It was then essential for the calculation of
longitude that a ship's
marine chronometer be accurate, but the astronomical calculations to ensure accuracy were such that could only conveniently be made in observatories. In 1818 Wauchope became interested in developing a method of signalling from an observatory to ships the exact time so that the chronometers on board could be rated. He advised the
Admiralty of his
Plan for ascertaining the rates of chronometers by signal, which described his "
time ball", a large hollow metal sphere rigged on a pole and attached to a mechanism so that it might be dropped at an exact time each day. In 1829 a test was made of his device at
Portsmouth on the south coast of England, where the
Royal Naval Academy was situated. In 1833 time balls were constructed at
Greenwich, and in 1836 at Liverpool and Edinburgh. Wauchope submitted his scheme to American and French ambassadors when they visited England. The
US Naval Observatory was established in Washington, D.C. and the first American time ball went into service in 1845. In 1834 his brother-in-law, Admiral
Patrick Campbell, invited him to be his flag captain. Wauchope accepted on the condition that no
prostitutes were to be allowed on board the ship. His insistence on this resulted in him being summoned before Sir
Thomas Hardy the
First Sea Lord, who ordered him to resign his commission. Wauchope told Sir Thomas: "It is written that whoremongers shall not enter heaven" (ibid, 103), and appealed to
Sir James Graham, the
First Lord of the Admiralty. He was allowed to take command of HMS
Thalia in June 1834 and was again stationed at the Cape where he became an intimate friend of Sir
John Herschel. In 1836-7 he patrolled off
West Africa to intercept slavers. His active naval career ended on his return to England in 1838. == Retirement ==