Natural colour

Introduction

Starting with a teenage fascination with astronomy and the sky I have, more or less continuously through the years, cultivated and enjoyed an interest in observing natural phenomena - especially those concerning colour. While at school in Essex, one of our two physics teachers introduced me to Minnaert's wonderful book Light and Colour in the Open Air and I still find it hard to observe a phenomenon which is new to me but not described somewhere, however fleetingly, in that work.

Minnaert professed techniques for observing nature which involved mostly the naked eye and, occasionally, only the simplest of instrumental tools. My own particular developments have been largely in the use of spectroscopes for observing the colours of natural (and sometimes man-made) objects and phenomena. I have collected a number of these devices - which are not easy to find - at various times and have made a catalogue of them here with some hints about how to get hold of those which are still available.

While having a professional interest in astronomical spectroscopy with the privilege of using some of the world's largest telescopes, I have been thrilled by the stories which can be told by visual observations of the spectra of objects as diverse as eggshells, earthworms, bird feathers, seaweeds and gemstones. These appear as colour images projected onto the retina rather than annotated plots on a computer workstation and, as such, carry their own special beauty.

These pages are not only about spectroscopy however. Over the years I have kept a series of notebooks describing my observations and the task has been to organise this material in some reasonably connected way and to make some of the sketches and photographs available. The prospect of a 'linear' organisation into a series of headings and sub-headings has, however, always acted as a hinderance to the collection of the material and I found the prospect of using a hypertext scheme particularly appealing. One of the excitements of the subject is the existence of unexpected connections and analogies across a wide range of subject matter which can be established so directly using this technology.

During the early years, I was reluctant to take photographs to illustrate what I had seen; preferring to take notes and make sketches. Recently however I have begun to realise what was being lost by this omission and so I have started to use a camera to explore new areas of natural observation. The images should at least make these pages more visually appealing and I often use them as a way to introduce discussions of some of the physical processes at play. Some of the sketches, particularly those of spectra, have been scanned and so appear here as black and white, and occasionally colour, images.

The photograph which heads this page - a seaweed-clad groyne on the beach at Bexhill in Sussex, England - will serve as the introduction to our story since it illustrates, with rather dramatic effect, some of the mechanisms generating the colour which delights our eye.

In order to allow rapid access to particular topics, I have included a table of contents.