As disciplines, undergraduate physics and chemistry leverage a particularly wide range of semiotic systems (modes) in order to create and communicate their scientific meanings. Examples of the different semiotic systems employed are: spoken and written language, mathematics, chemical formulae, graphs, diagrams, sketches, computer simulations, hands-on work with experimental apparatus, computer simulations, etc. Individual semiotic resources within this range of semiotic systems are coordinated in specific constellations (Airey & Linder, 2009) in order to mediate scientific knowledge. In this Swedish Research Council project, we are interested in the representation of scientific phenomena that cannot be seen. The question we pose is: How is scientific knowledge mediated when we cannot directly interact with the phenomena in question through our senses? We adopt a social semiotic approach (Airey & Linder, 2017; van Leeuwen, 2005), to investigate the ways in which two phenomena—electromagnetic fields and chemical bonds—are presented in undergraduate textbooks. To do this we carried out a semiotic audit (Airey & Erikson, 2019) of eight textbooks (four in each discipline). We note that the individual resources used have a mixture of affordances—whilst the majority retain high disciplinary affordance, others are unpacked (Patron et al. 2021) providing higher pedagogical affordance. We discuss the ways in which the resources have been combined and orchestrated (Bezemer & Jewitt, 2010) in order to attempt to make visible that which is invisible, and identify a number of potential problems. In earlier work, Volkwyn et al. (2019) demonstrated how experimental work with physics devices can make the Earth’s magnetic field accessible to students through chains of transduction. Thus, we propose that encouraging transductions across the semiotic resource systems provided in textbooks may help students to experience the invisible. References Airey, J. (2006). Physics students' experiences of the disciplinary discourse encountered in lectures in English and Swedish (Licentiate dissertation, Department of Physics, Uppsala University). Airey, J. (2009). Science, language, and literacy: Case studies of learning in Swedish university physics (Doctoral dissertation, Acta Universitatis Upsaliensis). Airey, J. (2015). Social Semiotics in Higher Education: Examples from teaching and learning in undergraduate physics. In In: SACF Singapore-Sweden Excellence Seminars, Swedish Foundation for International Cooperation in Research in Higher Education (STINT) , 2015 (pp. 103). Airey, J., & Eriksson, U. (2019). Unpacking the Hertzsprung-Russell diagram: A social semiotic analysis of the disciplinary and pedagogical affordances of a central resource in astronomy. Designs for Learning, 11(1), 99-107. Goodwin, C. (2015). Professional vision. In Aufmerksamkeit: Geschichte-Theorie-Empirie (pp. 387-425). Wiesbaden: Springer Fachmedien Wiesbaden. O’Halloran, K. (2007). Mathematical and scientific forms of knowledge: A systemic functional multimodal grammatical approach. language, Knowledge and pedagogy: functional linguistic and sociological perspective, 205-236. Patron, E. (2022). Exploring the role that visual representations play when teaching and learning chemical bonding: An approach built on social semiotics and phenomenography(Doctoral dissertation, Linnaeus University Press).Making the invisible visible: The role of representations in teaching and learning university physics and chemistry