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Struve Geodetic Arc, a World Heritage Site

The Struve Geodetic Arc is a chain of triangulations that was used to measure the size and shape of the Earth which reaches from the Black Sea to the Arctic Ocean. The triangulations, or the meridian measurement, were an extensive project conducted between 1816 and 1855. The Russo-Scandinavian collaboration was headed by F.G.W Struve. The Russian Academy of Sciences started the measurements in the southern parts of the chain and agreed with Sweden on continuing the measuring efforts from Tornio northwards. Finnish and Norwegian scientists took part in the work under these two realms. The Arc reaches across Finland to Tornio, from where it continues towards north along the region between the Tornio and Muonio Rivers and toward Alta and Hammerfest in Norway. Struve’s measurements were a continuation of the many other expeditions conducted in the northern areas.

The Struve chain

The chain of triangulations was formed by connecting a set of station points marked in the terrain. This enabled mathematically calculating the distances between the station points. The technology at the time required establishing a line of sight between each station point – with the help of available measuring instruments, of course. The distances between the points could be up to tens of kilometres, depending on the visibility between the consecutive points and their locations. For example, the distance between the Alatornio church and the station point in Kaakamavaara is around 35 kilometres. Most of the station points were set up at higher locations with a good visibility of the surrounding environment. Usually, some extra work was required to achieve the line of sight: trees were cut down and marks, or signals, had to be made to make locating the point from a distance easier.

The aim of the project was to measure the length of the imaginary arc on the Earth’s surface, the meridian, more accurately. The measurements were also an important step toward more accurate maps. In addition to angle measurements, the information collected at the station points included elevation and latitude measurements. The research groups used a variety of apparatus from a variety of makers. They also had in their use a rather advanced instrument called a theodolite, which could be used to measure angles both vertically and horizontally.

Measuring the baseline was an important part of the measuring operations, and the measurements were taken at selected sites spanning the entire Arc. The baseline measurements were used to create a scale for the network of triangles. They were measured on flat ground and to the millimetre. The baselines were much shorter than the actual distances between the main station points of the triangles of the Struve Geodetic Arc. They were used to determine suitable points for the triangles. The triangle measurements were carried out until the desired result was reached, i.e. locations were found that would be suitable to be used for the actual measurements. The longest side of the network of triangles eventually formed a line between two station points. These lines were usually around 20–40 kilometres in length. For example, the baseline measured at Ylitornio was converted into a side for the Aavasaksa-Pullinki triangle. After this, measurements could be performed on the entire network of triangles. This means that the lengths of the lines could be calculated based on the measured angles of the triangles. By measuring several baselines, the scientists ensured that the scale was consistent throughout the Arc.

The Struve Geodetic Arc was inscribed on the UNESCO World Heritage List in 2005. All station points of the Arc are important parts of the whole. Some of the station points were selected as world heritage sites to represent this feat of science. The Alatornio church is one the selected world heritage sites.

Alatornio church as a station point

The Alatornio church is one the few station points of the Struve Geodetic Arc that were set up in a building. The church tower was both an excellent measurement location and a good signal when viewed from a distance. The French expedition led by Maupertuis used the tower of the church of Tornio for their earlier measurements. The tower of the Alatornio church was completed after the French expedition in 1979, and it has been preserved as it was when the measurements for the Struve Geodetic Arc were made. Jöns Svanberg also conducted his earlier measurements in 1802 at the Alatornio church. In the 1840s, when the measurements were made, the newer clergy house was constructed, and on the other side of the river, the newly established town of Haparanda was being built.

The surroundings of the Alatornio church were important for the measurements. Many phases of the work took place there. The triangulations and astronomical measurements conducted by the team from the Pulkovo Astronomical Observatory of the Russian Academy of Sciences and the triangulations conducted by the Swedes all took place there. At the end of the measurement work in 1851, the triangulation chain under the responsibility of the Russians and spanning the whole of Finland was connected to the Swedish triangulation chain in the Alatornio church’s area. The Swedes had continued the chain of triangles towards north along the Tornio Valley.

Alatornion kirkko 1896. Museovirasto, historian kuvakokoelma.

The Alatornio church 1896. Photograph: Finnish Heritage Agency, collection of historical photographs

Surroundings of the church

The surroundings of the church and the clergy house on Parasniemi are a valuable cultural heritage site. The Alatornio church and parish are one the earliest sings of permanent settlement in the area. The first church building was built in the 1300s. The current church was built of the foundations of the old stone church near the end of the 1700s.

The Alatornio church has a central location on a hill on the Pirkkiö island. This old religious centre served as a landmark for those who arrived in the area from the direction of the river mouth toward Tornio and the Tornio Valley. The Länsipohja road hugging the coast also ran near the church’s cape. The urban settlements of Tornio and Haparanda were right across the river. However, visitors mainly arrived at the church by boat. Near the church, there once were small cottages maintained by the church for travellers, but they have been worn away by time. The cemetery surrounding the church and its stone fence have slowly expanded, first toward south from the church and later toward the areas east and north of the church. The family names engraved on the stones belong to people from many of the surrounding villages, such as Vojakkala, Kaakamo, Arpela and Pirkkiö. On the southside of the church is the old church granary that was responsible for food supply in days past. Today, the granary houses the Alatornio Museum.

The nearby shores are free of buildings with the exception of Parasniemi, a cape jutting out in the northern end of the island. The Parasniemi clergy house was home to the vicar, whose esteem and title are evident from the impressive buildings. They served to remind the members of the parish of presence of the vicar as well, since they walked past the residence on their way to the church. There are two clergy houses. The high clergy house with a mansard roof was constructed near the end of the 1700s. The other, beautifully restored clergy house was built in the 1840s. In addition to these two main buildings, there is a 200-year-old stone cowhouse and other buildings as well. In the old days, the clergy house had a rather impressive garden with a vegetable field. The larger fields also belonged to the clergy house. The nearest of them are still open fields, but those further away were earmarked for residential construction in the land use plans a decade ago. Parasniemi was a popular landscape both for paintings and for photography – once it was invented. The church tower provides a beautiful view over the cape and the surrounding landscape.

Measurements at the church

Establishing the northern part of the chain of triangulations took years. Work was mainly carried out during summers. As the measurements neared their end, the scientist arrived in the north with a steamship as soon as the waters were clear of ice. The measurements in the Alatornio church area were mainly conducted between 1842 and 1851, during which time the measurements for the Lapland and Finnmark portions of the chain were also made. The church and the nearby Kokkomäki hill were both trigonometrical points, or station points. The church was visible from a large distance, and the view from the church tower also reaches far. However, using the church tower as a station point was challenging, because the measurements had to be taken on the tower’s balcony, which is slightly to the side from the centre of the tower. The centre of the tower also had to be calculated mathematically with angle measurements.

The elevations of the measuring points near the church were measured by the Russians in the autumn of 1842. They finished their triangulations by 1844. The measurements were conducted under the direction of Fredrik Woldstedt, a Finn who worked for the Pulkovo Astronomical Observatory of the Russian Academy of Sciences and in close cooperation with F.G.W Struve. Woldstedt later became a professor of astronomy. This was the endpoint of the Russian-Finnish triangulation chain, which was carried on toward the north by the Swedes. The Swedes started their measurements in the north and measured the angles between the southernmost stations of the Lapland portion of the chain in 1849. Their southernmost triangle was formed by the Alatornio church, Kaamavaara and Perävaara station points. The leader of the Swedish expedition was Nils Haqvin Selander, an astronomist and a member of the Riksdag of the Estates This means research groups from both nations worked in the Alatornio church area.

In 1851, a research group from Russia came to connect the triangulation chains. This expedition was also led by a Swedish scientist: D.G. Lindhagen who worked for the Pulkovo Astronomical Observatory. When looking for a site for the astronomical studies is 1851, the area of the church was found to have many benefits when compared to Kemi, for example. The Alatornio church had already served as a measuring point for Jöns Svanberg and it was the southernmost station point for the Swedish part of the triangulation chain. In addition to the church building itself, the surrounding area was suitable for the task due to it being a central location and still not being too densely populated. The scientists wanted to be able to work in peace. The surroundings also included some open areas and sand hills that could be used to assist in the measurements. Some very valuable research equipment was stored at the research station, which meant it had to be under guard at all times when the scientists were away.

The research station was built on the open area near the church (distance from the church 860 feet, or 279 metres). The triangulation chain was aligned on the surface of the Earth with the astronomical measurements made at the research station. Exact locations were determined for the points by observing the locations and movement of stars. The research station was connected to the Alatornio church, the town church and the Kokkomäki hill nearby with a shorter baseline (length 523 feet, or 170 metres) and triangulation. This baseline was measured by using a pole that was exactly 22 feet in length and placed on top of three-legged stands.

Lindhagen’s group waited for Selander to arrive from Stockholm, and when he arrived, Lindhagen’s group put their own research on hold and went to measure the official longer baseline in Ylitornio with Selander. The measurements for the baseline were conducted by teams from both nations during that summer and the teams exchanged information and skills between them.

The scientists and their assistants and underlings also visited Kaakamavaara and Kivalo in 1851, where they measured the angles to the Alatornio church and to Kokkomäki. During these measurements, made for connecting the Swedish and Finnish chains, a proper line of sight could not be established to Kokkomäki, which was the last main station point of the Finnish chain. However, the church tower was visible, and the scientists deemed that to be sufficient for taking the measurements. The church was also a main trigonometric point for the Swedes. In practice, after the chains were connected, one of the triangles of the chain was formed by Kivialo, Ajos and the Alatornio church. Naturally, as the massive project progressed, some challenges were faced, and compromises had to be made.

The station points were usually marked in the terrain in a long-lasting manner to ensure that the measurements were exact and that the points could be reused later. In addition to station points in the terrain, the Alatornio church was used in the triangulation. The measuring instrument was most likely placed on a separate table on the church tower’s balcony. This table is there. The tower’s bell chamber has engravings from 1851, possibly made by members of Lindhagen’s research group. The Kokkomäki station point, filled with lead, was found to be in its original condition in an inventory conducted at the start of the 1900s. Later, more land was brought to the location, but the station point is marked with a metal pole.

Church tower

The church tower reaches 40 metres above sea level. The lower part of the tower is massive, but the higher structure is more delicate. The strong structures are visible inside. One can only wonder at the skill of the people who build the tower when looking at its handmade structures. The larger part houses a large bell chamber with the church bells. The hatches of the windows – all facing different directions – are opened when the bells are rung. This part of the tower has a balcony around it, where the measuring instrument is thought to have been used. There may have been measuring tables on the other side of the tower as well, but one at least is sure to have been on the railing on the eastern side of the tower. The stairs continue up to the second platform and eventually reach the top of the tower. There, a small room with windows serves as lovely vantage point. It is a marvel that visitors can still admire the view just like the people visiting the tower 200 years ago did. However, the tower is not open to public.

The signals used for the triangulation can still be seen on the horizon from the tower, and the church can be seen from these points as well. Kaakamavaara hill and the lower Perävaara hill are visible when looking toward the northern section of the chain. Of the hills further away, Nivavaara is visible and so is the station point on Huitaperi even further away. When looking toward the southern parts of the chain, both the station points of Kallinkangas and Kivalo’s Alapenikka can be seen. There used to be a line of sight to the station point in Ajos as well. Many signals were also visible from Kokkomäki, but today, trees break the line of sight at many places.

Text: Jarno Niskala, Tornio City / ‘Maailmanperintö Struven ketjun pohjoiset osat’ project (Northern part of the Struve Geodesic Arc, a World Heritage Site)