Snell’s Window

underwater mark tipple

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



Fear of falling

Photo by Mark Tipple

Photo by Mark Tipple

One of my pupils told me that the reason she found it difficult to learn to swim was that she had a fear of gaps. She said she did not like stepping from the platform to the train, or even crossing bridges and that being in water made her feel the same way.  She told me she could float and was not afraid to put her face in the water but it was the moment of taking her feet off the bottom of the pool that scared her.  She said that the moment of launching herself into the water is like the moment when you are falling asleep and you feel yourself fall off the edge of something, the moment when you suddenly jerk back to wakefulness. One man told me that his father had dangled him over a bridge when he was a child and he had been afraid of water ever since. He is learning to swim now, fifty years later, and doing well.

I think for many people fear of water is like a fear of falling, of being unsupported and many  people are able to swim as long as they are touching me. Even if I just touch them lightly with the finger of one hand they can swim, but as soon as I move my hand they panic.  One lady could swim if we swam together, with both of us swimming and me holding her hand, but even though I was not supporting her at all, she could not swim if I let go of her.  And many people can swim if I help them to start off, if I manage to get them over the falling moment when the ground disappears from under their feet.

All this has shown me how deeply psychological the fear of water and fear of swimming can be. It is therefore not surprising that once people start to overcome their fear of water, they sometimes find that other fears become less too; like the man who told me that once he had stopped being afraid of the water he also found that he had stopped being afraid of dogs.

It is interesting to watch people lose their fear. It doesn’t happen immediately of course but as long as the person keeps coming to the lessons the fear always goes, it just sort of floats away. I believe this is because the fear sits in a very deep and instinctual part of the memory or experience and is not really connected to the present situation. In a heated swimming pool, where they are never out of their depth and where I am there to help and support them, most people learn to swim.

Watching people overcome this fear has got me thinking about the nature of fear itself and how many of us are limited by fears that are not based in reality.