 A year after his arrival, he delivered Harvard’s prestigious Lowell Lectures. The lectures formed the basis for Science and the Modern World (1926). The 1927/28 Gifford Lectures at the University of Edinburgh followed shortly afterwards and resulted in the publication of Whitehead’s most comprehensive (but difficult to penetrate) metaphysical work, Process and Reality (1929c). And in the Preface of the third major work composing his mature metaphysical system, Adventures of Ideas (1933), Whitehead stated: