The cover illustration is a schematic of the two-sinker densimeter showing four weighings; (a) weighing of the tantalum sinker, (b) weighing of the titanium sinker, (c) weighing of the balance calibration weight, and (d) weighing of the balance tare weight; in (c) and (d) both sinkers are on their rests. See the paper on page 29 in this issue by M. O. McLinden and J. D. Splett for more information. Cover illustration adapted by C. Carey.