The possibility of seiemic measurement of the rotation of the Earth's core

The calculations of Inglis show that the rate of transfer of angular momentum to the Earth's (liquid) core may be small enough to permit the axis of rotation of the core to lag about 2° behind that of the rock‐mantle in the precessional motion of the Earth. The travel‐time of P′ would be altered by about one‐fifth of a second, which is too small to be detected by a single observation made with even the best instrument, but can be brought out statistically when we have accumulated about three thousand clear measurements, on sensitive vertical‐component seismographs, of the P′‐waves from accurately located earthquakes.