Ice was originally thought to be slippery due to the pressure of an object coming into contact with the ice, melting a thin layer of the ice and allowing the object to glide across the surface.
For example, the blade of an ice skate, upon exerting pressure on the ice, would melt a thin layer, providing lubrication between the ice and the blade. This explanation, called "pressure melting", originated in the 19th century. It, however, did not account for skating on ice temperatures lower than −4.0 °C, which is often skated upon.