Many promoters of reforms on the teaching at the turn of the nineteenth and twentieth centuries insist on the experimental character of geometry, which was absent from Euclid’s Elements. In this context, our aim is to analyze epistemological functions of geometrical instruments, i.e. their roles as knowledge tools, their choices and their uses. For that, we highlight three ways of conceiving an experimental teaching in this period, from four arguments (mathematical, pedagogical, scientific and social) given to promote a new teaching of geometry and from textbooks of the time. We also show how the different functions of the instruments intervened in the answers given to the question of the transition from an experimental teaching to a theoretical teaching of geometry.