 When a blind person employs a stick in order to learn about their surroundings, they do so via the pressure they receive in their hands when the stick encounters an object. This resistance or pressure is instantaneously transmitted from the end of the stick in contact with the object to the hand. Light, Descartes argues, is transmitted from the luminous objects to the eye in the same way: it is an instantaneous pressure exerted on the eye by the luminous object via the medium (e.g., air). The length of the stick or of the distance between the sun (or any other luminous object) and our eyes does not matter, so long as (1) the particles of matter between our hand and the end of the stick or our eye and the sun are continuous, and (2) the pressure coming from the end of the stick or the luminous object is sufficiently strong to affect our hand or eye, so that whatever happens at one end is instantaneously communicated to the other end (AT 7: 84, CSM 1: 153).