Andrija Mohorovičić

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Andrija Mohorovičić (c. 1880).
Andrija Mohorovičić (c. 1880).

Andrija Mohorovičić (pronounced [ˈandrija mɔhɔːrɔvitʃiʨ]) (January 23, 1857 – December 18, 1936) was a notable Croatian meteorologist and seismologist. He is best known as the eponym for the Mohorovičić discontinuity.

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[edit] Early years

Mohorovičić was born in Volosko near Opatija, where his father, also named Andrija, was a blacksmith making anchors. The younger Andrija himself loved the sea and he married a captain's daughter, Silvija Verni. Together, they had four sons.

Andrija Jr. obtained his elementary education in his home town, continued his study in the gymnasium of a neighboring town, Rijeka, and received his higher education in mathematics and physics at the Faculty of Philosophy in Prague in 1875. There, one of his professors was the famous physicist Ernst Mach. At the age of 15 the junior Mohorovičić knew Italian, English and French and later he learned German, Latin and Ancient Greek.

[edit] Education career

His career began with a teaching post in the Zagreb gymnasium (1879 -1880) and then secondary school in Osijek. In 1882, he began to teach at the Royal Nautical School in Bakar, near Rijeka, where he remained for nine years. Works initiated or done there were crucial for the beginning of Mohorovičić's scientific work. From 1893, when he became a corresponding member, to 1917-18 he taught subjects in the fields of geophysics and astronomy at the Faculty of Philosophy, University of Zagreb. In 1898 he became a full member of what was then the Croatian Academy of Sciences and Arts in Zagreb where he was private docent, and in 1910 he became titular associate university professor.

[edit] Meteorology

In Bakar he first came in touch with meteorology, which he taught at Royal Nautical School. The science influenced him to the extent that he founded the local meteorological station in 1887. He started making systematic observations, measurements, analyses, inventing and constructing instruments to measure both horizontal and vertical velocity of clouds. In 1907, he wrote Instructions for the Observation of Precipitation in Croatia and Slavonia. At his own request in 1891, he was transferred to the secondary school in Zagreb where, in 1892, he became the head of the Meteorological Observatory in Grič, established a service for all of Croatia, while simultaneously teaching geophysics and astronomy at the university.

One extraordinary meteorological phenomenon that he observed was the tornado in Novska on March 31, 1892 which picked up a 13 t railway carriage with 50 passengers and threw a distance of 30 m. He also observed the "vijor" (whirlwind) near Čazma in 1898 and studied the climate in the capital Zagreb. In his last paper on meteorology in 1901, he discussed the decrease in atmospheric temperature with height. The accumulated data of his observations of clouds formed the basis for his doctoral thesis On the Observation of Clouds, the Daily and Annual Cloud Period in Bakar presented to the University of Zagreb and which earnd him his degree as doctor of philosophy in 1893.

[edit] Seismology

On October 8, 1909, an earthquake struck, with an epicentre in the Pokuplje region 39 km southeast of Zagreb. A number of existing seismographs were installed before and provided invaluable data upon which he made new discoveries. He concluded that when seismic waves strike the boundary between different types of material, they are reflected and refracted, just as light is when striking a prism, and that when earthquakes occur, two waves—longitudinal and transversal—propagate through the soil with different velocities.

By analyzing data received from more observation posts, Mohorovičić concluded that the Earth consists of surface layers above an internal core. He was the first scientist to establish, based on the evidence of seismic wave behaviour, the discontinuity that separates the crust of the planet Earth from the mantle. According to Mohorovičić, a layered structure would explain the observation of depths where seismic waves change speed and the difference in chemical composition between rocks from the crust and those from the mantle. From the data collected he estimated the thickness of the upper layer (crust) to be 54 km. We know today that the crust is 5-9 km deep beneath the ocean floor and 25-60 km beneath the continents carried on tectonic plates. This layer is called the Mohorovičić Discontinuity or, because of the complexity of his name to non-Croatian speakers, Moho.

Subsequent study of the Earth interior confirmed the existence of this discontinuity under all the continents and oceans. Mohorovičić's thoughts and ideas were visionary and were only truly understood many years later from detailed observations of earthquake effects on buildings, deep focus earthquakes, locating earthquake epicenters, Earth models, seismographs, harnessing the energy of the wind, hail defence and other related elements of the geological body of knowledge known as geoscience.

He retired in 1921. Mohorovičić is one of the most prominent earth scientists in 20th century. In the year 1970, Mohorovičić crater (77 km in diameter) on the Moon's far side was named in his honor. In 1996, asteroid 8422 Mohorovičić with a period of 5 years and 38 days was also named after him. A school ship in the Croatian Navy is named after him.

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