Why do some old coffins have a glass window?

A short-lived practice in Victorian times was the glass viewing window in iron coffins. This example was a child's coffin, carved in wood, but with a metal lid. This allowed family and friends to view the deceased while keeping odors to a minimum, and the thought was to help prevent the spread of diseases like cholera by keeping the coffin closed. And since Victorians had an intense fear of being buried alive, the window was used as a warning system: it was believed that if breath condensation developed on the inside of the glass, it would notify family that the person had been accidentally "buried" alive.