Information on the cover image
Original figure from Skibitzke and Robinson (1963)
The image on the book cover is based on the above figure from the U.S. Geological Survey Professional Paper 386-B entitled "Dispersion in Ground Water Flowing Through Heterogeneous Materials" by Skibitzke and Robinson (1963). In this pioneering study of the effect of heterogeneity on solute transport, the authors constructed a sand box approximately 4 feet long and 1 foot wide, and embedded narrow bodies of coarse sand in a matrix of fine sand. Two dye tracers (red and green) were injected into the sand box. Skibitzke and Robinson concluded:
"Laboratory studies of dispersion in water flowing through porous media show that the heterogeneity of the medium is the dominant dispersive factor. All other factors have insignificant effects on dispersion."