Early in 1750 David Hume sent Oswald the manuscript of his well-known essay on the Balance of Trade, afterwards published in his _Political Essays_ in 1752, asking for his views and criticisms; and Oswald replied on the 10th of October in a long letter, published in the _Caldwell Papers_,[25] which shows him to have been already entirely above the prevailing mercantilist prejudices, and to have very clear conceptions of economic operations. He declares jealousies between nations of being drained of their produce and money to be quite irrational; that could never happen as long as the people and industry remained. The prohibition against exporting commodities and money, he held, had always produced effects directly contrary to what was intended by it. It had diminished cultivation at home instead of increasing it, and really forced the more money out of the country the more produce it prevented from going. Oswald's letter seems to have been sent on by Hume, together with his own essay, to Baron Mure, who was also interested in such discussions. The new light was thus breaking in on groups of inquirers in Scotland as well as elsewhere, and Smith was from his earliest days within its play. Amid the more serious labours of these literary and economic lectures, it would be an agreeable relaxation to collect and edit the scattered poems, published and unpublished, of Hamilton of Bangour, the author of what Wordsworth calls the "exquisite ballad" of "The Braes o' Yarrow," beginning-- Busk ye, busk ye, my bonny, bonny bride, Busk ye, busk ye, my winsome marrow, Busk ye, busk ye, my bonny, bonny bride, And think no more on the Braes o' Yarrow.