Pendulum the pendulum could be used to measure the force of gravity. During his expedition to Cayenne, French Guiana in 1671, Jean Richer found that a pendulum clock was minutes per day slower at Cayenne than at Paris. From this he deduced that the force of gravity was lower at Cayenne. In 1687, Isaac Newton in "Principia Mathematica" showed that this was because the Earth was not a true sphere but slightly oblate (flattened at the poles) from the effect of centrifugal force due to its rotation, causing gravity to increase with latitude. Portable pendulums began to be taken on voyages
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