John Clerk (10 December 1728 – 10 May 1812), sometimes known as 'Clerk of Eldin', was a prominent figure in the Scottish Enlightenment. He was the sixth son of Sir John Clerk of Penicuik (1676 - 1755) a politician and advocate who had been created a hereditary baronet in 1679, and who became a prominent patron of the arts, including to the artist Allan Ramsay (1713-84) and the architect William Adam (1689 - 1748).. His mother was Janet Inglis, daughter of Sir John Inglis of Cramond.
John Clerk enrolled at Edinburgh University to study medicine, but abandoned his studies and entered into business. He made his fortune as a merchant and manager of a coal mine, and bought the property of Eldin near Edinburgh. There, he devoted himself to science and art, and became a close friend of the geologist James Hutton, the philosopher David Hume, the mathematician John Playfair (1748 - 1819) and other leading members of the Scottish Enlightenment, and also became an expert on naval tactics. In his Essay on Naval Tactics (1779, published 1790), Clerk proposed the tactic of "cutting the line" (sailing into the enemy's line of ships and attacking the rear with the whole force of the attacking fleet). Admiral Horatio Nelson used Clerk's work in the Battle of Trafalgar in 1805, to win the most significant naval battle of the Napoleonic wars.
In the preface to the second edition of his "Essay on Naval Tactics," 1804. he wrote: "I had acquired a strong passion for nautical affairs when a mere child. At ten years old, before I had seen a ship, or even the sea at a less distance than four or five miles, I formed an acquaintance at school with some boys who had come from a distant sea-port, who instructed me in the different parts of a ship from a model which they had procured. I had afterwards frequent opportunities of seeing and examining ships at the neighbouring port of Leith, which increased my passion for the subject; and I was soon in possession of a number of models, many of them of my own construction, which I used to sail on a piece of water in my father’s pleasure grounds, where there was also a boat with sails, which furnished me with much employment. I had studied Robinson Crusoe, and I read all the sea voyages I could procure."