Some of the best-known scientists related to Estonia include astronomers Friedrich Georg Wilhelm von Struve, Ernst Öpik and Jaan Einasto, biologist Karl Ernst von Baer, Jakob von Uexküll, chemists Wilhelm Ostwald and Carl Schmidt, economist Ragnar Nurkse, mathematician Edgar Krahn, medical researchers Ludvig Puusepp and Nikolay Pirogov, physicist Thomas Johann Seebeck, political scientist Rein Taagepera, psychologist Endel Tulving and Risto Näätänen, semiotician Juri Lotman.