FAMOUS CROATS 2007 - ANDRIJA MOHOROVIČIĆ (1857 – 1936)

ANDRIJA MOHOROVIČIĆ (1857 – 1936) Andrija Mohorovičić was born in Volosko near Opatija. In 1875 he enrolled the study of mathematics and physics in Prague. After graduating he taught at grammar schools in Zagreb and Osijek and at the Nautical School in Bakar. In 1892 he was appointed director of the Meteorological Observatory on Grič. In 1893 he was awarded the doctorate of philosophy at the Zagreb University. In 1910 he became titular associate university professor and taught subjects from the area of geophysics and astronomy at the Faculty of Philosophy in Zagreb. In 1893 he was first made associate member and in 1898 full member of the Academy, then the Yugoslav Academy of Sciences and Arts. He retired in the year 1921. At the beginning of his scientific work Andrija Mohorovičić became interested in meteorology and started working in this area. He directed his work into three areas – scientific explanation of specific meteorological phenomena, conducting the complete meteorological service of Croatia and Slavonia of that time and the spreading of the activities of the observatory onto other areas of geophysics, particularly on seismology. Out of the number of his meteorological works what should be particularly pointed out are his observations of clouds, the tornado near Novska and Čazma as well as observations of the climate of Zagreb. At the turn of the 19th into the 20th century Mohorović’s scientific interest focused almost exclusively on problems of seismology, the area where he achieved world-wide recognition and fame. By the analysis of the earthquake in Pokupsko that took place on 8 October 1909, Mohorovičić particularly upgraded perceptions about the mechanisms of spreading (elastic) seismic waves of nearer earthquakes through the Earth’s interior. On this occasion he was the first in the world who, on the basis of the analysis of a seismogram, established the existence of the surface of velocity discontinuity of seismic waves that separate the crust of the Earth from its mantle. This surface of velocity was named Mohorovičić Discontinuity in his honour and its existence was soon confirmed on the whole Earth. This discovery is doubtlessly the most important scientific perception ever published in a Croatian journal. In the procedure of discovering discontinuity Mohorovičić predicted that the velocity of seismic waves in the Earth’s crust gradually increases as waves enter greater depth. He expressed this hypothesis with an exponential function later named Mohorovičić’s law which is nowadays still applied. Mohorovičić equipped the Zagreb seismologic service at the beginning of the 20th century with the most recent seismographs which resulted in raising it to the level of the best equipped observatories in the world. By the acquisition of precise observatory clocks Mohorovičić established the Service of Exact Time in Croatia. The general distinctive feature of Andrija Mohorovičić’s work is his critical attitude to work. He preferred to link his observations to theory but, on the other hand, never positioned theory before observation. His thoughts and ideas were truly visionary and came to be acknowledged many years later (the influence of the earthquake on the buildings’ behaviour, exploitation of the energy of north-eastern winds, models of the Earth and the atmosphere, deep-focus earthquakes, defence against hailstorms...). In 1970, in honour of Mohorovičić, the crater with the diameter of 77 km on the dark side of the Moon was named after him. In 1996 the same happened with the asteroid No. 8422. In recent times his name is used for the discontinuity between the crust and mantle on the planet Mars. The Department of Geophysics, Faculty of Science, University of Zagreb also bears his name and so do the gymnasium in Rijeka, the elementary school in Matulji and several streets in Croatian towns and cities. On the chain worn by the Rector of the University of Zagreb there is also the medallion with Mohorovičić’s image. Andrija Mohorovičić belongs among the most eminent Croatian scientists of all times, and the world geophysicists unquestionably classify him among the outstanding great men of seismology of the 20th century.