for the next 13 years, which he characterised as "by far the most useful and therefore by far the happiest and most honorable period [of his life]". Smith published The Theory of Moral Sentiments in 1759, embodying some of his Glasgow lectures. This work was concerned with how human morality depends on sympathy between agent and spectator, or the individual and other members of society. Smith defined "mutual sympathy" as the basis of moral sentiments. He based his explanation, not on a special "moral sense" as the Third Lord Shaftesbury and Hutcheson had done, nor on utility as Hume did, but on mutual sympathy, a term best captured in modern parlance by the 20th-century concept of empathy, the capacity to recognise feelings that are being experienced by another being. Following the publication of The Theory of Moral Sentiments, Smith became so popular that many wealthy students left their schools in other countries to enroll at Glasgow to learn under Smith. At this time, Smith began to give more attention to jurisprudence and economics in his lectures and less to his theories of morals. For example, Smith lectured that the cause of increase in national wealth is labour, rather than the nation's quantity of gold or silver, which is the basis for mercantilism, the economic theory that dominated Western European economic policies at the time. In 1762, the University of Glasgow conferred on Smith the title of Doctor of Laws (LL.D.). At the end of 1763, he obtained an offer from British chancellor of the Exchequer Charles Townshend—who had been introduced to Smith by David Hume—to tutor his stepson, Henry Scott, the young Duke of Buccleuch as preparation for a career in international politics. Smith resigned from his professorship in 1764 to take the tutoring position. He subsequently attempted to return the fees he had collected from his students because he had resigned partway through the term, but his students refused. Tutoring, travels, European intellectuals Smith's tutoring job entailed touring Europe with Scott, during which time he educated Scott on a variety of subjects. He was paid £300 per year (plus expenses) along with a £300 per year pension; roughly twice his former income as a teacher. Smith first travelled as a tutor to Toulouse, France, where he stayed for a year and a half. According to his own account, he found Toulouse to be somewhat boring, having written to Hume