The Fire within the Eye: A Historical Essay on the Nature and Meaning of Light

Abstract

Since the dawn of history philosophers have sought to explain vision and the behaviour of light. David Park ranges across almost 25 centuries from the Ancient Greeks to quantum optics and lasers. Philosophical ideas dominate the first half of the book, giving way to physics in the later chapters. The oldest and longest lasting theory of vision proposed a `visual ray' emanating from the eye, somehow sensing the object and returning through the pupil to create an image. It was challenged by an alternative idea that every object gave off some sort of ghostly matter that carried information to the eye. Neither theory had any obvious role for light in the process of vision, but a role had to be found, since we cannot see in the dark. The basic ideas of geometrical optics were known, but the metaphysical role of light was more important, especially for the early Christian church. The light shining in the darkness was a metaphor for good overcoming evil, and much intellectual effort was spent on elaborating on the light of creation in the Genesis story. Greek and Roman knowledge was lost in Europe during the Dark Ages but came back via Islam and the Arab world, so that Aristotelian philosophy was the norm up to the scientific revolution. Despite all attempts by the established authorities, the ferment of new ideas could not be stopped. Newton's Opticks offered the first comprehensive modern study of light, but it established a new orthodoxy lasting until the 19th century, when the wave theory of light finally ousted the particle theory. Maxwell's theoretical insight linking light to the electromagnetic field seemed to have settled the problem once and for all, but in this century quantization and wave-particle duality have provided a twist in the tail of the story. Park's approach is intentionally discursive. This helps to clarify the connections between events which are more often described in isolation from one another. It also dispels many of the simplifying myths that have become accepted in conventional accounts. Newton came down in favour of the particle theory of light, but he was not as firmly attached to it as is generally thought. He endowed the particles with bizarre properties more akin to those of waves in order to explain the interference and diffraction phenomena. Newton provoked some strong reactions, notably from Goethe, whose curious Theory of Colour shows that, as late as the 19th century, philosophers still felt they could challenge mathematicians in explaining science. The difficulty with the discursive approach is the concentration needed to follow the story through all its twists and turns, especially in the early chapters where the concepts are unfamiliar. Major themes become entangled with the many side tracks and with Park's own commentary. In an American book one expects American spellings, but occasional colloquialisms jar badly. Referring to venerable philosophers by their given names is particularly irritating. It is surprising to see an author who is an Emeritus Professor of Physics using the term `focal point' incorrectly, and confusing real and virtual images, even if it shows nothing more than poor proof-reading. The lengthy bibliography is evidence of the author's extensive research, but it is not a book intended for the scholar. Some effort has been taken to make the book accessible to readers with no scientific training, there are almost no equations, and technical terms and usages are explained, but it is not popular science either. It is too long and complex for that, and in many respects it is a very personal testimony. One would hesitate to recommend it to any but an exceptional student. Science educators would benefit from the breadth of background information it provides, but it is the sort of improving reading that, sadly but inevitably, is neglected in today's pressured world.