white paper

Ingredients

white paper

Preparation Steps

Original Recipe Text

The apparatus construction involves blocking six of seven cylindrical holes on the outside of a wooden half-cylinder and pasting white paper over them on the inside (p. 171). The paper is firmly pressed with a finger to reveal the round rim of the hole, and the center of each opening is then marked with a fine pen (p. 171). This paper serves as a screen for observing reflected sunlight (p. 171).

Evidence

"six of the seven holes are blocked on the outside of the half-cylinder and pasted over on the inside with a piece of white paper. This is firmly pressed with a finger until the round rim can be seen and the centre of the opening can be marked with a fine pen."

Remarks

In the reflection apparatus (ālat al-in‘ikās) described by Ibn al-Haytham (d. 1041), white paper is used as a projection screen for sunlight reflected from various mirrors (plane, spherical, cylindrical, and conic) (p. 171). The paper screen allows the person conducting the experiment to see the reflected light and confirm that it forms an equilateral triangle with the entry hole and the brass plate's tip (p. 171).