in the two limits. We confirmed this experimentally by measuring r s optically for sub-millimetric and millimetric-sized droplets on black Si and Glaco surfaces (Figs. ). When rs is plotted against R in logarithmic scale, we found a slope of 1 and 2 for R < 1 and R > 1, respectively, consistent with predictions from Equa-tion 2 (Fig. ). Dashed-dot line is the best linear fit for rs vs R (using data only for R < 0.1) with sin θ as a fitting parameter; solid line is the expression rs = ! 2/3 R2 with no other fitting parameter.