1. This special issue of “Geofizika” marks the 125th anniversary of the Zagreb - Grič meteorological observatory, which was officially named the Geophysical Institute in 1921, after its activities had become widely spread. For about 80 years the Geophysical Institute has been the only institution maintaining its interest in geophysics in Croatia; it has also existed as an autonomous educational facility within the Faculty of Science for the last 40 years, producing generations of trained geophysicians and so covering the needs of the Socialist Republic of Croatia and partly meeting the occupational demands of the whole country.
2. To trace the origins of the Geophysical Institute one should go back to the meteorological station founded in Zagreb on 1st December 1861 as a part of a secondary-school physical laboratory. In the directorship of Ivan Stožir, the physics teacher, the meteorological station developed from 1861 to 1891 into a meteorological observatory with its own publications and with the first seismograph. Within the next 30 years (1892-1921), under Dr Andrija Mohorovičić, a number of significant changes occurred: the observatory turned into an independent institution responsible for the network of meteorological stations in North Croatia; besides the meteorological observatory, a seismological observatory was founded; public time service was updated; geomagnetic measurements of North Croatia were accomplished. The third long-time Head of the Institute was Dr Stjepan Škreb, in whose time the highest standards in meteorological measurements and their processing were set. The Institute attracted a considerable number of research workers whose activities also included physical oceanography. With the Hydrometeorological Service established in 1947, the only meteorological measurements still done by the Geophysical Institute were those on the Grič observatory. In 1951 the Geophysical Institute was amalgamated to the Faculty of Science. After that, the Institute was respectively run by the professors Josip Goldberg, Branko Maksić, Berislav Makjanić and Dragutin Skoko. They all contributed to the booming of geophysics as an academic subject: more prominence was given to seismology, and the Institute outgrew its old building and moved into its new head- quarters on Horvatovac in 1982, with the exception of the meteorological observatory which still remains on Grič.
3. The Faculty of Science was founded in June 1946 with geophysics established as an autonomous academic subject named Geophysics with Meteorology and lectured at the Department of Mathematics and Physics. The present organization of the undergraduate studies stimulates the development of various geophysical disciplines. The first two years of the curriculum consist of courses in mathematics and physics; the third year is devoted to the acquisition of basic knowledge in physics of the atmosphere, the sea and the Earth’s interior. In the final, fourth year students may pursue their training either towards meteorology or seismology and physics of the Earth’s interior. By the end of 1985, the number of graduates in physics majoring in Geophysics with Meteorology amounted to 182. Well qualified to pursue their academic career, these graduates either start a post- graduate study and conduct scientific research or find the daily routine of their jobs as meteorologists, seismologists or physical oceanographers easy to follow. The Geophysical Institute also takes over the organization of the postgraduate course in physics - geophysics at the Faculty of Science. For their future academic vocation, prospective students are free to choose among physics of the atmosphere (started in the academic year 1960-61), physics of the sea (from 1969-70) or physics of the Earth’s interior (from l972-73) Fifteen candidates earned the doctoral degree in physics under the supervision of the Geophysical Institute staff.
4. The scientific work in meteorology primarily comprised the climatic characteristics of the Zagreb area; it was also extended to Croatia, covering the entire region from the Adriatic coast to the Pannonian valley. These works mirrored the general trends in the world climatology, embracing formal researches in periodicity of meteorological time series, climatic factors as defined by Hann, and dynamic climatology which approaches the phenomenon of climate through geographic factors and the general atmospheric circulation. Among many of the Institute’s staff devoted to research into climate, Goldberg deserves to be specially mentioned. Solar radiation energy in Yugoslavia, outside and within the atmosphere, as well as at the ground, comprises the second academic field of interest. Applied research into heliotechnics, agriculture, medical meteorology and ecology was carried out. General subjects were covered primarily by Škreb’s works published in “Meteorologische Zeitschrift” between the two world wars. These works clarified some notions related to meteorological observations and to the application of some statistical methods to climatology. Besides, Makjanić’s models of air flow over mountains are worth mentioning.
‘Mohorovičić gave a major scientific contribution to seismology by proving the existence of a discontinuity surface, i.e. the boundary between the Earth’s crust and mantle. He proved that by studying seismic waves, one could get to know more about the Earth’s layer-like structure. He also showed that near and distant earthquakes can be studied separately, and theoretically anticipated the seismogram of deep focal earthquakes. Moreover, Mohorovičić devised the general travel time curves for the Pn and Sn, waves, which were later to be used by Macelwane, Gutenberg and Richter as the basis for their travel - time curves of all the waves spreading through the Earth’s interior. Josip Mokrović devised the travel-time curves for the Zagreb area including all the phases of body seismic waves for earthquakes of normal depths; they are used in the analysis of the Zagreb seismograms. Furthermore, a number of methods for locating epicentres, i.e. for determining the basic kinematic parameters of earthquakes, have been developed since Mohorovičić. Papers dealing with the optimum distribution of seismological stations according to the Monte Carlo method are referred to in the international seismological literature. Makjanić’s works, inspired by the theory of extremes, contribute to the statistical analysis of earthquakes. In his works particular importance is given to the pro position of the general exponential distribution of intensity or magnitudes of earthquakes, which makes the well-known Gutenberg-Richter’s relation a special case. Studies in seismicity, seismotectonic processes and seismic zoning of Croatia and Yugoslavia were developed. Works dealing with analytical definitions of the estimation models of the possible maximum earthquake magnitude based on the given geologic and neotectonic parameters are also worth mentioning. Finally, let us mention the theoretical and empirical research in Love’s and Rayleigh’s surface waves of earthquakes.
The research in marine physics was primarily concentrated on the Adriatic Sea, particularly its mean sea level, seiches, tides, response to the atmospheric forcing, and, recently, winds driven currents. Goldberg’s variant of the method of residue in the research of seiches was internationally recognized, as was the study of the Adriatic Sea seiches by Marijan Kasumović.
Presenting the mathematical solution to the problem of three or more bodies, Radovan Vernić gave a major scientific contribution to astronomy.
The spatial division of the elements of the Earth’s magnetism resulted from geomagnetic research in Croatia; temporal changes were followed and the spatial anomalies of declination were explained. In addition, few papers dealing with atmospheric electricity, gravity and the shape of the Earth were published.
5. Besides scientific papers and university textbooks, the Institute members produced a bulk of various technical, popular, historical or occasional publications.
6. The collaboration of the Geophysical Institute with institutions abroad is carried out through the exchange of publications and the regular exchange of meteorological, seismological and tide-gauge data. Furthermore, its staff participates in international geophysical meetings and derives benefit from research scholarships. They also actively participate in international research commissions and in international scientific research projects.
7. The Institute encourages the collaboration with Yugoslav scientific institutions.
8. Providing scientific support to Yugoslav economy, the Geophysical Institute has conducted numerous geophysical expertises, most often dealing with construction problems in seismically active areas.
9. Many of the Geophysical Institute staff was teachers of mathematics and physics. Some of them were authors of secondary-school physics and astronomy textbooks, and published articles in popular science magazines for secondary-school teachers and pupils.
10. Seven of the Geophysical Institute staff was elected to the Yugoslav Academy of Arts and Sciences, which should be considered as recognition of their scientific work.
11. Having made various contributions to science, some of the Institute members received public recognitions. Named after its founder, the boundary between the Earth’s crust and mantle is called the Mohorovičić discontinuity, and the analytical expression of the velocity increase of the seismic wave “with the depth is called Mohorovičić’s law. In 1970, the General Assembly of the International Astronomic Society paid tribute to Mohorovičić by calling one of the Moon’s craters by his name.