preface to the Second Edition vii The editors wish to express their gratitude to Mrs. Connie Gaskill of Heinkel Filtering Systems, Inc, for the wordprocessing assistance she gave to this edition Scotch Plains, New Jersey Henry C. Vogel Bridgeport, New Jersey Celeste L. Todaro September. 1996Preface to the Second Edition vii The editors wish to express their gratitude to Mrs. Connie Gaskill of Heinkel Filtering Systems, Inc., for the wordprocessing assistance she gave to this edition. Scotch Plains, New Jersey Bridgeport, New Jersey September, 1996 Henry C. Vogel Celeste L. Todaro