Using Euclid in a practical context: Claude Richard’s course on sectors at the Jesuit Imperial College in 17th century Spain

This paper looks at two manuscripts kept at the Spanish Royal Academy of History (Madrid) containing the course on sectors that Professor Claude Richard taught at the Jesuit Imperial College in Madrid. The literary form of the course goes beyond practitioners’ commonplace books, for it aims at teaching practical geometry on a solid Euclidean basis while claiming that the entire practical geometry consists of the brief and easy use of pantometers, that is, Coignet-type sectors. Actually, the course focuses on checking the solid geometric foundations of the scales graduation, which would justify the numerical consideration of continuous magnitudes as quantities –accepting a margin of error sensorially imperceptible and irrelevant for the purposes of application