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
Helium by Dutch physicist Heike Kamerlingh Onnes by cooling the gas to less than one kelvin. He tried to solidify it by further reducing the temperature but failed because helium does not solidify at atmospheric pressure. Onnes' student Willem Hendrik Keesom was eventually able to solidify 1 cm of helium in 1926 by applying additional external pressure. In 1913, Niels Bohr published his "trilogy" on atomic structure that included a reconsideration of the Pickering–Fowler series as central evidence in support of his model of the atom. This series is named for Edward Charles Pickering, who in 1896 published observations of previously