Anyone who merely turns the pages of this new edition will find that 48 percent of the fig ures are familiar to him from the third edition. But whoever reads it will discover that no three consecutive pages of text have been transferred unaltered. The enormous development that has taken place since 1950, particularly the surprising extension in the practical applica tions of micrometeorology, have made it necessary to rewrite the book. In producing this work, I had in mind two aims which were linked more closely to each other than I had at first dared to hope. The new edition was to be a...