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The Rainbow Bridge: Rainbows in Art, Myth, and Science.

2002; Lippincott Williams & Wilkins; Volume: 79; Issue: 4 Linguagem: Inglês

10.1097/00006324-200204000-00007

1538-9235

Michael C. Barris,

Maritime and Coastal Archaeology

The Rainbow Bridge: Rainbows in Art, Myth, and Science. Raymond L. Lee, Jr. and Alistair B. Fraser. University Park, PA: Pennsylvania State University Press, 2001. Pages: 393. Price: $65.00. ISBN 0-271-01977-8. “The rainbow is a bridge between the two cultures: poets and scientists alike have long been challenged to describe it.”1 Meteorologists and authors Lee and Fraser present the rainbow not only as a bridge between disciplinary cultures but as a bridge between all the continents and all peoples. Their index entry for “peoples” includes 53 names ranging from “Abnaki” to “Zulu.” They find evidence for artifacts of rainbow symbolism even among the ancient Egyptians, residents of a country where archaeological evidence suggests rainfall was once more common than now (pp. 12–14). Their documentation of artifacts ranges across 10 millennia. FIGUREFigureThe Rainbow Bridge has 10 chapters, chronologically arranged from earliest times to most recent. The first chapter presents pre-Christian artifacts; the second chapter, Christian artifacts; and the third chapter, secular artifacts. The remaining chapters deal with the optical history of rainbows, with the exception of the seventh chapter, which tackles color science, and the last chapter, which tackles advertising logos. The book concludes with a brief appendix, a field guide for rainbow chasers. Lee and Fraser have produced an unusual book with universal appeal to all sighted humans, from preliterate five-year-olds to hyperliterate scholars. The preliterate will respond to the arrangement of 96 color plates ranging broadly from the Great Masters to cartoons; the 64 black-and-white plates have a lesser impact. Many art books have all of the color plates clustered together. Lee and Fraser have programmed their color plates as if they were a fireworks display. The color plates are spaced by text, so that rarely does one see more than one color plate at a time when the book is opened. Proceeding rapidly through the book at a constant rate, one hears the synesthetic thud of pyrotechnic mortars getting steadily louder as one saturated rainbow image follows another. Finally, in the last chapter, there is a sudden popping of many small mortars as many small images of good humor are grouped together on single pages. Then there is a deep mortar thud, followed by a final one only slightly less deep. My reaction to this display is “Wow.” The hyperliterate will respond to the Greek (Fig. 2-1) and Japanese (Fig. 3-2) calligraphy, the 565 references and 1,947 footnotes, and the trigonometry and chromaticity diagrams of the optics chapters. For those with status between these two extremes, there are ladies’ fashion (Fig. 2-8), ships (Figs. 2-7 and 8-24), airplanes (Fig. 8-10), and animals (Figs. 2-7 and 7-1). The prudish parent may need to be warned about unclothed human figures in nine images; others will want to acquire the book for that purpose. There are two images of horror. The core of the book is two remarkable photographs taken within minutes of each other, apparently, by author Fraser in 1973. Fig. 7-20 shows the left ends of a double rainbow. One appreciates the transparency of the phenomenon; there is no pot of gold (Fig. 9-1) at the end of the photographed rainbow. Fig. 8-5 presents the full arc of a primary rainbow. The photographer-reader will want to know how Fraser accomplished this feat. On a sunny day in July 1982, I assisted an artist in the construction of a photomontage of a primary rainbow recorded in the mist of Niagara Falls. No single photograph taken with a 35 mm camera captured more than half of the arc. Photographer Jeff Gnass 2 captured three-quarters of an arc using a medium-format camera. I think that a large-format camera is needed to capture an entire arc. “Optically, the rainbow is just a distorted image of the sun, ” reports Lee and Fraser (p. 321). This definition will trouble the optometrist schooled in entoptic phenomena. This is a concept prominently articulated in 1932 3 that has not escaped into general culture from the eye care clinic. On an early sunny morning or late afternoon, one can observe the entoptic nature of rainbows with a high-water spray, say, from a fountain or a lawn sprinkler (p. 221). Stand with your back to the sun (Fig. 8-5). Observe the visual spectrum with red being outermost and violet innermost. As you start to walk around the spray, the spectrum will disappear, only to reappear when you complete your circuit. The rainbow is not an object. “Aristotle recognized that the bow’s center lies on the straight line connecting the observer’s eye and the sun” (p. 134). “When the Rainbow appears at Noon [in England], the height of the sun at that hour of the day causes but a small segment of the circle to be seen, and this gives the Bow its low or flat appearance: the Noonday-bow is therefore best seen ‘Smiling in a Winter’s day, ’ as in the Summer, after the sun has passed a certain altitude, a Rainbow cannot appear: it must be observed that a Rainbow can never appear foreshortened, or be seen obliquely, as it must be parallel with the plane of the picture, though a part of it only may be introduced; nor can a Rainbow be seen through any intervening cloud, however small or thin, as the reflected rays are dispersed by it, and are thus prevented from reaching the eye; consequently the Bow is imperfect in that part” (p. 84, quoting the painter John Constable’s writings of 1833). “Bacon states that the rainbow’s summit can appear no higher than 42° above the horizon, and then only at sunrise or sunset (assuming level ground)…. He perceptively noted that more than a semicircle will be visible in rainbows seen ‘on a high mountain or on a lofty tower [or on the edge of a gorge]’” (p. 156). Lee and Fraser criticize several painters at length for their misrepresentations of the entoptic phenomena of the rainbow. The most frequent criticisms are depictions of impossible oblique orientations, rainbow orientation inconsistent with object shadows, misordered colors in the spectra, and impossible arc sizes in famous landscapes that can be photographed for comparison now and in the future. Well-known depictions of rainbows by John Constable (Fig. 3-4), John Everett Millais (Fig. 3-5), Frederic Edwin Church (Figs. 3-6 and 3-7), Georges Seurat (Fig. 7-17), and J.M.W. Turner (Figs. 8-24, 8-25, and 8-26) are reproduced, among others. However, Lee and Fraser’s catalogue of rainbow painting is not exhaustive: I favor paintings by Wassily Kandinsky, 4 Friedensreich Hundertwasser, 5 Louis Remy Mignot, 6 William Blake, 7 Paul Signac, 8 and Claude Monet, 9 not presented here. In 1637, Rene Descartes gave us our current understanding of rainbow optics (Fig. 6-4), namely, the primary rainbow is produced in a single spherical water drop by a refraction, a reflection, and a second refraction. As spherical water drops fall from a cloud, the primary rainbow is appreciated from this optical sequence in a great number of raindrops. The spectrum of the rainbow becomes more saturated as drop radius increases from 0.01 to 1.0 mm (Fig. 8-11). Descartes’ frequently reproduced figure (Fig. 6-4) depicts a parabolic rainbow at an impossible oblique orientation, which nevertheless represents an appropriate orientation for the depicted observer. Descartes’ calculations model the rainbow as an arc. That is, the rainbow has a constant radius. Nevertheless, in his painting entitled “The Jetty at Le Havre,” the impressionistic painter Claude Monet 9 depicts a parabolic half of a primary rainbow. Monet was committed to depiction of sense data stripped of visual constancies. 10 In Miami, Florida, at 7:30 am Eastern Daylight Savings Time on August 24, 1999, I observed half of a persistent and deeply-saturated double rainbow. “The time and location of the rainbows … specify the sun’s elevation; which in turn lets us estimate sunlight’s spectrum.” (p. 238) Both the primary and secondary bow appeared to be parabolic. The upper part of the secondary bow appeared to be in a closer plane than the primary bow, although the lower part of the secondary bow appeared to be in the same plane as the primary bow. If these bows were objects rather than entoptic phenomena, this perception would be impossible as there was no apparent transition range between the upper and lower planes, even upon persistent scanning of the secondary bow. I had no photographic camera at hand, but I was able to record some relative measures in the same frontoparallel plane using extended thumb and index finger as a caliper in one case and distance between knuckle joints as a second caliper. Fixing my thumb at the antisolar point (the optical center of the rainbow, Fig. A-1), I was able to confirm that all radii of the primary bow were equal, confirming a physical arc in wild disagreement with my perception of a parabola. I was further able to confirm that all radii between the primary and secondary bows were equal. Photographs invariably record rainbows as arcs. My perception of that double rainbow resembled my recollected perceptions of earlier visits to the intimidating interiors of the Romanesque cathedrals of Norwich, England, and Chartres, France. This gives insight into literary references to the vault of heaven (“De arcu coelesti,” p. 37; p. 139; p. 327, note 41; and Fig. 4-1). At 5:25 pm Eastern Daylight Savings Time on October 8, 1999, I perceived an intermittent and unsaturated double rainbow in the same location in Miami. This unsaturated rainbow appeared arcuate in both the primary and secondary bows. Atsuki Higashiyama 11 provides psychophysical evidence for lengthened judgments of verticals relative to horizontals and applies his analysis to “the horizontal-vertical illusion, overconstancy of size, and the moon illusion.” I extend his analysis to my parabolic perception of the rainbow on August 24, 1999. Lee and Fraser come close to making this conclusion in their analysis of Fig. 8-10, but they do not quite get there. However, they do succeed in their goal to “inspire readers to look at the rainbow anew.”