But this mathematical _brochure_ imperfectly represents the ‘intense study’ at New Machar. For an event happened soon after Reid’s settlement there which determined the direction of his thoughts for the remainder of his life. In January 1739, a book made an almost unnoticed appearance in London, which in the end became the chief factor in shaping the course of European thought. Its author was David Hume, then a young man, unknown to fame, not thirty years of age, the younger son of a Berwickshire laird. Hume was younger than Reid by one year: both were born on the 26th of April. His name is popularly connected with the _History of England_; but this _Treatise of Human Nature_, which somehow found its way into the manse of New Machar, represents his most significant work. It has contributed perhaps as much as any single book to the subsequent progress of philosophy in Europe. Hume indeed penetrates into regions which the ordinary reader fails to connect with everyday interests of life, or with the hopes and fears of human beings. Accordingly, as he tells, the _Treatise_ ‘fell dead-born from the press, without attaining such distinction as even to excite a murmur among the zealots.’ In a letter to his friend Henry Home, afterwards Lord Kames, written soon after this explosive mixture had been applied, its author announces that the issue was ‘but indifferent, if I may judge by the sale of the book, and if I may believe my bookseller. I am now out of humour with myself; but doubt not in a little time to be out of humour with the world, like other unsuccessful authors. After all, I am sensible of my folly in entertaining any discontent, much more despair, on this account, since I could not expect any better from such abstract reasoning.’ This book, which professes to explain ‘human nature’ as a fact in the universe, conducts to a final paralysis of human intelligence in universal doubt.