Grégory Quenet
52
nord-ouest. Le baromètre était à 26 pouces 6 lignes 1/2 le thermomètre a I d ½ audessus de 0. Le vent très foible à l’ouest, les jours précédents avoient été les plus
froids de l’année avec le vent au nord. A 7 heures du matin, j’observai le 6 le
thermomètre de M. de Réaumur à 6 ½; le 7 à 7 ¼, le 8 à 7, et le 9 à 0. […] Tout
l’effet du tremblement s’est borné à renverser quelques outils dans des cabinets
d’horlogers logés au haut des maisons, et à faire sonner quelques cloches.
50
To the initial reporting framework were added the lapse of time between shocks, their direction, the weather conditions (air pressure,
temperature, wind direction, etc.), specifying where necessary any coincidence with other unusual phenomena (storms, comets, fogs). With
a greater or lesser degree of rigour and exhaustiveness, the reports on
seismic activity sent to the Académie des sciences followed this pattern.
Knowing the time at which an earthquake struck was fundamental. A simultaneous shock occurring at two different points allowed scientists to conclude that they were dealing with the same
phenomenon and a single cause. If a slight chronological discrepancy
existed between the shocks, this focussed investigations on the physical mechanics of the earthquake: how did a shock occurring at a central point spread? What was the speed of its propagation? Such
questions demanded an increased level of precision in order to corroborate proofs, calculate velocities and establish the physical geography of an area. Scientific accounts of the time paid close attention to
determining the direction of land movements where these occurred so
as to arrive at a more general understanding of the phenomenon. Directions of land movements indicated the epicentre of earthquakes and
synthesizing this sort of information enabled scientists to link up spatially dispersed events. Measuring the duration of shocks provided yet
another element of comparison as well as suggesting further trails of
enquiry for geophysical theory. It was (and is still) an implicit means
of assessing the intensity of the shock. Empirically, contemporaries
believed that the duration of the tremor determined, among other
things, the extent of the material damage sustained. Comparing the
earthquake that hit Aix on 3 July 1756 with the firsthand accounts of
the Lisbon disaster of 1 November 1755, one witness of the former
explained that “les secousses furent moins violentes [à Lisbonne] que
celles que nous avons ressentis ici, mais qu’à la vérité elles furent
___________________________
50 Académie royale des Sciences, Registre des Procès-verbaux des séances, 31 janvier
1756, vol. 75, fol. 55.
52
nord-ouest. Le baromètre était à 26 pouces 6 lignes 1/2 le thermomètre a I d ½ audessus de 0. Le vent très foible à l’ouest, les jours précédents avoient été les plus
froids de l’année avec le vent au nord. A 7 heures du matin, j’observai le 6 le
thermomètre de M. de Réaumur à 6 ½; le 7 à 7 ¼, le 8 à 7, et le 9 à 0. […] Tout
l’effet du tremblement s’est borné à renverser quelques outils dans des cabinets
d’horlogers logés au haut des maisons, et à faire sonner quelques cloches.
50
To the initial reporting framework were added the lapse of time between shocks, their direction, the weather conditions (air pressure,
temperature, wind direction, etc.), specifying where necessary any coincidence with other unusual phenomena (storms, comets, fogs). With
a greater or lesser degree of rigour and exhaustiveness, the reports on
seismic activity sent to the Académie des sciences followed this pattern.
Knowing the time at which an earthquake struck was fundamental. A simultaneous shock occurring at two different points allowed scientists to conclude that they were dealing with the same
phenomenon and a single cause. If a slight chronological discrepancy
existed between the shocks, this focussed investigations on the physical mechanics of the earthquake: how did a shock occurring at a central point spread? What was the speed of its propagation? Such
questions demanded an increased level of precision in order to corroborate proofs, calculate velocities and establish the physical geography of an area. Scientific accounts of the time paid close attention to
determining the direction of land movements where these occurred so
as to arrive at a more general understanding of the phenomenon. Directions of land movements indicated the epicentre of earthquakes and
synthesizing this sort of information enabled scientists to link up spatially dispersed events. Measuring the duration of shocks provided yet
another element of comparison as well as suggesting further trails of
enquiry for geophysical theory. It was (and is still) an implicit means
of assessing the intensity of the shock. Empirically, contemporaries
believed that the duration of the tremor determined, among other
things, the extent of the material damage sustained. Comparing the
earthquake that hit Aix on 3 July 1756 with the firsthand accounts of
the Lisbon disaster of 1 November 1755, one witness of the former
explained that “les secousses furent moins violentes [à Lisbonne] que
celles que nous avons ressentis ici, mais qu’à la vérité elles furent
___________________________
50 Académie royale des Sciences, Registre des Procès-verbaux des séances, 31 janvier
1756, vol. 75, fol. 55.