This article presents the most important facts on the life and scientific achievements of Steponas Kolupaila (1892–1964) – one of the most famous hydrologists of the 20th century. This Lithuanian scientist is especially well known for his book Bibliography of Hydrometry.

Historical geographical works typically contain many latitude measurements of locations: all show measurement errors and some of these refer to lost cities. How can we estimate errors? How can we know the right position of lost cities? This work shows a general approach to give a scientific answer to these questions in two particular case studies: Ptolemy's Geography and Riccioli's work on geography.

Friedrich Robert Helmert died in Potsdam in 1917. He was, for over 30 years, director of the Royal Prussian Geodetic Institute and of the Central Bureau of the Internationale Erdmessung, today's IAG. He dedicated his life and his scientific career to the field of geodesy. His teachings on theoretical and physical geodesy were incorporated into university curricula around the world and hence into international endeavours to measure planet Earth.