it would seriously influence their operation.
Their reason for pursuing these experiments, however, was different: "Even though I cannot yet imagine clearly that a positive effect is to be expected, it is still for me the only reasonable possibility to bring the heat current together with the earth currents, since the latter can only be caused by an irreversible process." These lines were written in December by Albert Einstein, who had persuaded the engineers to perform the experiment. (3) Heat currents? Earth currents?
In a letter written to Hermann Anschütz-Kaempfe, the owner of the factory, Einstein called the possible positive result "of enormous interest." (4) Did he mean this with regard to the development of the gyrocompass? No. When, in June 1922, after several failed attempts, the engineers had given up, Einstein remarked, "I thank you very much for repeating the heat-rotation experiment. In thinking about the nature of the Earth's field, I have got bogged down in improbabilities." (5) By "field," he meant the magnetic field of the earth. Thus, the goal of the experiment was to check on a laboratory scale whether the sources of the geomagnetic field are the electric currents circulating in the earth that are sustained by its internal heat. However, before continuing, let us see how Einstein found himself at a gyrocompass factory.