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
Johannes Diderik van der Waals the van der Waals equation of state can be expressed as a simple function of the critical pressure, critical volume, and critical temperature. This general form is applicable to all substances (see van der Waals equation.) The compound-specific constants "a" and "b" in the original equation are replaced by universal (compound-independent) quantities. It was this law which served as a guide during experiments which ultimately led to the liquefaction of hydrogen by James Dewar in 1898 and of helium by Heike Kamerlingh Onnes in 1908. In 1890, van der Waals published a treatise on the "Theory of Binary Solutions" in