When you are under water and you look upwards, you see everything above the surface of the water through a round window of light. I think we are so used to this phenomenon, if not from experience then at least from films, that we don’t think about it. At least I didn’t until I saw Neil Gower’s beautiful drawing for the cover of the Watermarks anthology.

The round window of light is known as Snell’s Window and is to do with refraction of the light as it travels from the air to the water. The area outside of the cone of light that forms the window will be completely dark or will reflect objects within the water. It sounds complicated, and in terms of physics it is, but a photograph taken from under the water reminds us how familiar the effect is even if, like me, you don’t fully understand it.

Art work for Watermarks by Neil Gower, underwater photograph by Mark Tipple