Iridescences: The Physical Colors of Insects , SergeBerthier , (translated from French by CapucineLafait ), Springer, New York, 2007. $139.00 (160 pp.). ISBN 978-0-387-34119-4

Serge Berthier’s Iridescences: The Physical Colors of Insects is purported to be a “new, improved, and substantially modified version” of his Les couleurs des papillons ou l’mpérative beauté: Propriétés optiques des ailes de papillons, or The Colors of Butterflies or Imperative Beauty: Optical Properties of the Wings of Butterflies (Springer, 2000). Berthier is a professor of physics at the University of Paris Diderot–7 and researches biological structures, colors, and biomimetics at Pierre and Marie Curie University. The one positive aspect of Iridescences, originally published in French in 2003, is that it does have wonderful color photographs that show some amazing detail of the structure and morphology of the orders Coleoptera, which includes beetles, weevils, and fireflies, and Lepidoptera, which includes butterflies and moths.

Berthier’s book could have been a very nice piece of work if it had been proofread to correct the plethora of errors in grammar, history, and references to figures. For example, on page 3 in the first chapter, the author refers to “Lord Raleigh”—yes, with the last name misspelled the same way each time the physicist is mentioned—as fourth baron, who was at Imperial College London, which is correct. However, when most physicists see the name “Lord Rayleigh,” they think of the more famous Rayleigh, John William Strutt, who was third baron and taught at Cambridge University. Berthier is actually referring to Robert J. Strutt, Lord Rayleigh’s eldest son who inherited the title after his father died in 1919.

In chapter 2, Berthier takes readers through plausible arguments about the myriad of color variations found in insects, and in chapters 3 and 4 he focuses on the different characteristic lengths of scales of insect wings in both Coleoptera and Lepidoptera. He then discusses in chapter 5 how pigmentation and structure are responsible for most color variation. He introduces equation 5-1, which shows how to get an interference reflection minimum from a thin layer, yet there is no figure or explanation as to where the equation comes from; unless the reader is already familiar with thin-film interference theory, the equation will mean nothing.

Another repeated annoyance is that the descriptions and labels of figures are written in a mixture of French and English. The labels in figure 11.3 are entirely written in French while the figure caption is written in English. In chapter 13, the author introduces the trichromatic coordinates R, G, B but then in equation 13-3 uses normalized r, ν, b coordinates. One has to assume that the ν stands for “vert,” the French word for “green.” In addition, many of the figures are poorly done. For instance, figure 6.3, which shows the Fresnel reflection coefficient, has no scale for the ordinate. It should also be noted that the Fresnel formulas are not presented until chapter 7. Also, in chapter 6, the author introduces the Kramers–Kronig relations, equation 6-7, that are incorrect as presented.

In chapter 7, “1-Dimensional Structures: Interferences,” Berthier attributes the laws of reflection and refraction to both Willebrord Snel van Royen and René Descartes. However, back in figure 6.2 the law of refraction is called Descartes’ law, and on page 90 in chapter 8, “2-Dimensional Structures: Interferences and Diffraction,” Berthier refers to it as “Snell’s law.” But the law of refraction was actually first discovered by Thomas Harriot in 1602, though that was not known until 1959. Chapter 9, “3-Dimensional Structures: Crystalline Diffraction,” deals with periodicity in three dimensions. Berthier introduces the Bragg relation, equation 9-1, as 2d sinθ = , in which he uses k to represent an integer, another hassle because we are used to seeing k as the wave number. In the sentence above the equation, he refers to Φ as the angle to be used in the equation, which contains θ, not Φ. That equation and the accompanying figure 9.1 give no clue as to why constructive interference occurs. The author then goes on to introduce a two-dimensional Fourier transform in equation 9-2, again with no explanation.

In Chapter 10, “Amorphous Structures: Scattering,” Berthier discusses the concept of larger-size particle scattering within the framework developed by Gustav Mie in 1908. The author later gives credit for the first development to Ludwig Lorenz; however, although Lorenz developed the theory in 1890, he only published his research in Danish. Most people today give credit to both men and refer to the Lorenz–Mie theory. Berthier then ties the theory to the scattering structures found in certain butterflies, which allows readers to understand the insects’ color variation. Chapter 11 treats selective absorption and some of the chemistry necessary to explain it.

I found chapter 12, on thermoregulation and spectral selectivity in butterflies, quite informative; it explained how essential heat transfer is to the survival of those marvelous insects. In the final chapter, 13, “Vision and Colorimetry,” the author uses trichromatic coordinates to explain insect vision. He briefly discusses the perception of polarized light by insects but does not mention the enormous amount of work already published on the subject.

In short, if you are looking for a book that offers some understanding of the relationship between the basic laws of physics and the coloring of insects, Iridescences leaves much to be desired. On the other hand, if you want to see some wonderful photographs that show the intricate and delicate structures of insect wings, then Berthier’s book fits the bill.