This contribution aims at questioning two common metaphors in geoscience education about seismographs. We scrutinize them to address the issue of “the paradox that analogy both misleads and leads people to better understanding” (Aubusson, Harrison & Ritchie, 2006). In the first metaphor, seismographs record earthquakes as a person would write during (fictive) shakings of the ground. In the second metaphor, seismometers record earthquakes in the same way as a person in an elevator would feel an acceleration when going up. We study the first metaphor in the context of fifth grade classroom sessions conducted by two teachers. In France, earthquakes are a teaching content of primary school science education. Our data consist of the transcripts of two videotaped classroom sessions and of the audiotaped teachers’ interviews before and after the session. We analyze the whole corpus (Santini, 2007) with a clinical approach to ordinary classes (Schubauer-Leoni & Leutenegger, 2002) and an a priori analysis formatted as a grid (Buty, Tiberghien & Le Maréchal, 2004). We situate our work within the Joint Action Theory in Didactics (Sensevy & Mercier, 2007; Sensevy, 2008). We also use a model of description (Sensevy, Schubauer-Leoni, Mercier, Ligozat & Perrot, 2005) based upon didactic categories (Brousseau, 1997; Chevallard, 1992). During the classroom sessions, the two teachers introduce similarly the working of seismographs by the means of ostensive actions. They both present the general working of this distant instrument as analogous to the particular working of a well-known writing tool, a chalk or a pen, through miming actions. This operation of reduction to the particular (Cartwright, 1999 ; Sensevy, Tiberghien, Santini, Laubé, & Griggs, in press) makes visualisable the working of a seismograph: the stylus of a seismograph during an earthquake behaves like the chalk or the pen in the teacher’s hand during a shaking. We identify and formalize, according to Eco (1986), this utterance as a metaphor by proportion: stylus/seismograph = chalk/teacher. At first sight, such a metaphor may seem too obvious to be really opened for interpretation. But, Eco claims that “no metaphor is absolutely ‘closed’: its closure is pragmatic”. Relying on his work, we account for the process of semiosis which make a student, in Eco’s terms, disambiguate this metaphor and which provide a joint understanding of the action (Sensevy, 2008). We analyze the same way the second metaphor: the working of a modern seismometer in reference to the relative movement of a person in an elevator. We study an example of the use of such a metaphor in a science popularization book authored by a seismologist (Bernard, 2003). Bernard makes concrete his explanation of the abstract working of seismometers by comparing the relative moves of the mass within the frame of the instrument to those of his reader in an elevator. Here, the metaphor by proportion is: mass/frame = reader/elevator. In the same way as previously, we account for the process of semiosis which make the reader disambiguate this second metaphor. Finally, we compare these two metaphors and conclude on their role in the teaching and the learning of seismology.

We follow a clinical approach to ordinary classes (Schubauer-Leoni & Leutenegger, 2002). In such an approach, we neither participate nor intervene in the teaching except by videotaping the classroom sessions. We interview the two teachers three times: the two teachers together before the session, each teacher separately after the session and the two teachers together also after the session. The whole corpus is transcribed and analyzed.

In both cases, the use of metaphors reduces to a particular a general principle and give a concrete content to the abstract working of a distant instrument. This concrete content is given by referring the unfamiliar world of seismographs to the more familiar worlds of writing, especially in a classroom, and of elevators. Building such relations between different worlds contributes to the assimilation by students of a thought style specific to the scientific knowledge at stake (Sensevy et al., in press). On the one hand, the analyzed metaphors set a common cognitive context for the teacher and the students, or for the author and the readers, and supply them with a pragmatically operative tool for the study of earthquakes, notably imperceptible ones. On the other hand, both of these metaphors may lead to the same confusion between absolute and relative movements of the basic elements of seismographs.