In his various experiments, Ibn Al-Haitham used the term “"al-Bayt al-Muẓlim"”(), translated in English as dark room. In the experiment he undertook, in order to establish that light travels in time and with speed, he says: “If "the hole was covered with a curtain and the curtain was taken off, the light traveling from the hole to the opposite wall will consume time.”" He reiterated the same experience when he established that light travels in straight lines. The most revealing experiment which indeed introduced the camera obscura was in his studies of the half-moon shape of the sun’s image during eclipses which he observed on the wall opposite a small hole made in the window shutters. In his famous essay "On the form of the Eclipse" ("Maqālah fī Sura al-Kosūf") () he commented on his observation "The "image of the sun at the time of the eclipse, unless it is total, demonstrates that when its light passes through a narrow, round hole and is cast on a plane opposite to the hole it takes on the form of a moon-sickle"”.