Acknowledgements

The author wishes to express his thanks to the persons whose help was especially important in preparing this publication :

Prof. Jerzy Dobrzycki, Academy of Sciences, Warsaw, Poland,

Dr. Jean-Michel Faidit, Planetarium Montpellier, France,

Dr. Mikhail L.Gorodetsky, Moscow State University, Russia,

Dr. Hermann König, Mathematisches Seminar der Universität Kiel, Germany,

Carles Schnabel, Agrupación Astronomica de Sabadell, Spain,

Prof. Frank R. Stephenson, University of Durham, United Kingdom,

Prof. Leslie V. Morrison, Pevensey, East Sussex, UK; formerly Royal Greenwich Observatory,UK,

Alexander Pratt, IOTA/ES, BAA, Leeds, West Yorkshire, U.K.