Plot: Dan Snow examines the growth of Britain's empire in the late 18th century, when the Navy's relationship with the pre-eminent scientific institution, the Royal Society, led to the exploration of the Pacific and the discovery of Australia. But with the threat of an attack by a resurgent France imminent, Whitehall was forced to introduce income tax to improve the ships, and in a conflict that resulted in the death of Admiral Nelson, the country's fleet defeated the French and Spanish at the Battle of Trafalgar in 1805