The year 1971 marked the first centenary of the publication of a paper on navigation which appeared in the Proceedings of the Royal Society of London in which the author, Sir William Thomson (later Lord Kelvin) described a new method of determining an astronomical position line. The method was impracticable and was not, therefore, adopted by practical seamen. Nevertheless, its design is ingenious and interesting, and an investigation of its principles adds lustre to the genius of its inventor—reputedly one of the most eminent philosophers of the nineteenth century. Although the method failed in the eyes of the mariners for whom it was intended, Thomson sparked off an interest in short-method tables which has persisted even to the present day.