Instrumental Measurements
Some early measurements with instruments date back to the 17th century and become significantly more numerous and reliable from the middle of the 18th century. However, they must always be analysed critically. This applies to the instruments themselves, their positioning, the timing of the readings and any changes to these conditions. Early thermometers were not weatherproof and were usually hung inside buildings. They were also exposed to the sun at times. In general, temperature measurements in the heat islands of larger settlements are too high. In the best case scenario, these framework conditions can be checked using the operating logs. This is the only way to homogenise measurements, i.e. to make them comparable in terms of time and space. Only the HISTALP series from 1774 onwards is homogenised for the Alpine region (Auer et al. 2007). The homogenised temperature series from Paris goes back to 1659 (Rousseau 2012).
Today's measurements are carried out as far away from settlements as possible in so-called weather huts two metres above the ground. For measurements under other conditions, the size of the measurement error must be specified.
Measuring devices
Father Louis Cotte, canon at Laon Cathedral, was a scientist associated with the Académie des Sciences in Paris and the Societas Meteorologica Palatina in Mannheim (Baden-Württemberg), which set up an extensive international meteorological measurement network. His Mémoires show the best meteorological instruments of his time. Barometers had been common in wealthy households since the early 18th century.
This mercury-glass thermometer was made by the Lyon instrument maker Pierre Casati around 1790. It was one of the first thermometers to use the scale invented in 1742 by the Swedish astronomer Anders Celsius (1701-1744) and named after him. However, the Celsius scale was originally downwards, with a value of 0 ºC for the boiling point and 100 ºC for the freezing point of water. Jean-Pierre Christin, a member of the Société Royale of Lyon, reversed the scale in 1743 so that the freezing point corresponded to 0 ºC and the boiling point to 100 ºC. This is noted next to the scale of this thermometer, which can display values between -35 ºC and 100 ºC. Thermometers were common in wealthy households from the middle of the 18th century onwards.
In contrast to barometers and thermometers, which were manufactured in large quantities and marketed by merchants, precipitation gauges had to be made individually by craftsmen according to plans. This is probably one reason why precipitation measurements were relatively rare before the 19th century. As the rain gauges were also exposed to wind and weather, they have only survived in exceptional cases and are largely only known from drawings in publications. Historical precipitation measurements are inaccurate for several reasons. The containers must be protected against evaporation losses and frost. In addition, precipitation must not be obstructed by nearby buildings and trees. In 1760, the Oekonomische Gesellschaft Bern had a rain gauge (pluviometer) constructed for its meteorological measuring network, which reduced evaporation losses by allowing the water to flow from the funnel-shaped collecting vessel through a narrow pipe into a storage vessel. A statistical review of the Bernese precipitation measurements showed that they were qualitatively comparable with today's measurements (Pfister 1975).
In 1808, a Rhine gauge was installed at the Schifflände in Basel at Switzerland's water gate, which is still read daily today. In this 200-year, longest continuous discharge series in Switzerland, extreme high and low water levels emerge, from which conclusions can be drawn about exceptional precipitation events and dry periods (Pfister, Weingartner, Luterbacher 2006; Wetter et al. 2011).
Pioneers of instrument measurement in Switzerland
From 1708 to 1733, the Zurich (city) doctor, natural scientist and polymath Johann Jakob Scheuchzer (1672-1733) was the first to carry out instrumental measurements of air pressure, air temperature and precipitation in his house in Zurich's Niederdorf district - albeit not without gaps - and read the water level of the Limmat from a gauge. He published some of the results in scientific journals such as the Mémoires de l'Académie des Sciences in Paris and the Philosophical Transactions in London. He wrote his commentaries in Latin, the scholarly language of the time (Pfister 1999: 27). His main work, the three-volume "Natur-Geschichte des Schweitzerlands", is publicly accessible in digitalised form.
Frédéric Moula (1703-1782), a mathematician from a family of Huguenot refugees, kept a weather diary in Neuchâtel from 1753 until his death, in which he recorded thermometric and barometric measurements three times a day. He used a Fahrenheit thermometer. Although the Neuchâtel mathematician and scientist Charles-Guillaume Kopp held out the prospect of a complete publication of the weather diary as early as the 19th century, this never materialised. It was not until the meteorologist Max Schüepp calculated monthly averages from Moula's daily temperature measurements (Schüepp 1961), which were incorporated into Euro-Climhist.
Johann Jakob d'Annone (1728-1804), a lawyer, taught Roman law, numismatics, mathematics and natural history from 1759. In 1766 he was appointed professor of eloquence at the University of Basel and in 1779 professor of codex and feudal law. He is regarded as a "representative of the encyclopaedic age" (Andreas Staehelin). Five of his numerous publications concerned meteorology and a further five his actual speciality, fossils (Staehelin 1957: 321). From 1755 until his death in 1804, he carried out daily measurements of temperature and air pressure as well as weather observations in his house at Heuberg 16 in Basel. Max Bider, Max Schüepp and Hans von Rudloff (1959) homogenised the temperature series, but the reconstructed summer temperatures are still somewhat too high (Auer et al. 2007).
The Geneva meteorologists of the late 18th century
After 1760, several scientists in Geneva were involved in meteorological observations and measurements, with the Société des Arts, founded in 1776, serving as a forum for scientific exchange (Grenon 2010).
Charles Benjamin, Baron de Lubières (1714-1790), scion of a Huguenot refugee family and member of the Grand Council, measured temperature, air pressure and precipitation daily from 1770 to 1789 and recorded wind direction, sky coverage and vegetation development. In summer he lived in Petit Saconnex near the former town, in winter in Geneva on Rue de Beauregard. His observations, preserved in the archives of the University of Geneva Observatory in Sauverny, have since been analysed (Gautier 1843; Häderli 2015). His precipitation measurements from 1771 to 1777, which were followed by those of the observatory from 1778 onwards, are of particular value in terms of climate history (Grenon 2010).
Guillaume-Antoine Deluc (1729-1812), a brother of the famous physicist and geologist Jean-André Deluc, was a member of the Grand Council of his home town and had been interested in scientific observations, particularly meteorology and geology (fossils), since his youth. He climbed numerous peaks in the Mont Blanc massif with his brother. From 1768 onwards, Guillaume-Antoine Deluc kept a weather diary with instrumental measurements (Gautier 1843: 3), which were analysed by Max Schüepp (1961) and Stefan Häderli (2015) (Series 7).
Marc-Auguste Pictet (1752-1825), a legal adviser to the Grand Council, devoted himself to physics and meteorology. From 1779 onwards, he was responsible for observations at the observatory founded in 1773 (Grenon 2010).
The precipitation series of Geneva (1771 to the present), one of the longest in Europe, is made up of the measurements of Baron de Lubières (1770-1777), those of the Observatoire (1778-1863) and those of the measuring station(s) of today's MeteoSwiss. It was first published in Euro-Climhist, but the values for the period before 1864 have not yet been homogenised (Sigrist 1990). In 1782, the Societas Meteorologica Palatina, founded in 1780, chose Geneva as the measurement location, with the chief librarian Jean Senebier (1742-1809) carrying out the measurements (Grenon 2010). The Societas Meteorologica Palatina equipped its measuring stations in Europe with standardised instruments, set standardised measuring times and published the results in a yearbook.