In America and Great Britain people are on the whole well acquainted with the picturesque circumstances surrounding the discovery of the ‘line of position’ by the Merchant Navy captain, Thomas Sumner. On the other hand, less has been written about the personality of Admiral Marcq de St. Hilaire, and about his work which led him to propose the comprehensive and exact method, now universal, which bears his name. My intention, therefore, is not to go back over the theory or the practice, nor even the value of this system of position finding by comparing points. It is just a question of making this brilliant naval officer better known, his upbringing, character, and the historic circumstances of the perfect achievement of which he is the immortal author.