Fig. 1. Building of the observatory.

Geomagnetic Observatory of the Geophysical Institute of the Slovak Academy of Sciences is nowadays a modern institution for monitoring and interpretation of the variable Earth's magnetic field. The Observatory founded by Miklós Konkoly-Thege, the landlord and scholar of his time, has exercised not easy development during its 100-year history and nowadays belongs to the world-wide network of geomagnetic observatories.

Miklós Konkoly-Thege (1842–1916) started astronomical observations at Ógyalla (Stará Ďala 1918-1938, Hurbanovo from 1948) in 1871 (Druga, 1992, 1998). It was his great merit that here a complex observatory has gradually been built.

The first sporadic geomagnetic observa­tions at the Ógyalla Observatory are as early as 1867–1871. Gradually, the successive ef­forts to get new instruments and to improve observations have prepared the basis to start regular measurements here.

As the Director of the State Institute for Meteorology and Earth Magnetism in Budapest during 1890–1900, Konkoly-Thege revealed that the geomagnetic measurements in the Buda Observatory have become less reliable due to gradually increasing disturbances because of the growth of the city and its industrialisation. The need to move obser­vations was more and more urgent. After 1890, the Ógyalla measurements, for which the un­favourable industrial influences were negligi­ble, have substituted observational activities of the Buda Observatory. On September 30, 1900 the Geomagnetic Observatory at Ógyalla was officially opened and, according to the Konkoly-Thege's decision, transferred to the state administration. He managed this intention of him to come true only due to his activities as a deputy of the Hungarian Chamber. Earlier he was unsuccessful to transfer the administration of the observatory to the institution capable to arrange its activities financially, namely the Bratislava University (1876) and Budapest University (1880). The new building of the observatory built at that time was mainly for administrative activities, the meteoro­logical instruments being installed in the steeple.

To run the GMF measurements variation hut was built as early as 1898 (Fig. 2.) and the little wooden hut for absolute measurements (Fig. 3.).

Fig. 2. The old variation house.

Fig. 3. The old absolute house.

The results of observations were published (till 1905 the values at 7.00, 14.00 and 21.00 hr only, and then the values for each hour) as monthly reports on all the kinds of observations at the Ógyalla Observatory (1893–1896) and also as annual reports (special editions) of the State Institute for Meteorology and Earth Magnetism in Bu­dapest (1897–1917).

After the World War I and the foundation of Czechoslovak Republic in 1918 the observatory was in responsibility of Ministry of Education and National Enlightment in Prague. A. Dittrich was approved to carry out meas­urements and those were restarted in 1924, namely for D. Since 1938 J. Bouška had started his activities at the observatory. A new field magnetic theodolite Askania for measure­ments of D was installed here by colleagues from the State Institute of Geophysics, Prague. The measurements of H were also started. To measure H variations the Mascart bifilar variometer was installed.

The results of D measurements were published by State Institute of Geophysics in Prague as a periodical "Bulletin magnetique".

After the First Vienna arbitration in November 1938 up to 1945, some southern parts of Slovakia (including Stará Ďala) had been again under Hungary administra­tion. In 1939–1944 G. Barta and J. Bucsy performed observations. In 1939 magnetic devices were reconstructed. The Danish geomagnetician La Cour, who visited the observatory that time, had significantly participated on the reconstruction. He brought three QMH devices, which made it possible to determine Wild theodolite parameters, re­paired in Niemegk (1942). New devices were obtained: La Cour bal­ance, Askania Earth in­ductor with microgalvanometer, Askania Tor­sion Box for D measurements. The publication of the results of observations was renewed in the form of annual reports of the State Institute for Meteorology and Earth Magnet­ism (1939–1944).

After the end of the World War II in 1945 and returning of the territory with Stará Ďala to Czechoslovakia, the modern history of the Hurbanovo GO starts. Its initial phase was most difficult since it was necessary to overcome the problems of restarting of measurements after the late 1944 when all the instruments but variometers were removed to Budapest.

In Slovakia both the new power structure and state administration arise. The Council for Education, Science and Culture established took credentials for admini­stration of the ob­servatory. Štefan Ochaba was appointed as a head of the observa­tory and he was in charge till 1960.

New perspectives for the development of science in Slovakia have opened due to establishment of the supreme scientific institution – Slovak Academy of Sciences (SAS). Its offi­cial foundation on June 18, 1953 has initiated the proc­ess of integra­tion of the existed institutions for scientific research as the unified scientific insti­tutes within the frame of SAS. Academy took the responsibility for the Hurbanovo Geomagnetic Observatory activi­ties. That has soon become a part of the just estab­lished (1954) Geophysical Institute SAS (GPI SAS).

Development of observational devices and maintenance of continuity of measure­ments were from the very beginning considered by the GPI SAS as the most impor­tant.

Š. Ochaba as the first head has already paid much attention to improve the observational base. The same approach was exercised by other officials-in-charge:

Eduard Csitneki 1960–1965

Silvester Krajčovič 1965–1970

Štefan Pintér 1970–1986

Jozef Podsklan 1986–1988

Ján Kiss 1988–1990

Zoltán Vörös 1990–2001

Fridrich Valach 2001–since

In 1948 the observatory gained the Earth inductor and astatic galvanometer of the Mating-Wiesenberg production. The Askania field theodolite was moved from the State Geophysical Institute, Prague. During 1948 the devices on registration of D, H, Z geomagnetic elements have been recon­structed and installed in the variation hut. Registrations of D and H were carried out by two modified single-fibre Carpentier variometers and Z component was measured by means of the La Cour balance.

The utilization of the Helm­holtz coils in each instrument has made it pos­sible to control their sensitivity.

The continuous and complete measurements were started on January 1, 1949 and since that time the complete observational series of the D, H, Z components has been archived.

The D and H measurements carried out by the Askania field theodolite were modernised. Since 1955 a normal Mating-Wiesenberg magnetic theodolite has been used for the D and H measurements. It was in service as standard observa­tional instrument for measurements of D for the more than 40 years. To keep the continuity of measurements the simultaneous measurements by both of instruments mentioned were performed in 1955–1956.

A new hut was built (1950) for absolute measurements (Fig.4.) since the original absolute hut has become old.

Fig. 4. The large absolute house.

In the new absolute hut of 5 x 4 m², there are six pillars to place instruments. The absolute measurements in this hut started in 1951.

In 1958 a new Mating-Wiesenberg variation device with the registration speeds of 2, 6 and 12 cm/h was bought and installed in 1959 after a greater reconstruction of the variation hut (Fig. 5.).

Fig. 5. The new variation house.

It has been used for registration of declination D, H, Z components as long as till 1968 when a combined registration device (with the Mat­ing-Wiesenberg registrator and Bobrov sensors) was installed in the new variation hut. It was used for the H, D, Z and F registration with the registration speeds of 2 and 6 cm/h till 1996. The another variation device of the La Cour type with a quick registration was installed in 1964. Later, in 1969 the Carpentier variation device was substituted by a portable Bobrov type device constructed within the IZMIRAN (Mo­skva) facilities. The scientific cooperation with the IZMIRAN (Institute for the Earth Magnetism, Ionosphere and Radio Wave Propagation of the Academy of Sciences, USSR) was very helpful for modernisation of the GMF registration.

To measure the GMF vertical com­ponent the BMZ (balance magnetometrique zero) instrument No. 243 has been used since 1960. Then (1966–1967) the more sophisticated instruments were supplemented, namely BMZ Nos 273 and 282. At that time the new instruments for the horizontal component measurements were ob­tained, namely QHM 640, 641, 642 and then QHM 1049, 1050 and 1051.

In 1973 the proton magnetometer ELSEC 520/480 with complete equipment was added to the observatory observational devices. Due to Helmholtz coils this instrument made it possible to measure not only the total field, but also both the horizontal and vertical components.

Until the mid-eighties the observatory devices has been running without any changes. The continues registration of variations and the absolute measurements of the GMF were carried out by the instruments as in the sixties. In 1981–1986 the first digital registrations were tested by means of the digital station CMVS-2.

Gradually the change of analogue registrations by digital ones was started. In 1986 a digital proton magnetometer ELSEC 820 M2 was bought. This instrument is the observatory standard for H and Z components nowadays. The measurements of declination D were also improved due to quartz declinometers QD Nos 20 and 21.

The modern digital devices were installed in the observatory within the frame of close international cooperation (1996):

- variation station Torsion Photoelectric Magnetometer TPM (from Poland), which is the modernised quartz Bobrov type variometer

- Magson digital station (from Germany, Volkswagenstiftung).

Both devices are for registration of X, Y, Z components. Later on the GMF analogue photoregistration was completely stopped (1998).

The absolute measurements were also modernised, when the observatory gained (1996) the DI-flux magnetometer (THEO 15B + ELSEC 810) from the Niemegk GO. In 2003 was purchased the another DI-flux magnetometer LEMI-2003.

The favourable conditions for publication activities due to the strategy of the SAV make it possible to publish the results of geomagnetic observations (Results of Geo­magnetic Observations at the Hurbanovo Geomagnetic Observatory, 19xx) in the form of yearbooks. Today the data acquisition on electronical media is used to more extent.

In 1998 our Observatory was officially connected to international program INTERMAGNET – net for the real time working geomagnetic observatories. The status IMO (Intermagnet Magnetic Observatory) was given to it.

Observatory serves as a calibration place for all field magnetometers in Slovakia. It provides information about the state of GMP for the army, for the telecommunications and for some private subjects. It is the reference centre of the measurement of geomagnetic declination in Slovakia.