Ibn al-Haytham was a scientist in the medieval Islamic world whose careful experiments with light and lenses laid the foundation for the modern science of optics. He insisted that ideas should be tested through experiments rather than simply accepted on authority, an approach that helped shape the scientific method used by scientists ever since. According to tradition, he wrote much of his seven-volume Book of Optics while feigning madness under house arrest, having pretended to be insane to avoid punishment after failing to deliver an impossible Nile flood-control project for Cairo's ruler — and the book went on to be studied by scholars in the Middle East and Europe for centuries.