This book contains the second of the two series of Gifford Lectures which I was invited to give at the University of Aberdeen, Scotland, in the years 1970 and 1972. The first series, entitled “Critique of Heaven”, was published in 1972. “Critique of Earth” is the title of this second series, thus completing the overall theme “Critique of Heaven and Earth”. In addition to the expression of my sincere gratitude to the Senatus Academicus of the University of Aberdeen for the renewed hospitality I enjoyed during the weeks spent at the University in 1972, I wish to thank the Gifford Lectures Committee at Aberdeen for the generous subvention which paved the way for this second volume to be published.

A. Th. VAN LEEUWEN

Gendt (Gld.), Netherlands, Summer 1974