So far as the colour plates in this volume are concerned, we owe an incalculable debt of gratitude to Ian D. Huntley, A.M.R.Ae.S., whose extensive researches have provided the basis for all of the colour work in this volume. A short account of Ian Huntley's researches - and a few of the results that they have yielded - appear in the Appendices. These, if read in conjunction with the notes on page 16, should obviate a number of misconceptions which apparently confused some readers of the first edition.