208
Ecuador) organized by C.M. de la Condamine (1703–1774). These measures confirmed Newton’s polar flattening (Boccaletti 2019).
However, the measurements of global meridian arcs did not account for total
north-south extension of Central Europe. Thus in 1862 the Prussian general
J.J. Baeyer (1794–1885) decided to organize an international conference (1864) to
which both Italy and the Papal States were invited (Torge 2005, 2012). The Papal
States held off taking up their membership given the friction with the Kingdom of
Italy due to the Roman Question; eventually, however, at the end of 1869, the Holy
See decided to join the project.
Despite this, Secchi was invited to take part in the sessions of the Italian
Commission for the Measure of Degrees (which became the Italian Geodetic
Commission in 1880) to describe the geodetic activities that had been carried out by
the Papal government. In his report he described the problems and the extent of the
geodetic baseline along the Via Appia Antica that had been measured 15 years earlier. Following the report, Italy decided to officially invite the Papal government,
since a long stretch of that the meridian lay in papal territory.
In December 1869 the Holy See set up a mixed commission of astronomers and
military engineers, with Secchi as president, to deal with the international geodetic
operation. The official announcement of the triangulation work in the Papal States
was published in February 1870, with instructions to individuals not to hinder geodetic operations. The first tasks of the Pontifical Commission were to choose the
places where the geodesic stations would be placed and to obtain the necessary
instruments (Aebischer 2016).
Rome, of course, remained at the center of the triangulation. Around it a closed
polygon was drawn joining the points of Pratica, Mount Virginio, Mount Soratte,
Mount Gennaro, Mount Cavo, and, again, Pratica. Within this polygon was the geodetic baseline measured in 1855. Rather than keeping the main station centered on
the cross of the dome of the basilica of Saint Peter, the cartographic reference
meridian of the Papal States, the top of the highest mountain in Rome, Monte Mario,
was chosen instead, from which all the measurement stations could be seen. After
inspecting various sites, the Pontifical Commission chose a point within the vineyard of Prince Barberini, Duke of Castelvecchio. An agreement was signed with the
prince, and, following the directions of Major Oberholtzer, the first stone of the
square-based tower was laid in May 1870.
The base of the tower measured 4.66 m on the side, and the total height was
12.85 m. At the base of the northern side of the tower was an entrance door, and the
tower included three windows for astronomical observations, including a small balcony protected by a railing. Inside the tower a spiral staircase led up to the rooftop.
A small pillar was built at the center of the rooftop: this was the fundamental trigonometric point. To indicate this point and make it more permanent, at this spot a
stone of 60 × 60 cm, 50 cm thick, was placed at a depth of 4 m below the threshold
of the entrance door, supported by the underlying layer of volcanic tuff. A hole
through the center was aligned with the axis of the tower and the summit pillar, and
it bore the inscription: 1870 SEGNALE / TRIGONOMETRICO / PIUS IX P.M.
T. Aebischer
Ecuador) organized by C.M. de la Condamine (1703–1774). These measures confirmed Newton’s polar flattening (Boccaletti 2019).
However, the measurements of global meridian arcs did not account for total
north-south extension of Central Europe. Thus in 1862 the Prussian general
J.J. Baeyer (1794–1885) decided to organize an international conference (1864) to
which both Italy and the Papal States were invited (Torge 2005, 2012). The Papal
States held off taking up their membership given the friction with the Kingdom of
Italy due to the Roman Question; eventually, however, at the end of 1869, the Holy
See decided to join the project.
Despite this, Secchi was invited to take part in the sessions of the Italian
Commission for the Measure of Degrees (which became the Italian Geodetic
Commission in 1880) to describe the geodetic activities that had been carried out by
the Papal government. In his report he described the problems and the extent of the
geodetic baseline along the Via Appia Antica that had been measured 15 years earlier. Following the report, Italy decided to officially invite the Papal government,
since a long stretch of that the meridian lay in papal territory.
In December 1869 the Holy See set up a mixed commission of astronomers and
military engineers, with Secchi as president, to deal with the international geodetic
operation. The official announcement of the triangulation work in the Papal States
was published in February 1870, with instructions to individuals not to hinder geodetic operations. The first tasks of the Pontifical Commission were to choose the
places where the geodesic stations would be placed and to obtain the necessary
instruments (Aebischer 2016).
Rome, of course, remained at the center of the triangulation. Around it a closed
polygon was drawn joining the points of Pratica, Mount Virginio, Mount Soratte,
Mount Gennaro, Mount Cavo, and, again, Pratica. Within this polygon was the geodetic baseline measured in 1855. Rather than keeping the main station centered on
the cross of the dome of the basilica of Saint Peter, the cartographic reference
meridian of the Papal States, the top of the highest mountain in Rome, Monte Mario,
was chosen instead, from which all the measurement stations could be seen. After
inspecting various sites, the Pontifical Commission chose a point within the vineyard of Prince Barberini, Duke of Castelvecchio. An agreement was signed with the
prince, and, following the directions of Major Oberholtzer, the first stone of the
square-based tower was laid in May 1870.
The base of the tower measured 4.66 m on the side, and the total height was
12.85 m. At the base of the northern side of the tower was an entrance door, and the
tower included three windows for astronomical observations, including a small balcony protected by a railing. Inside the tower a spiral staircase led up to the rooftop.
A small pillar was built at the center of the rooftop: this was the fundamental trigonometric point. To indicate this point and make it more permanent, at this spot a
stone of 60 × 60 cm, 50 cm thick, was placed at a depth of 4 m below the threshold
of the entrance door, supported by the underlying layer of volcanic tuff. A hole
through the center was aligned with the axis of the tower and the summit pillar, and
it bore the inscription: 1870 SEGNALE / TRIGONOMETRICO / PIUS IX P.M.
T. Aebischer