Edge of the Old World

The post on the meridians pointed out a few important prime meridians and waited for information on further local prime meridians. From the description of the post it is clear that there are two main types of them.

The absolutely local meridians essentially all fix on the floor the trace of a light beam projected through a hole in the dome or high ceiling, a camera obscura, thus demonstrating the passing of time throughout the year. Such was the one made by G. D. Cassini in Bologna, but they designed similar ones almost everywhere, where extensive closed spaces were available. It was certainly a pleasant feeling to follow on the floor the path of the little light dot, the circular image of the Sun, passing through the line of the meridian, indicating both the noon and the place of the months and days.

The camera obscura designed in the vault of the Basilica di San Petronio in Bologna, and the image of the Sun at noon

The much more important local meridians were marked practically in every major observatory, since the basis of any observation is the precise setting of the local noon.

Accordingly, a large number of local prime meridians are known. As many observatories, as many local meridians. But only a few of them had the privilege to be accepted by the international society of cartographers as a generally valid prime meridian. Besides the already mentioned London and Paris meridians, the so-called Ferro meridian, that is, the meridian passing through El Hierro enjoyed a certain priority, which is also worth to mention because of its Central European reference. Indeed, the Austrian Empire, the Austro-Hungarian Monarchy, and the inter-war military maps all used it as the 0° of their geographical coordinates.



How was this location picked out? Already in Ptolemy’s system of longitudes and latitudes, the westernmost point of the then known world was chosen as a prime meridian, thus providing a positive value to all the meridians in the continent. During the geographical discoveries it turned out that the Canary Islands are located much further west than any part of Europe. Thus they defined the prime meridian here, at the farthest point of the Old World – due to the inaccuracies of the measurement, round twenty degrees west of Paris.

The cartographers, by following the traditions of their place of operation, widely used the Ferro meridian as well as the generally accepted London and Paris meridians.

One of the earliest maps produced in Hungary was the work of students-engravers in Debrecen who, under the direction of Ézsaiás Budai, designed and printed the first school atlas in Hungarian language. Both the Paris and Ferro degrees were indicated on the edge of the maps: below that of Paris, and at the upper edge that of Ferro.

Frontispiece of the Oskolai magyar új átlás (New Hungarian school atlas) and the map of France in it

Germany and the Austro-Hungarian Monarchy (as well as its succession states) officially published all topographic maps with the Ferro meridian as long as the end of the Second World War.

1:200 000 scale general map of the Monarchy – TRIEST 31°46°

The 1:200 000 scale map of Trieste, for example, bears in the name the Ferro latitude and longitude running through the midle of the map section, and only that. After the war they at least started to mark with guard lines on the edge of the sections the Greenwich degrees as well.

The 1:75 000 military map of Sopron from the interwar period. The frame already indicates by guard lines the Greenwich degrees, too

But in order to see a printed country map which, in contrast to the international custom, was printed with a local longitude system: in 1753 András Frisch designed his map of Hungary on the basis of the data of Sámuel Mikoviny, the renowned 18th-century engineer and cartographer, with a longitude system based on the Pozsony (today Bratislava) prime meridian.

TABULA NOVA INCLYTI REGNI HUNGARIAE juxta nonnulas Observationes Samuelis Mikoviny. Concinnata Ab Andrea Erico Fritsch Posonii 1753

And once we spoke about Trieste…

Trieste is an important location in the Hungarian geodetic and engineering practice. As many prime meridians, as many zero sea levels to specify any geographic altitude. You only need a sea to it. But where, when which one? The zero sea level of the Austro-Hungarian Monarchy was for example established and fixed with a “golden nail” in 1875 on the basis of the observations of many years of the mareography of Trieste’s Molo Sartorio, using it as a starting point for altitude measuring throughout the Empire.

The sea level observation stations in Trieste and Kronstadt

In addition, because of the great distances, the exact altitude above the sea level was recorded, by way of multiple measurements, in a granite quarry of Nadap above the Velencei Lake in Hungary, assuming that granite is relatively stable, and the altitude fixed there will not change during the slow movements of the Earth’s crust.

The starting point of Hungarian altitude measuring, the Basic Sign of Nadap

At present, in Hungary they officially use the Baltic zero sea level, deduced from the sea fluctuations at Kronstadt for the Soviet system maps. When connecting the two basic levels, it turned out that the Adriatic values were approximately 67 centimeters lower than the Baltic ones.

And to satisfy the request of the previous post on meridians: the prime meridian of the above 18th-century map of Hungary, the Meridionalis Posoniensis has not passed without a trace either. The memory of this prime meridian has been immortalized under the castle, on the promenade along the Danube.

Memorial stone of the Pozsony (Bratislava) prime meridian, which points at the northeastern tower of the castle.

If the interested readers will report on the prime meridians known to them, would they also be so kind to tell whether there are any other zero sea level marks, and where? In Britain, in the Netherlands… Anywhere where they produce relief maps, and indicate on it the altitudes above sea level.