The mechanism of vision: the path of light through the human eye in Portuguese textbooks of natural sciences (1900-1950)

Resumen

Following the celebration of the International Year of Light (2015), the main objective of this article is to show how vision was presented in the curriculum and in natural science textbooks published in the first half of the 20th century in Portugal. For this purpose, a qualitative method based on the Chevallard’s concept of didactic transposition was used. The content of the natural sciences curriculum showed that the study of vision was always associated to the study of sense organs. The anatomical description of the sense of vision was organized mainly around the eyeball and organs that are accessory to the eye. The analysis of textbooks showed that the didactic transposition of scientific knowledge about vision was based in detailed descriptions of the membranes and humors of the eye, of accessory organs and of the constitution and functioning of the lacrimal mechanism. The authors also showed a profound knowledge of the mechanism of vision, explaining clearly the path taken by light from the eyeball to the retina, leading to the formation of images. The textbooks published in the two first decades of the 20th century offered more complete accounts of these organs and the vision mechanism than those published between the 30’s and the 50’s