What is a mirage? Have you ever looked along a smooth road in hot weather and seen what appears to be a stretch of water where none exists? This is a mirage. It is caused by the air being heated in such a way that hot layers of air lie under cold layers. The cold air is thicker than the hot air and this causes light passing trough the layers to be bent. This bending gives the illusion of water, or even sends a picture of the scene many miles away. Mirages often occur in the desert. Lakes are seen where there is really nothing but sand. And sometimes images of towns and palm trees appear and taunt the thirsty traveller. The same thing happens at sea, when ghostly ships are seen floating in the sky. It is easy to tell a mirage from the real thing, however, because the objects in it are all upside down. This is caused by the way the rays of light are bent.
How can ice burn you? The burning sensation you get when you touch something hot, say a hot poker, is caused by the effect of the heat on the nerve-endings in your fingers. These nerve endings flash a message to the brain, in the form of a stab of pain, that says something dangerous is happening to the fingers. The brain flashes a message back to tell the fingers to drop the poker. In the same way you can get a burning sensation by holding your hand against a block of ice. It is not so severe as the pain caused by something hot, but is very similar in feeling, and is caused by the body’s heat being suddenly taken away from the nerve-endings. The burning feeling lingers on in both cases because the sensitive nerve-endings have been damaged by the sudden change in temperature.