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
Jacob Clay Jacob Clay Jacob Clay () (1882–1955) was a prominent Dutch physicist who first suggested and provided evidence that cosmic rays are charged particles. Clay was born "Jacob Claij" in Berkhout on 18 January 1882 as the son of Pieter Claij and Neeltje Molenaar. After attending the Erasmiaans Gymnasium, he studied physics at the University of Leiden under Heike Kamerlingh Onnes and Hendrik Antoon Lorentz. After obtaining his Ph.D. degree in 1908 he married Tettje Clay-Jolles with whom he had a son. After teaching in Leiden and at the Technische Hogeschool in Delft from 1906 to 1920, he was appointed Professor