The brain's adjustment of visual input has been a vital field of study for neurologists over the last twenty-five years. In 1973, Semir Zeki isolated a bean-sized area of brain cells in the prestriate cortex of the brain, that seemed responsible for creating colour impression, and named it V4. (This area responds to magnetism by generating colour hallucinations.) It receives its input from V1 cells in the primary visual cortex, where wavelength information is converted to some form of neural impulse that can be handled by V4. Another neurologist, Oliver Sacks, explored the implications of this discovery in "The Case of the Colourblind Painter". When the painter, Jonathan I, lost his colour vision at the age of 65 (after a car accident), not only did he lose colour from his normal vision but his dreams turned to black-and-white. Sacks inferred Mr. I's V4 centres had been knocked out, proving that V4 was responsible not only for formulating colour impressions of the outside world, but was also the source of the internally-generated colours of hallucinations. Drawing on several cases, Sacks concluded that colour vision is highly dependent on V4, whose function was automatic rather than learned. While this might suggest that the brain performs simply another process in the mechanistic processing of light, Sacks was careful to point out that none of this limits the interpretation and meaning of colour:

"V4 may be an ultimate generator of colour, but it signals to and converses with a hundred other systems in the mind-brain, and perhaps it can also be modulated by these. It is at higher levels that integration occurs, that colour fuses with memories, expectations and desires to make a world with resonance and meaning for each of us."

Such nice distinctions are preserved, to account for both the brain and the mind. Beyond the eye, and on through the tangle of nerves that lie behind, the effects of light have consequences at the highest level - that of human consciousness. Neurological research into vision, and the other senses, can directly impact on psychology and psychiatry. It may even encroach on the traditional preserves of philosophy and religion. Then, a metaphysical tendency emerges, in an attempt to account for the unknowable and the yet unknown. Speculations of this kind have resulted in a spate of quasi-theological works, authored by members of the scientific community. Their interests extend to embrace nuclear physics and astrophysics where, yet again, light (and therefore colour) have critical roles to play. It is true that many neurologists are more prosaic, believing all thought processes will one day be explained by mere electro-chemical actions in the brain. In any case, the study of human consciousness has become a core topic in neurology. The public, inexpert though it may be, is never immune from such debate: it is crucial in the investigation of how we perceive ourselves, and understand the world around us. Nor is the study entirely new - the senses were traditionally considered to provide important clues to our reality. The path of sensation, from the external world to the mind (and even the soul), had eagerly been traced by Plato and Aristotle, by Descartes and Newton.

It has long been held that appropriate sensations had positive effects, that colours or musical notes, when properly chosen, gave pleasurable harmonies. Early in the 20th century, Professor Rimington suspected there may be "some common foundation or organic basis in nerve structure, or in mental constitution for receiving both colour and musical impressions". He supplied his own common law for vision and hearing, with a colour-music code for use on the colour organ. It was based on a correspondence between their vibrations, a not unusual presumption. After all, light (and its colours) were considered to travel in waves through an imaginary aether, just as sound waves moved through the air. An invisible world, in constant orderly motion, had become a scientific reality in the 1860s, when James Clerk Maxwell formulated the electro-magnetic field. Who knew what else was out there - the spirits of the dead? a fourth dimension? a universal consciousness? Even today, attempts to explain puzzling physical phenomena can give rise to all-embracing philosophies, couched in the mystic language of vibrations. That colour could accommodate spiritual interpretations, as well as convey decorative feelings, was an idea that sat easily with Roy De Maistre. His colour-music code was intended for the wider purpose, as is clear from his speech at the opening of the "Colour in Art" show of 1919:

"What is colour? Many accept it unquestioningly - a few, I believe, are almost unconscious of its presence - for others, it constitutes an aesthetic pleasure or an interesting scientific phenomenon - the result of light vibrations acting upon their optic nerves. But there are many for whom Colour means far more than this - to them, it brings the conscious realization of the deepest underlying principles in nature, and in it they find deep and lasting happiness - for those people, it constitutes the very song of life and is, as it were, the spiritual speech of every living thing."

De Maistre's exhibited work included five colour schemes for interiors (in collaboration with Lloyd Rees), elaborating ideas he had developed while designing therapeutic colour interiors for psychiatric hospitals. His passion for colour music, that saw him creating spectral keyboards (in association with Adrien Verbrugghen), culminated in the colour-music charts he put on display. With these coded arrangements, he attempted to supply a working system, to mathematically calculate colour harmony. Teaching at Sydney's Royal Art Society in 1913, Anthony Datillo Rubbo expressed similar concerns. He emphasised the interpretive role of the mind, maintaining that colour was in fact an internal sensation caused by light impressions received through the eyes and transferred to the brain. He acknowledged that colour effect was caused by light waves, as science described, but like the more painterly Goethe, he held that local colours were chiefly illusory. Rubbo's theories influenced several of his students to revolutionize their use of colour - the bright, sumptuous palettes of Grace Cossington-Smith and Roland Wakelin are due in part to his tutelage. Wakelin in turn had a liberating influence on Roy De Maistre, his co-exhibitor in 1919, though De Maistre's interests extended far beyond the confines of art school theory.

De Maistre was a regular at the extended lunches Rubbo held at his studio and, at one of these, the Australian artist, Margaret Preston, gave a talk on her colour chart. It was covered by a cardboard wheel with holes cut in it; when the wheel was turned, colours appeared in the open spaces and helped Preston decide on the colour schemes for her paintings. Her device may have served as a prototype for De Maistre's similar Colour Harmonizing Chart, though there were other exemplars around. Alexander Hector, the Sydney colour organist, owned a colour wheel contrived by the South African scientist William Fraetus, in 1911. Intended as a key to the science of universal vibrations, its colours were given musical notes - as well as star signs and mysterious geometrical figures - from which major and minor keys were selected by rotating masks. In the United States, a more rational colour chart was marketed as the Taylor system. Of rectangular (rather than circular) form, a mount was moved over its surface, exposing different colour keys through small cut openings. In England, a Mrs Sargent Florence had constructed her own private colour-music wheel, with twelve colours painted round the rim of a celluloid disk. She supplied no less than eight rotating masks, to pick out various chords as well as major and minor keys. While her disk was similar to De Maistre's commercial chart, her additional masks made harmonic colouring more explicit.

The comparative frequencies of colours and musical pitches, had been earnestly debated from the beginning of the 19th century. It was common knowledge that the frequency of a musical note was doubled, to achieve its octave. However, since Thomas Young first calculated the frequencies of colour in 1801, it was found that violet had less than twice the frequency of red. The spectrum fell short of a 'colour octave', and Young considered it to be more akin to a minor sixth. To accommodate the scientific fact, several inventors of colour-music codes abbreviated the Newtonian spectrum to ROY G BV. They omitted indigo (as Preston was to do) and added an extra colour at the end of the scale to make up the shortfall.

In "The Laws of Colour Harmony" of 1881, Theodor Seemann allocated ROY G BV to white notes of a C scale, "in their vibrational order as in music". He limited the spectrum to the notes from C and A, and filled the void on B with black (preceded by a brown on A#). Mrs J F Hughes was to follow the same basic array in 1883. A cousin of Charles Darwin, she fittingly called her essay "Harmonies of Tones and Colours Developed by Evolution". Blue and indigo were combined on note G, followed by violet at A. B was ultraviolet, rightfully not a colour. It could be a symbolic greyish-violet, descending into black; likewise, yellow may ascend to white. The two colours (on notes B and E) represented the extremes of darkness and light. Hughes was hoping "if, therefore, musical harmonies are correctly gained, the same laws will develop harmonies of colour and will agree with the colours of the rainbow".

Mrs Sargent Florence adopted a similar tactic, excluding indigo and placing the colours ROY G BV on the white notes of a C major scale. With violet on A, the remaining note B was occupied by an additional purple. Margaret Preston followed suit, with one further alteration - the note F was assigned yellow-green instead of green, and a green-blue was given to F#. Preston's arrangement gave a symmetrical balance between yellow on E and a blue G (though it seems unfortunate that a painter of flowers and vegetation should omit pure green). The remaining 'black' notes took up intermediate hues, half way between the main colours of adjacent white notes. For instance, Preston's C was always ruby red and D orange: the semitone between them had a somewhat indefinite character. The black note C# was orange red or scarlet, but became red orange or flame when considered as a D flat. Otherwise, the Newtonian emphasis is clear - main colours occupy white notes of a musical scale, and the key chord (a C major triad of C, E, and G) is picked out in painters' primaries of red, yellow and blue. The same triadic colours held in Newton's original system and in De Maistre's colour-music code, even though their key chords were D minor and A minor respectively.

Henry Fitch Taylor attempted to space the six primary and secondary colours more evenly, a musical tone apart. Adding six more intermediate hues, he allocated the twelve colours to twelve semitones in a scale, starting with red at C. Bainbridge Bishop had used identical coding for his colour organ, co-ordinating each note to a glass filter and projecting coloured light on a screen. When he wrote of his invention in 1893, all his machines had gone up in flames, including the organ owned by the showman P T Barnum. (Perhaps it was faulty electrics.) He had to be content with rhapsodizing on the Harmony of Light and the Soul of the Rainbow, comparing successive octaves to different kinds of bows. Despite his old-fashioned language - where blue-violet and indigo were interchangeable terms, as were yellow-orange and gold - his colour-music code was as logical as the Taylor system. Both relied on words from simple paint mixtures to divvy up the colours, as if such divisions were equal. Neither resorted to wavelength descriptions, but trusted the painterly convention to iron out the colour-music code. But what would Margaret Preston care, when six colours from her code could turn her mood to Japanese? Then she could add - to the traditional pentatonic scale of C, D, E, G, A - her own F#, of colour sometimes peacock...well, there's a typical modern gal for you.

As for Roy De Maistre: our hero wielded his code like a mighty sword, in defence of both tradition and modernity. He remained committed to a belief in ancient indigo, alone uniting it to F. it was said he had special powers. According to rumour, De Maistre saw coloured visions when listening to music. Both harmonies and melodies appeared in colour, and identical visions re-occurred when he heard the same music again. Others have reported similar experiences where not only music, but also letters and numbers take on colours. The colours remain consistent for each person throughout their life, appearing in the mind's eye or as if projected on a screen in front of the person's eyes. These combined sensory responses to otherwise ordinary stimulation are clinically defined as synaesthesia. Other audio-visual hallucinations (from drugs, sensory deprivation, migraines, and dreams) are less predictable, more subjective, tending to overwhelm reality rather than supplement it. Still, they bear a qualitative resemblance to synaesthesia: these experiences can be so convincing that the hallucination appears to come from an outside source as part of the real world. The neurologist Richard Cytowic has described this experience as noesis, the same feeling that gives significance and importance to mystical religious experiences. He suggests that hallucinations can be so convincing that some people may be eager to yield to cosmic or theological explanations for the authority of their visions. As a corollary, one might describe any courting of psychedelic experience, or a fascination with synaesthesia, as a search for noetic meaning. In 1968, Lawrence Durrell put it rather differently in his novel "Tunc":

"How sad it seems that we, images of pathetic spoonmeat, spend our time in projecting such strange figures of ourselves - delegated images of a desire perfected. The mystical gryphus, the 'perfect body' of Alexandrian psychology, is an attempt on a tele-noetic field. (What space is to matter, soul is to mind.) Some saints were 'dry-visioned'. (Jerk, jerk, but nothing comes; taking the 'distressful path' towards after-images of desire.) They were hunting, poor buggers, for a renovated meaning or an infantile adoption by a God. Unhappily, words won't carry the charge in these matters, hence the deficit of truth in all verbal fields. This is where your artist might help. "A craft is a tongue, a tongue is a key, a key is a lock." On the other hand a system is merely the shy embrace by which the poor mathematician hopes to persuade his bride to open up."

Like Durrell, other writers have looked to visual artists for 'images of desire perfected'. The Roman author Ovid gave the task to Pygmalion, a legendary sculptor who fell in love with his own statue of the female form. When she came to life, the artist's lone act of creative imagination became a reality. The legend flatters the skill of any artist, exulting artwork as more excellent than nature. But Pygmalion stopped short of the supreme act of creation. Divine intervention was required, so the goddess Aphrodite took pity on Pygmalion's yearning and gave life to his ivory carving. It is little wonder Ovid's story has been a popular subject for artists. Other god-like powers (with the brush rather than the chisel) were celebrated in Dosso Dossi's "Jupiter, Mercury, and Virtue", of the 1520s. Dossi handed the artist's role entirely to the pagan gods, in a charming tale of Jupiter painting the wings on butterflies. More than four hundred years later, the Surrealist Remedios Varo depicted a similar act of creation (shown below), this time with birds. Both painters allowed the viewer to take flight into a mystical past, an alternative reality - perhaps they are keys to the kind of tele-noetic field that Durrell hankered after. Certainly Varo's owl-like figure could be an exotic incarnation of the mystical gryphus, the 'perfect body' aimed for by the Alexandrian arts of spiritual alchemy. And Varo's act of imagination surely placed her in the self-same role, extending her own noetic field by committing it to canvas. Some of the picture's mystery is stripped away when its occult conventions are uncovered. For example, both colour and music are essential to Varo's system, as raw materials and a guiding principle. She invoked their power, and the mystique of a colour music tradition stretching back, in some form, for more than two millennia. (A similar conventional authority might be imputed to De Maistre, although his relation of colour to music was more literal and direct, and provoked no act of magical creation.) Whether such paintings can convince the unbelieving viewer, or even enhance their creators' spirituality, is uncertain. Still, a painting is more concrete expression of beliefs than mere lip service, and an artist would appear better off than Durrell's shy scientist or benighted saint.

Illustration 3 : "CREATION OF THE BIRDS", Remedios Varo, 1957.

In her painting-within-a-painting, Remedios Varo has credited the creation of birds to the brush of a fellow artist, in the guise of an owl. On the left is a gourd-like apparatus, an animistic variety of alchemical furnace, said to manufacture the life-giving Philosopher's Stone. Its shapes are redolent of the Gnostic egg, from which a multi-hued peacock hatched at the creation of the universe. Fed from the outside world, it pumps the artists' primary colours of red, yellow and blue onto a painter's palette. A violin hangs like an amulet over the bird-painter's heart, and its harmonic principles are channelled through a conduit to guide the artist's pen. With its right hand, the bird-painter is still completing a drawing of a bird with the magic pigments, just as it springs to life under the enlivening influence of spectral rays. These originate from the light of a star, refracted by a prism in the painter's left hand before falling on the work in progress. Music and colour, as sacred ingredients of the anima mundi, enable the bird-painter to harness the life force, creating colourful songsters after its own image.

Since neuroscience teaches that mind and body are, to some degree, inseparable, some of its practitioners try to quantify the effects of spirituality. Herbert Benson, an Associate Professor at Harvard and author of "Timeless Healing", is presently running controlled experiments to assess the effect of prayer on coronary bypass patients. Yet other scientists have run tests on epileptics prone to ecstatic seizures, isolating a place in the brain that lights up during convulsions. They found it to be active in deeply religious people when prompted by mystical thoughts, so they dubbed it the 'God spot'.

Neurology seems to suggest some conjunction of any visionary impulses with religiosity: De Maistre's work might serve as a convenient example. His colour music painting coincided with periods when he seemed most moved by the religious spirit - as a proto-spiritualist in Australia and as a Catholic convert in England. But Cytowic paints a more complex picture of synaesthesia. He speculates holistic perception, in which all the senses participate, is perhaps a primitive mode of cognition present in all of us. For most people, reason and logic functions in the cortex, the outer surface of grey matter, dominate their perceptions. Synaesthetes have a less differentiated understanding; they do not filter their surroundings and order their responses to the same degree. Established triggers (music in De Maistre's case) affect the seat of memory, emotion and relevance in the limbic system, the relatively unevolved region around the brain stem. Cytowic believes that emotive limbic activity drives general brain functions in all people, but sometimes produces hallucinations in synaesthetes. It may be that De Maistre's colour music paintings originated partly from such visions - that he had the capacity to harness his primitive perceptions and this fed his art.

Hallucinations, such as De Maistre may have experienced listening to music, were systematically recorded as early as the 19th century. Synaesthesia (where one sense triggers off a response in another) is found in about one person in every 25,000. The painter Mr. I, for one, had experienced a rich tumult of colour in response to different musical tones; when he became colour-blind, these subjectively-experienced colours disappeared. The neurologist Sacks concluded the effect was dependent on the V4 nerve centre in the brain (as was the similar colouring of dreams): after Mr. I's accident, his damaged V4 could no longer effectively respond to aural stimulation, ending his coloured visions.

Sacks implies that intra-brain signals had been exchanged between the separate sections of the brain controlling visual and aural impressions - in fact, studies of the congenitally deaf demonstrate that these same stimuli can effect unexpected regions of the brain. It was found that the areas of the left temporal lobe, assigned a purely auditory function in hearing people, were re-assigned for vision processing and became highly active when sign language was used. In contradistinction, the keen hearing of many blind people is often used to supplement their visualization of the world (in responding to the acoustic 'shape' of a room, for example). Researchers at Manchester University's Department of Optometry aim to enhance this skill, with a musical language intended to describe shapes for the blind. Each aspect of a shape is associated with a particular sound that can be written on a music stave; playing back the sounds could paint a picture of even complex objects. Experience of this system might be likened to synaesthesia - albeit to a formalized, learnt variety - though one wonders how an adept's appreciation of music might be affected.

It seems clear the brain is highly flexible - not just a universal machine with pre-programmed, hard-wired centres, but a malleable entity, taking different forms according to the way it is sculpted by experience and the demands placed on it. The deaf and the blind seem able to realign brain functions through practice, prompted by necessity. Less voluntary responses occur in synaesthetes' brains - there are some indications the condition could be hereditary - but they follow orderly patterns, intermingling their reactions to set sensory inputs. Quite different are the hallucinations of auditory schizophrenia; these are not prompted by external stimulation of one of the senses. But MRI scans taken at Melbourne's Mental Health Research Institute have shown that activity in the auditory cortex accompanies the schizophrenic episodes. It seems the brain is capable of generating seemingly real sensations of its own accord, an experience that most of us become aware of only in dreams. While we rely on our sensory perceptions to regulate our waking hours, it is likely that some consensual view of reality constrains our fullest responses and kerbs the imagination. After all, a vast array of possibilities is available to any brain, through the variety of connections that trillions of neurones provide. Some intra-brain linkage of the senses is feasible, even probable, in many individuals and more precise neurological explanations may emerge to account for some perceived similarities in the experiencing of colour and music.

It is tempting to see, in the phenomenon of synaesthesia, a genuine source of a colour music experience. Indeed, current understanding of synaesthesia has reignited interest in putative links between music and colour, as they are deployed in the arts. Just so, studies of synaesthetes in the late 1800s had formed a backdrop for major overhauls in aesthetic attitudes in the early 20th century. Colour-music codes, however, do not provide reliable guides to synaesthesia; rather, they seem didactic exercises, bound by rules and historical precedents, shrouded in visionary import and formalistic interpretations. Some intellectual systems, such as the "modes of limited transposition" employed by Olivier Messiaen, to compose music akin to his personal visions, come closer to providing an individual testimony to synaesthesia. But orthodox colour music has proven resistant to even fundamental shifts in scientific thinking, encumbered as it is with its metaphysical agenda. It is unlikely to respond to any fresh biological imperatives based on the neurology of synaesthesia.

More contentiously, subjective experiences were tellingly described in "Thought Forms", co-authored by the Reverend C W Leadbeater and Annie Besant in 1901 under the auspices of the Theosophical Society. Their visions of music were attributed to clairvoyance rather than synaesthesia, and claimed as evidence of a cosmological order connecting a variety of physical and psychic phenomena. For one of Mendelssohn's "Lieder ohne Wörte", the four-part harmonies would appear as lines of blue, crimson, yellow, and green. The whole spectrum combined in the "Soldiers' Chorus", from Gounod's "Faust", and radiated in a sort of expanding globe. Wagner's "Meistersingers" provided a vision like rolling clouds among mountain crags, suspended in the air. Its overall colour was a sum of the parts, as the colours of melody, chord, and phrase combined for each theme. Individual notes became lost in the more complex music, though their iridescent hues still flickered across the apparition, "as they do over the surface of molten metal". Each display represented the individual composer's thoughts, but any mistakes in the performance would also be visible. The intent of a piece of music, for better or worse, was sensed through its vibrations - perhaps even by those beyond audible and visual range. The ancient Chinese had a different purpose and method for 'reading the air'. Before a battle, the shaman was called to assess the ch'ii, or vital force, rising heavenward from the opposing army. He communicated with it, by playing his pipe toward the air above the enemy. A similar idea moved Louis-Bertrand Castel to build the first colour-music instrument in Europe, in the second quarter of the 18th century. Castel's 'harpsichord for eyes' was inspired by a passage from "Musurgia universalis", written by his friend Athanasias Kircher in 1650:

MENDELSSOHN	GOUNOD	WAGNER

Illustration 4 : THEOSOPHICAL FORMS BUILT BY MUSIC,
from "Thought Forms", by A Besant and C W Leadbeater, 1901.

According to Theosophists, visions would appear in the air above a source of music. The apparitions were purported to demonstrate the hidden but true form of the music, discernible by the privileged few with the gift of second sight. In this case, they originate from an organ inside a church; both shapes and colours vary throughout the performances, according to the type of music being played. Generally, size increased with volume - the 300-foot church tower gives an idea of scale - while texture varied with the timbre of the instrument. Each note formed a short line with its own colour, and Leadbeater clearly believed in some specific colour-music correspondence. But he refrained from assigning particular colours to definite pitches. Even in short melodies, the details of colour and note somehow became combined, blending together to achieve overall hues for each melody, chord, or theme.

Newton himself expressed puzzlement regarding "by what modes or action (light) produceth in our minds the phantasm of colour". He had stressed mechanistic processes, examining light as an objective and external phenomena that had no colour in itself, simply the capacity to differently affect the retina which then transferred colour impressions directly to the brain. Some noticeable effects - coloured shadows and after-images - could not be accounted for by Newtonian optics; the ability to dream in colour was certainly not to be explained by the impact of a variety of particles on the retina. Colour impression is a subjective matter, and the continuous flow of spectral colour is usually interpreted by common understanding, to isolate different colours. The human eye can distinguish over 130 hues in the spectrum alone, but selection amongst them is subject to personal, cultural and practical considerations. At the end of the 18th century, the Romantics favoured the personal approach, and reacted to the impersonal science of the Enlightenment. William Blake railed against 'Newton's sleep' while J W von Goethe pilloried Newtonian optics in his 1810 "Theory of Colours". The basic tenets of the colour-music code came under specific attack when Goethe wrote on colour in Relation to the Theory of Music:

"That a certain relation exists between the two, has been always felt; this is proved by the frequent comparisons we meet with, sometimes as passing allusions, sometimes as circumstantial parallels...Colour and sound do not admit to being compared together in any way, but both are referable to a higher formula, both are derivable, though each for itself, from this higher law. They are like two rivers which have their source in one and the same mountain, but consequently pursue their way under totally different conditions in two totally different regions, so that throughout the whole course of both no two points can be compared. Both are general elementary effects acting according to the general law of separation and tendency to union, of undulation and oscillation, yet acting thus in wholly different provinces, in different modes, on different elementary mediums, for different senses."

Goethe had opted for an approach reclaimed from the past, from Aristotle's assertion that all colour could be understood as the interaction of light and dark. Goethe represented their opposing forces by two fundamental colour primaries - yellow and blue. (Belatedly, he included red as an 'augmentation' of these, and green as a diminished variant.) But, unbeknownst to Goethe, the laws of optics were being rewritten: Huygen's neglected wave model of light was dusted off as Newton's theories came in for an overhaul. The corpuscular theory of light was overthrown, when Thomas Young and Augustin Fresnel found ways to measure its wavelengths. Young also explored the way light interacted with the eye: he postulated that nerve filaments on the retina were sensitive to three wavelengths only. Thus, the combined frequencies of red, green and blue-violet accounted for all the colours we see. By comparing the vibrations of colour and sound, Young re-evaluated Newton's colour music. He found the spectrum equivalent to a major 6th, at best, rather than a full octave, and concluded that "any attempt to produce a musical effect from colours must be unsuccessful, or at least that nothing more than a very simple melody could be imitated by them". Musical ratios were no longer needed to separate colours, whose locations were given by Fraunhofer lines - thin dark bands discovered at fixed positions in the spectrum. Scientists could plot accurate divisions in wavelengths, without resorting to vague colour names.

The most formidable barrier to the advance of science was from traditional art practice. The new theories proved inapplicable to the palette, since the coloured lights of prismatic experiments behave differently to paints. Their mixtures add the brightnesses of colours together, and Young's red-green-blue primaries together make white. The basic pigments, however, are red, yellow, and blue. When mixed, they give a darker result than the brightest component, and all together yield a dark and neutral shade (a theoretical black). Yellow, as the brightest colour, had always to be included in any set of painter's primaries since there is no way to mix up to it. On the other hand, yellow would be pretty useless as a primary of light. The spectrum can be paraphrased in paint, by blending primaries, two at a time, for secondary colours of orange, green and purple. The sequence of six hues resembles Newton's ROY G BIV, so artists simply removed indigo from Newton's colour wheel, to turn it into a paint-mixing diagram. In an irony of history, the colour-music code persisted, as the Newtonians' second line of defence. Its metaphysical implications were promoted in standard texts at art colleges and, as a guide to colour harmony, colour music proved most useful to aesthetes and academics musing on its abstract possibilities.

The primary colours held pride of place for Field; they had melodic and harmonic significance and symbolized the Trinity. From darkest blue, through central red to lightest yellow, the primaries occupied musical notes of C, E, and G, which make up the C major chord. Intervening notes, of D and F, were given the appropriate secondary mixes of purple and orange. The remaining secondary was split into yellow-green and green, to fill out the scale at A and B. In Field's beautiful hand-tinted plate, varieties of his colours descend into darkness, for two-and-a-half octaves of the C scale. In painting, light and dark shades represented high and low pitches, respectively, while the spacing of colours within a picture was equivalent to the element of time in music. (Many artists, including De Maistre, followed the same general principles.) Having established his analogy of primary colours and the C chord, Field searched for equivalents in the other arts. In drawing, he found a 'tri-unity' of forms - the arc, angle, and line - and in poetics, the three vowels O, A, and I (probably singled out for their shape as much as their sound).

Owen Jones consulted Field's ideas on colour harmony when designing the interior of the Crystal Palace, in 1850. Trials of the colour scheme excited a great deal of public debate and the primaries of blue, yellow and red were eventually accepted. In proportions of three blue, five red and eight yellow, they gave the perfect balance recommended by Field. To increase the apparent size of the interior, different structural elements were coloured separately - curved members coloured yellow, lattice girders blue, and joists of the glass roof picked out in red. (The choice seems to follow Field's tri-unity of forms, of arc, angle, and line.) A strip of white separated different colours, to avoid the effects of simultaneous contrast. The final effect was enchanting; at close range, the colours were vivid but seen over the 1850-foot length of the building they optically merged into a shimmering, Turneresque grey.

Field claimed to illuminate a truth the ancient Greeks had only dimly perceived - colours were all compounded of light and dark. His own theory was the only correct one: Goethe's somewhat similar investigations would lead to confusion and error, while Newton had used false analogies, to bind colours together in rays of light. Field eschewed new-fangled theories of light waves, and found the choice of red, green and blue, as light's primaries, to be a perverse ingenuity. He was more appreciative of the new science of electrochemistry and, to his credit, was among the first to guess that vision was a photochemical process (although his description was entirely fanciful). Like some other chemists of his day, Field gave light positive and negative charges, and believed that light, electricity, and magnetism were single manifestations of a unified force within nature. Where Field turned these broad analogies to aesthetic ends, others employed them in the service of science. The brilliant experimenter, Michael Faraday, was able to demonstrate a connection between light and magnetism in 1845, the same year a second edition of Field's "Chromatics" was published. Faraday also exploited the forces between magnets and electric currents, enough to make a dynamo. As a result, the second half of the 19th century saw James Clerk Maxwell unite light, electricity, and magnetism by mathematical equations, within an electromagnetic field. And, by the end of the century, A W Rimington was able to harness a massive 150 amps of electric current, to power his colour organ.