Gressot Julien
Historian of Science and Technology | Specialist in Observatories, Time Measurement, and Scientific Instruments
I am a historian of science and technology specializing in the history of astronomical observatories, the measurement of time, and the material culture of science in the 19th and 20th centuries. My research examines the interactions between scientific practices, instrumentation, and the institutional, political, and cultural contexts in which they evolved.
My doctoral thesis, L’Observatoire cantonal de Neuchâtel et la mesure du temps (1858-1960): instruments scientifiques, acteurs et espaces savants (University of Neuchâtel, 2024), explored the Observatory’s role in global networks of astronomical and time measurement, combining archival analysis, object studies, and methodological tools such as the operating chain.
I am currently a postdoctoral researcher at the University of Neuchâtel on the Swiss National Science Foundation interdisciplinary project Atomic Clocks at the Neuchâtel Observatory: Time, Quantum Technologies and Innovation (1948–2001), led jointly by the Institute of History and the Time-Frequency Laboratory. This position allows me to work closely with physicists, engineers, and historians on the intersections of science, technology, and innovation.
Alongside my academic research, I am deeply engaged in museum-based knowledge transfer. I am project leader for the Automates & Merveilles initiative, developing the scientific content and overall coordination for the exhibition Des étoiles aux atomes… L’Observatoire cantonal de Neuchâtel, which will open in June 2026 across three sites: the Musée d’art et d’histoire de Neuchâtel, the Musée international d’horlogerie in La Chaux-de-Fonds, and the Musée d’horlogerie du Locle – Château des Monts. I also serve as curator or scientific advisor for other exhibitions in Switzerland, bridging public history and scholarly research.
I am a historian of science and technology specializing in the history of astronomical observatories, the measurement of time, and the material culture of science in the 19th and 20th centuries. My research examines the interactions between scientific practices, instrumentation, and the institutional, political, and cultural contexts in which they evolved.
My doctoral thesis, L’Observatoire cantonal de Neuchâtel et la mesure du temps (1858-1960): instruments scientifiques, acteurs et espaces savants (University of Neuchâtel, 2024), explored the Observatory’s role in global networks of astronomical and time measurement, combining archival analysis, object studies, and methodological tools such as the operating chain.
I am currently a postdoctoral researcher at the University of Neuchâtel on the Swiss National Science Foundation interdisciplinary project Atomic Clocks at the Neuchâtel Observatory: Time, Quantum Technologies and Innovation (1948–2001), led jointly by the Institute of History and the Time-Frequency Laboratory. This position allows me to work closely with physicists, engineers, and historians on the intersections of science, technology, and innovation.
Alongside my academic research, I am deeply engaged in museum-based knowledge transfer. I am project leader for the Automates & Merveilles initiative, developing the scientific content and overall coordination for the exhibition Des étoiles aux atomes… L’Observatoire cantonal de Neuchâtel, which will open in June 2026 across three sites: the Musée d’art et d’histoire de Neuchâtel, the Musée international d’horlogerie in La Chaux-de-Fonds, and the Musée d’horlogerie du Locle – Château des Monts. I also serve as curator or scientific advisor for other exhibitions in Switzerland, bridging public history and scholarly research.
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In order to remain a reference in this field, The Neuchâtel Observatory seized the opportunity to update its time service. Used between 1954 and 1982, the instrument is seen as significantly reducing instrumental errors and eliminating the personal equation.
To explain the issues involved in the transition from the meridian method to the zenithal method, this talk intends to start from the material culture of the scientific instrument confronted with the study of the technical documentation and the archives of the Observatory.
Papers by Gressot Julien
Conference Presentations by Gressot Julien
This talk aims to analyse the implementation of this apparatus for determining, keeping and transmitting the time, through the reconstruction of a “chaîne opératoire” allowing to visualise both the arrangement of scientific instruments and the daily operations of astronomers. Drawing on the skills of a conservator of scientific instruments and a historian of science, this “chaîne opératoire” is the result of the analysis of the Observatory of Neuchâtel’s instruments collection and the analysis of the Observatory's archives.
The Meridian circle was delivered in September 1859, and it has since been meticulously studied in order to determine its instrumental errors. Once operational, Hirsch used it for his research on the personal equation in order to minimize the observer's errors from the data. This quest to obtain the most accurate result possible continues until the replacement of the meridian circle in 1912.
Introducing the Ertel Meridian Circle and the richness of correspondence that surrounds it allows us to study the establishment of a culture of precision at the Neuchâtel Observatory. How does a newly created Observatory manage to make its place in the international network of scientific institutions? What strategies does the Observatory implement to acquire this reputation of precision over time and what place do scientific instruments and the Ertel & Son Meridian Circle occupy in it? The aim of this talk is to answer these questions and to show the steps involved in obtaining a high-precision scientific instrument and keeping it in operation for more than half a century.
Sohn à Munich. Cet instrument sert à déterminer l’heure en observant l’instant de passage des astres dans le plan méridien. L’astronome a l’intuition d’utiliser la méthode chronographique – introduite en Europe par George Airy (1801-1892) à l’Observatoire de Greenwich -, ce qui
permet d’augmenter le nombre de données enregistrées grâce à la combinaison du cercle méridien, d’un chronographe et d’une horloge sidérale. Cette mise en réseau électrique et le plus grand nombre de données permettent l’obtention de mesures d’une plus grande précision
que celles obtenues par d’autres méthodes. Adolphe Hirsch n’a de cesse de vouloir améliorer cette précision, notamment lorsqu’il effectue des recherches sur l’équation personnelle afin de réduire l’influence de l’observateur sur la production des données.
Cette présentation entend décrire la première chaîne opératoire de la détermination de l’heure de l’Observatoire de Neuchâtel, effective en 1861, à partir de sa culture matérielle sous la forme d’une illustration cartographique. La richesse des archives de l’institution, les échanges entre les fabricants et l’Observatoire ainsi que l’étude de la matérialité de certains instruments et de dessins techniques permettent de voir les besoins scientifiques des astronomes et les possibilités techniques des fabricants. Cette correspondance constitue un témoignage précieux sur les discussions et négociations entourant la mise en place d’une culture de la précision astronomique dans une région horlogère, le canton de Neuchâtel, durant la seconde moitié du XIXe siècle.
Drafts by Gressot Julien