The relative variation of attenuation coefficient with wavelength has been studied in the laboratory for distilled water and seawater. The study was for the purpose of locating any very fine structure in the attenuation vs wavelength curve. The spectral region from 3750 A to 6850 A was examined with 0.2 A resolution; water paths were 9.7 m and 19.5 m. Studies of the microphotometer traces show no discernible very fine structure in either distilled water or seawater. The limit of detection was set by plate grain and corresponded to a variation of 0.1 x 10(-4) /cm in the attenuation coefficient. Curves of relative coefficients vs wavelength show very shallow unstructured peaks at about 4700 A, 5150 A, and 5500 A, but these are relatively broad ( approximately 50 A).