in 1917 and was not resumed after the war. The 1917 Annual Report of the committee ended with the unusual note: "Because of the European war the Committee has had much difficulty in the way of correspondence. The German member, Professor Ostwald, has not been heard from in connection with this report. Possibly the censorship of letters, either in Germany or en route, has led to a miscarriage". Scientific measurements As part of Ostwald's investigations in to chemical equilibria, chemical affinity, and acid-base interactions, he recognized that many established analytical methods disturb the chemical systems under investigation. He therefore turned to physical measurements as surrogate methods to understand these important basic phenomena. One such physical measurement is the measurement of the viscosity, or resistance to flow, of a liquid. Ostwald invented a device for this purpose consisting of bulbs that act as reservoirs for a liquid with a capillary, or thin tube, in between the reservoirs. The time that it takes for the liquid to flow through the capillary from one reservoir to the other is an indication of the viscosity of the liquid. Using a reference solution, the viscosity of the liquid can be quantified. Ostwald typically used this device to study the behavior of solutes in water solutions. These devices came to be known as Ostwald viscometers and are in widespread use in contemporary times for research and quality control purposes. Ostwald designed a pipette that could be used to transfer and measure liquids, especially serous fluids. This design was later improved by Otto Folin. This type of pipette has a bulb at the lower end as a particular design feature. It became known as the Ostwald-Folin pipette and is widely used in contemporary times. Color science Following his 1906 retirement from academia, Ostwald became interested in the systematization of colors, which could be useful both scientifically and in the arts. He published The Color Primer and also The Color Atlas during the period of 1916–8. These publications established relationships between the various visual colors. Ostwald represented these as a three dimensional representation of color space that is a topological solid consisting of two cones. One apex of the cone is pure white while the other is pure black. The eight primary colors are represented along the sides of the two cones. In this representation, each color is a mixture of white, black, and the eight primary colors.