"Theories need not be true, only good"
/ Loránd Eötvös /
In his scientific research Eötvös was not interested in those topics that were fashionable
at that time, and would have brought him immediate public acclaim. He was concerned with
capillarity, gravitation and magnetism, phenomena so taken for granted that a superficial
observer would fail to see the mysterious powers at work within them. He formulated his ars
poetica as follows:
"The true natural scientist ... finds pleasure in research itself and in those
results which help to increase the prosperity of mankind."
He was still a university student when he began to concern himself with capillarity under
the guidance of F. Neumann.
His pioneer research discovered a basic physical principle, called
"the Eötvös Rule", and became part of the netural science.
After studying capillarity Eötvös turned his attention to gravitation and magnetism.
From then onwards for nearly forty years until his death, he was concerned with these two
fields. In his research on the spatial changes in gravitation, he used a modified version of
Coulomb's torsion balance. His research method was based on two fundamentals. One was the
strict physical theoretical aspect of the process, and the other, the actual construction of an
unbelievably sensitive instrument, the famous torsion balance
for this research work.
At the beginning Eötvös experimented with his instruments in the laboratory of the
university then later in the garden of his summer house.
He carried out his first field
measurements on Ság Hill in Transdanubia in 1891, where he proved that errors had been
made in the relative pendulum measurements carried out by Sterneck, an Austrian
geodesist in 1884 in the same area.
The first field observation with the torsion balance on |
the Ság hill, in 1891. Eötvös is at the telescope
His first report on gravitation was written in 1888 for the
Academy. In 1896 his fundamental paper, entitled, Studies in the Field of Gravitation and
Magnetism, was published, in which he gave a theoretical and practical summary of his
experiments up to date.
The first experiments on a larger area using the Eötvös balance took place in the winter
of 1901 on the frozen lake Balaton. Eötvös chose the mirror-like frozen surface of the lake to
carry out his measurements so that he would not have to concern himself with the disturbing
effect of topographic masses. He continued his survey work in the winter of 1903, completing
measurements in altogether forty different stations. From the results of his torsion balance
survey it was established that parallel to the axis of the lake ran a tectonic line. The
establishment of this fact was the first geological conclusion based on torsion balance
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In the following years torsion balance surveys were carried out in an ever widening area.
International attention was focused on Eötvös' gravitational experiments when he gave a talk on
the results of his research in Paris in 1900.
The high degree of sensitivity of his instrument was
received with doubt by some. And it was not until the XVth congress of the Internationale
Erdmessung held in Budapest in l906, where he spoke about his latest experiments that these
doubts were entirely dissipated and Eötvös' claims received general recognition. He also made it
possible for foreign participants, who were interested, to observe his torsion balance
measurements on the field in the Arad region. The participants of the conference found Eötvös'
research so significant that they sent a petition to the Hungarian government requesting that
increased financial help be given for gravitational research. The Hungarian government
accepted the suggestion and from 1907 onwards a separate fund was allocated for Eötvös'
gravitational studies. From this time geophysical research was recognized in Hungary as a
separate field in its own right.
Observation site on the ice of the frozen Balaton, 1901|
At first Eötvös' gravitational measurements were carried out for geodetic purposes, but
from the very beginning Eötvös had wondered what geological conclusions could be deduced
from the results of his work. At the XVIIth Congress of the Internationale Erdmessung held in
Hamburg in 1912 Eötvös wrote the following in his report of the practical application of the
"Geologists seem to agree that the most substantial discharges of gas occur
in the immediate vicinity of gas-bearing anticlines, and overlying sediments. Experience
gained in America (Ohio) and observations in Transylvania where the subsurface geological
structures could be determined from superficial indications further endorse these
assumptions. Such geological indications, however, are absent in the sand and humus-
covered surface of the Great Hungarian Plain. He who searches for gas-bearing anticlines in
this or similar areas should not fail to take note of conclusions drawn from torsion balance
In 1916 on the initiative of Hugo Böckh, an eminent Hungarian geologist, torsion
balance measurements were carried out in the region of Egbell (Gbely, Slovakia) where oil was
produced from a recognized anticlinal structure. The aim of these measurements was to
establish the extent to which the effect of the oil-bearing anticline is reflected in the results of
torsion balance measurements. On the basis of the measurements carried out at 92 stations the
contours of the anticlinal oil field were clearly ascertained. These results proved the efficacy of
the torsion balance in oil prospecting and paved the way towards world renown for Eötvös and
his balance. In the 1920 and 30ies hundreds of oil fields were discovered throughout the world
with the help of Eötvös' ingenious instrument.
Eötvös the physicist regarded the geological interpretation of his measurements with
utmost interest, as the following citation proves:
Result map of gravity research. |
Egbell (Gbely), 1916
"Beneath our feet stretches the open country
of the Hungarian Plain, crowned with hills. Over the years this region has shaped itself
naturally, as it wished. I wonder what it was like in former days. What sort of hills have been
eroded and what valleys filled with loose deposits before this fertile area of golden grain came
into being, this life-giving Hungarian Plain? As I walk upon it and eat its bread my mind
dwells upon these questions which would give me such joy to answer."
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Among Eötvös' gravitational instruments, his gravity compensator is also worthy of
mention. This instrument is strictly speaking a curvature variometer provided at both ends with
sector-shaped deflectors, whose position can be changed by rotation about a horizontal axis. If
the deflectors are in vertical position their attraction to the balance is zero, when they are
arranged in horizontal direction their effect is maximum. If the beam of the balance is in the
centre of its case, the attraction of the deflectors is zero because of the symmetrical disposition
but if the beam is not in middle position because some outside mass deflected it from its zero
position, the deflectors become effective since they are now unsymmetrically positioned with
respect to the beam (astatization). Changing the position of the deflectors with respect to the
horizontal direction, the sensitivity of the gravity compensator can be further increased up to the
point of instability. With this instrument Eötvös could register 1 cm changes of the water level
of the Danube from a distance of about 100 m.
Although best known for his torsion balance,
Eötvös also developed a gravimeter. It was completed in 1901, based on the bifilar principle.
The experimental measurements carried out with this instrument, however, failed to meet his
expectations, so he did not publicize his activities in this field. His gravimeter still exists today,
an indication of the wealth of his love for experimentation.
In 1890 Eötvös worked out a method, namely the dynamic method for measuring the
gravitational constant. The basis of his method was the concept that the period of oscillation of
a pendulum placed between two parallel lead walls differed according to whether it oscillated
parallel or perpendicular to the walls. Measuring the periods of oscillation in both positions and
determining the exact mass of the attracting walls the gravitational constant can be calculated.
In physics, mass can be defined in two ways as inertial and gravitational. The inertial
mass of a body determines the acceleration given by an applied force (Newton's second law).
The gravitational mass of the body determines the force it experiences due to the gravitational
attraction of another body.
Eötvös became concerned with the question of the proportionality of the inertial and
gravitational mass as early as 1880.
In 1908 Eötvös and his colleagues, Jenő Fekete and Dezső Pekár, perfected their
measurements to such an extent that they were able to establish that the difference between the
inertial and gravitational mass was at the most 1/20.000.000. Their paper on the subject won
them the Benecke award at the Göttingen University. The experiments carried out by Eötvös
and his colleagues on the proportionality of the inertial and gravitational mass supports
Einstein's theory of relativity.
Eötvös was also interested in the question of gravitational absorption.
He wanted to know, if the mutual gravitational force between two bodies can be changed by
a third body put between the first two.
In the last years of his life, Eötvös carried out experiments which showed that the weight
of moving bodies of the Earth's surface changed depending on the direction and speed at which
they were processing.
It is interesting to note the circumstances that initiated Eötvös' research on this topic. O.
Hecker, an eminent researcher at the Institute of Geodesy in Potsdam led a team to the Atlantic
Ocean in 1901 and then in 1904*1905 to the Indian and Pacific Oceans, to carry out gravity
measurements on moving boats.
While studying Hecker's results in the published report, Eötvös
noticed that no consideration had been given to the forces developed by the motion of the boat.
In a letter to Hecker, Eötvös pointed out his error, but Hecker at first refused to give credence
to this criticism. His colleagues, however, persuaded him that Eötvös was right and so in 1908
new measurements were carried out in the Black Sea to prove this phenomenon. Observations
were made in two boats, one moving towards the east and one towards the west. The results
substantiated Eötvös' claim. The international scientific world recognizes this phenomenon as
the Eötvös Effect. The Eötvös Effect has special importance nowadays in the field of sea and
This experiment is yet another proof of the Earth's rotation, and has even greater
significance than Foucault's famous balance experiment carried out in the Pantheon in Paris.
Experimental tool to model the |
Earth's magnetic field
Parallel to field work with the torsion balance, Eötvös and his colleagues determined the
horizontal component, declination and inclination of the Earth's magnetic field at every
observation point. The extensive observational data available enabled him to give integrated
geophysical interpretation of his measurements.
Measuring the magnetic field direction of ancient bricks and pottery, he tried to
determine the Earth's magnetic inclination in the past.
These experiments can be concidered as the first paleomagnetic measurements.
1900 Eötvös gave a lecture on his studies in this subject, entitled "Magnetic Inclination in the
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