Superconductivity and carbon nanotubes, are Type I, while almost all impure and compound superconductors are Type II. Conversely, a spinning superconductor generates a magnetic field, precisely aligned with the spin axis. The effect, the London moment, was put to good use in Gravity Probe B. This experiment measured the magnetic fields of four superconducting gyroscopes to determine their spin axes. This was critical to the experiment since it is one of the few ways to accurately determine the spin axis of an otherwise featureless sphere. Superconductivity was discovered on April 8, 1911 by Heike Kamerlingh Onnes, who was studying the resistance
Frans Michel Penning Derksen in 1921 and they had four children named Lourens, Hendricus, Paul, and Nellie. In 1924, Penning was hired as an experimental physicist at the Dutch section of the Phillips research department located in the Strijp district of Eindhoven. Gilles Holst, former assistant to Heike Kamerlingh Onnes, and head of the Philips Natuurkundig Laboratorium (NatLab), tasked Penning with continuing research on gas discharge phenomena to develop new lamps. Penning investigated breakdown energy potentials of low pressure inert gas discharges. In 1926, Penning observed that electrons under direct voltage current in low-pressure mercury discharges reach high velocities due to high-frequency oscillations