Since the inception of the modern atomic theory, chemists have used physical models to represent the structure of molecules. The goal of this paper is to bring molecular modelling into focus as a constitutive yet overlooked element of chemical practices. It begins with a short technical introduction to molecular models, and then moves into a participant-centred analysis of molecular modelling. Central points of this analysis include, first, a discussion of the dichotomy between graphical and material forms of representation, with suggestions about its consequences for a semiotically-centred view of scientific activity; and, second, a look at the problem of the interpretation of molecular models, as discussed in the chemical literature. The last section focuses on the design of modelling systems through two related historical case studies — namely, the production of two space-filling modelling kits developed in the United States between the late 1930s and the late 1960s.

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Since the development of structural theory and stereochemistry in the mid to late 19th century, to understand a molecular compound, to account for its physical and chemical properties, has been very much a matter of knowing and understanding its structure. The notion of molecules as discrete three-dimensional structures, a theoretical construct developed through and mobilized in the process of accounting for the properties of matter, has proven over time to be, by all accounts, a heuristically powerful formal gloss.Historically, the development of classical structural theory in chemistry has been concomitant with the development of non-textual graphical techniques to render the molecular structures which the theories, hypotheses and concepts were ostensibly about. These techniques are now so entrenched that is difficult to imagine that we could talk, write, or even think about molecular structures without recourse to them. Thus, chemists have developed and adopted over time a number of techniques and conventions to depict -to visually represent -the three-dimensional structure of molecules on a two-dimensional graphic space. 2 Another related approach commonly adopted for the representation and investigation of molecular structures in chemistry has been that of physical molecular modeling, i.e., the representation, or rendering, of molecular structures through actual three-dimensional structures, commonly referred to as molecular models, or less commonly as physical models or structural models. This approach has been a constitutive practice of modem chemistry (Francoeur, "Forgotten Tool") and its origin can be traced as far back as its graphical counterpart (Ramsay, "Molecules" (I) and (II». The use of models was an integral part of the articulation of the chemists' knowledge and experience of molecular structures. In some sense the development and extension of what could be called "structural thinking" in chemistry (i.e. structural postulates, theories and concepts) has hinged at specific times upon the working and the sorting out of the geometrical and mechanical properties of physical molecular models (Francoeur, "Beyond").The practice of physical molecular modeling is, at the base, rather simple. It is the production and use of three-dimensional structures that depict, more or less to scale, the spatial position of atoms (or groups of atoms) in a given molecule, as well as the bonds between them. Most molecular models are assembled from commercially available modeling kits, which consist generally of modular elements (atomic units, or species, and connectors) from which a vast number of different structures can be assembled.

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L’article analyse le déroulement, aux États-Unis entre 1982 et 1990, de la controverse entourant la régulation des largages d’organismes génétiquement modifiés (OGM) dans l’environnement. Plus précisément, il se donne comme objet l’interaction entre trois ordres de pratiques : i) les événements suscités par des acteurs collectifs se présentant comme les porte-parole des intérêts du public, ii) les formes et les actions de réglementation, et iii) l’activité scientifique en contexte de controverse et ses enjeux. Une telle approche nous permet de dépasser la dichotomie simpliste d’une science rationnelle assaillie par un public irrationnel, ou, vice versa, d’une science corrompue manipulant cyniquement l’opinion publique sous le couvert d’argumentations techniques. Ce tableau simpliste doit être remplacé par celui d’un espace controversiste fondé sur l’existence d’institutions de régulation qui entretiennent à leur tour des relations complexes avec des institutions scientifiques de taille, composition et stabilité variables, depuis les associations professionnelles inscrites dans une durée moyenne jusqu’aux sous-disciplines et aux fronts de recherche à caractère relativement éphémère. Le « public », au terme de notre analyse, ne peut apparaître que comme un artefact construit par les acteurs en interactions, dans les interstices et à l’intérieur des terrains de juridiction des agences de réglementation.This article analyzes the unfolding of the controversy over the regulation of the release into the environment of genetically modified organisms (GMOs) in the United States between 1982 and 1990. More precisely, it looks at the interaction between three related sets of practices: i) the events provoked by collective actors presenting themselves as spokespersons for public interest groups, ii) regulatory forms and actions, and, iii) scientific activities and issues in moments of controversy. In doing so, the article goes beyond simplistic dichotomies such as those opposing a rational science to an irrational public, or the equally simplistic picture of corrupt scientists cynically manipulating public opinion by resorting to technical arguments. These simplifications need to be replaced by an analysis which equates controversies to socio-technical episodes grounded in the existence of regulatory agencies maintaining complex relations with scientific intitutions of varying size, scale, and composition, from long-lasting professional organizations to short-lived speciality fields and research fronts. In this perspective, the "public" proves to be an artifact constructed by contending actors in the interstices, and within the jurisdictional terrain, of various regulatory agencies.El artículo analiza el desarrollo, en los Estados Unidos entre 1982 y 1990, de la controversia sobre la regulación de la liberación de organismos genéticamente modificados (OGM) en el medio ambiente. Más precisamente, éste se da como objeto la interacción entre tres órdenes de prácticas: i) los acontecimientos provocados por los actores colectivos...