Rust is usually associated with decay. Professor Faraday, however, observes that, in some cases, it is curious to see how tin, a metal having a slight attraction for oxygen, protects other metals from oxidation or rust. In Canada, tin-plate is used for the roofs of houses, and you are dazzled by the lustre of the setting sun upon the roofs; whilst there, although it is exposed to the atmosphere year after year, it does not decay, because the superficial coat of oxide protects the tin and iron beneath.