Andrija Mohorovičić (January 23, 1857 - December 18, 1936) was a noted meteorologist and seismologist.

Early years

Born in the village Volosko, near Opatija, in Istria, Croatia, he obtained the elementary education there and continued study in the gymnasium in Rijeka. At the age of 15, Mohorovičić knew Italian, English and German, Latin and Ancient Greek. His higher education was in mathematics and physics at the Faculty of Philosophy in Prague (Praha or Prag) in 1875 where one of his professors was the physicist Ernst Mach.

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 Yugoslav Academy of Sciences and Arts in Zagreb where he was private docent, and in 1910 he became titular associate university professor.

Meteorology

In Bakar he first came in touch with meteorology, which he taught at Royal Nautical School. The very science influenced him in that extend 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. On 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, establishing a service for all of Croatia, while simultaneously teaching geophysics and astronomy at the university.

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 it 30 m away. 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 gained him his degree as doctor of philosophy in 1893.

Interests and ideas

In March of 1892 Mohorovičić began the astronomical observation of stars passing through the Grič meridian to establish the precise time. At the beginning of April, 1893, he established a network of stations to follow thunderstorm s, and in 1899 he founded hail_defence stations in the Jaska (Jastrebarsko) region. In 1899, he started a project for research into and harnessing of the energy of the northern wind bura (bora) in the karst region. In 1901, he was appointed head of the complete meteorological service of Croatia and Slavonia, and his efforts raised the quality of personnel and the equipment to the European level. He gradually extended the activities of the observatory toward geophysics, seismology, geomagnetism and gravity, switching his main interest towards seismology.

Seismology

On October 8, 1909, 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 first in the world to establish, (based seismic waves), surface and velocity discontinuity that separates the crust of the planet Earth from the mantle. There are depths where seismic waves do change speed and also there is change in chemical composition. 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 Moho.

Afterward, the scientists confirmed the existence of this discontinuity under all the continents and oceans. Mohorovičić's thoughts and ideas were visionary and truly understood many years later (an earthquake's effects on the buildings, deep-focus earthquakes, locating earthquake epicenters, the Earth models, seismographs, harnessing the energy of the wind, hail defence).

He retired in 1921. Mohorovičić is one of the most prominent earth scientists in 20th century. In the year 1970, a Moon crater (77 km in diameter) on its dark side was named in his honor. In 1996, an Asteroid 8422 with a period of 5 years and 38 days was also named after him—Mohorovičić.

External links

• Prominent Istrians _ Andrija Mohorovicic (http://www.istrians.com/istria/illustri/mohorovicic/)
• Croatian Geophysical Society _ in Croatian (http://www.gfz.hr/rad.php)
• Andrija Mohorovičić (1857_1936) at the Croatian Giants of Science _ in Croatian (http://jagor.srce.hr/zuh/velikani/mohorovk.htm)