Author: David Aubin

Title: "Le beau climat d'Italie": Jules Janssen, the Spectroscope, and Travel

Abstract: The birth of astrophysics is often presented as the immediate result of the use of new instrumental techniques-photography and especially spectroscopy. Moreover, travel (in particular to sites where solar eclipses could be observed) has also been seen as having played an important role in shaping the emerging discipline. But were these two aspects related to one another?

The case of Jules Janssen who was sent to Italy from October 1862 to April 1863 and then to the Alps in the following year by the French Ministry of Public Instruction show that these two aspects of the process of discipline formation were not independent. In the wake of Kirchoff and Bunsen's famous experiment, Janssen distinguished two categories of lines in the solar spectrum: those due to the sun and those due to the earth atmosphere. After his two missions, he succeeded in establishing not only the existence of telluric lines but also his own credentials and status as savant back in Paris.

In both of these tasks, as I will show in my reconstruction of Janssen's first two spectroscopic missions using unpublished notebooks and correspondence, traveling was crucial. First, Italy's weather allowed him to enjoy more sunshine than he could have had in Paris; the intellectual climate was also better and, as opposed to Paris where Le Verrier kept a tight seal on the Observatoire impérial, he was allowed to use the facilities of Father A. Secchi's Observatory in Rome. Second, Janssen benefited from the recent institutionalization of scientific travel by the French State. One of the earliest form of project-oriented science funding, such missions, I will argue, were seen as a cheap way of fostering national prestige, and they provided a true institutional basis, if only intermittently, for the early development of French astrophysics. Finally, and perhaps more crucially, since the spectroscope mediated between several social groups, the question of their intellectual ownership as well as the property of knowledge produced with their help was raised. The controversies pitting Janssen against his instrument-maker J.-G. Hofmann on the one hand, and Secchi on the other show that status building on the basis of expert manipulation of the spectroscope had to negotiated. Only by traveling to other locations with his spectroscope could Janssen skillfully carve a niche of his own between instrument-makers and professional astronomers.