A number of significant changes have occurred in Advances in Solar Energy since Volume 1 appeared in 1982. The delays in publication of the second volume are the result of reorganization of the American Solar Energy Society, and the negotiation of a new publishing arrangement. Beginning with this volume, Advances is now published jointly by the Society and Plenum Press. The Editorial Board has been enlarged to be more representative of the different fields of solar energy conversion. Production of Advances is being expedited through the use of modern word processing equipment and the 'lEX typesetting-editing program. We have gone to a single-column format to ease the problems of presenting long equations, and we expect that the user of the volume will find it easy to read. The use of 'lEX will make last minute updates possible. The external appearance of the volume matches that of Volume 1. We expect that future volumes of this annual will be proceeding on schedule. We invite comments from users and correspondence from prospective authors of critical reviews. Karl W. Boer John A. Duffie CONTENTS CHAPTER 1 The Measurement of Solar Radiation Ronald Stewart, Daniel W. Spencer and Richard Perez 1.1 Abstract 1 1.2 Characteristics of Pyranometers ....................................... . 2 1.3 General Features of a Pyranometer ................................... . 3 1.3.1 Instrument Sensitivity 4 1.3.2 Response with Time 4 1.3.3 Sensitivity 4 1.3.4 Responsivity ................................................. .