The virtual assistant in iOS can do all kinds of stuff, of course. But here are the 16 things we think everyone should try at least once.
In most vertebrates and some molluscs, the eye works by allowing light to enter and project onto a light-sensitive panel of cells, known as the retina, at the rear of the eye. The cone cells (for colour) and the rod cells (for low-light contrasts) in the retina detect and convert light into neural signals for vision.
Our eyes are detectors which are designed to detect visible light waves (or visible radiation). Visible light is one of the few types of radiation that can penetrate our atmosphere and be detected on the Earth's surface. As we have seen from the section on the discovery of infrared, there are forms of light (or radiation) which we cannot see.