enabled him to obtain very precise results. From 1875 to 1879, he examined numerous salt solutions, acids and solutions of other materials. His efforts resulted in the law of the independent migration of ions, that is, each type of migrating ion has a specific limiting molar conductivity no matter what combination of ions are in solution, and therefore that a solution's electrical resistance is due only to the migrating ions of a given substances. Kohlrausch showed for weak (incompletely dissociated) electrolytes that the more dilute a solution, the greater its molar conductivity due to increased ionic dissociation. Measuring techniques and instruments During 1895 he succeeded Hermann von Helmholtz as President of the Physikalisch-Technische Reichsanstalt (PTR – Imperial Physical Technical Institute), an office which he held until 1905. Here, as in the past, his activities were focused on experimental and instrumental physics: he constructed instruments and devised new measuring techniques to examine electrolytic conduction in solutions. He concluded the setup of the PTR, a task which had not yet been completed on the death of its first president. He introduced fixed regulations, work schedules and working hours for the Institute. Under direction of Kohlrausch, the PTR created numerous standards and calibration standards which were also used internationally outside Germany. Kohlrausch was intent on creating optimum working conditions in the laboratories and to shield the labs from unwanted external influences. For six years, for instance, he fought against a streetcar line which was due to be laid near the PTR. However, before the streetcar was to make its first journey, the institute succeeded in developing an astatic torsion magnetometer which was uninfluenced by disturbing electromagnetic fields. The use of this instrument and the shielded wire galvanometer developed by du Bois and Rubens meant that precision electrical and magnetic work continued to be possible. Over the years, Kohlrausch added experiments which met the needs of physical chemistry and electrical technology in particular. He improved precision measuring instruments and developed numerous measuring methods in almost all of the fields of physics known during his lifetime, including a reflectivity meter, a tangent galvanometer, and various types of magnetometers and dynamometers. The Kohlrausch bridge, which he invented at that time for the purpose of measuring conductivity, is still well known today. Like Helmholtz and Siemens, Kohlrausch also saw the possibilities inherent in applied and basic research in the natural sciences and technology. He lay the foundations