magnetic radiation varies inversely to the fourth power of the wavelength. This dispersion or scat- tering is referred to as Rayleigh scattering, after Lord Rayleigh, who in 1871 published a paper that described this phenomenon. Rayleigh scattering explains the blue color of the sunlit sky, since blue light, which is locat- ed at the short-wavelength portion of the visible spectrum, will be scat- tered more strongly than longer wavelengths, such as green, yellow, orange, and red. Thus, when we view the sky in a direction other than toward the sun, we observe scattered light, which appears blue. Mathe- matically we can denote the Rayleigh effect as 1/X4. As an example of the Rayleigh effect, scattering at 400 nm becomes 9.4 times as great as that 700 nm when a person views a common location. Thus, if we plot attenuation as a function of wavelength and consider the effect of Rayleigh scattering only, the relationship would appear as shown in the top portion of Figure 3.10. If we consider only the Rayleigh effect, we would always want to operate at a relatively long wavelength to minimize attenuation. However, another important characteristic of light that we need to consider is its absorption. Absorption is caused by resid- ual impurities in the fiber. In addition, it is nonlinear, with absorption higher at some wavelengths than others. This is shown in the middle por- tion of Figure 3.10. In case you are wondering about the bump in the degree of attenua- tion beginning at 1350 nm, that increase results from the effect of light between 1350 and 1450 nm in the presence of hydroxyl radicals in the cable material. In some publications you will note the term OH absorption at the top of the peak at approximately 1400 nm to denote the effect of hydroxyl radicals. Thus, the actual attenuation spectrum as a function of wavelength is a complex process. When we consider both the Rayleigh effect and absorption, the plot of attenuation versus wavelength appears as shown in the lower portion of Figure 3.10. If you focus on the 