Pendulum plane of oscillation of a pendulum, like a gyroscope, tends to stay constant regardless of the motion of the pivot, and that this could be used to demonstrate the rotation of the Earth. He suspended a pendulum free to swing in two dimensions (later named the Foucault pendulum) from the dome of the Panthéon in Paris. The length of the cord was . Once the pendulum was set in motion, the plane of swing was observed to precess or rotate 360° clockwise in about 32 hours. This was the first demonstration of the Earth's rotation that didn't depend on celestial
In Which We Serve leads to a flashback in which Blake remembers how he met his wife-to-be, Freda, on a train while on leave. It is also revealed that she is related to the "Torrin"'s affable Chief Petty Officer Hardy (Miles). When both men return to sea, Freda moves in with CPO Hardy's wife and mother-in-law. The "Torrin" participates in the Dunkirk evacuation of the British Expeditionary Force, (portrayed in the film by the 5th Battalion of the Coldstream Guards). Meanwhile, the nightly Blitz takes its toll on British towns. Blake soon gets a letter from home to say that Freda has given birth