A book or pile of books. Make the height of the pile around two thirds the width of the bottle.
A small object. Choose an object smaller than the pile of books. I used a paper swan.
A table
Water
What to do
Fill the bottle with water and put the lid on it. Try to make sure there is absolutely no air in the bottle (it may help to put the lid on underwater)
Place the book on the table
Place the object on the table about 15 cm behind the book.
Lean over so the book is at eye level and look over the top of the book. You should not be able to see the object on the other side.
Place the bottle on its side just behind the book.
Look over the top of the book again. You should be able to see the object on the table through the bottle, although it may be upside down. If you can't, move the object closer or further away until you can.
What's happening?
You can see the object because the water bends the light from the object around the books. When light hits a boundary between two substances, like the surface of water, it often bends. This is called refraction. In the case of water and air, when light goes from water into the air, it bends towards the surface of the water. You may also have found that the object was magnified by the bottle, because of the shape of the bottle.
The water in the bottle bends the light so it can be seen over the book.
In the atmosphere, light can bend when it hits a boundary between hot air and cold air. If it hits the boundary at a shallow enough angle, it can even be reflected. This bending or reflecting of light in the atmosphere is how mirages are formed. The bending of light isn't as great as when light goes from air to water, but on a large scale it can make a distant object appear much closer than they really are, or even to float upside down in mid-air.
Exactly how a mirage forms depends of the conditions of the atmosphere, especially the shape of the boundary between the hot and cold layers of air.
If there is a layer of cold air near the ground, with a layer of warm air above it, light from objects over the horizon can be bent so they appear to be closer than they really are, appear to float upside down in mid-air or both. This sort of mirage is most commonly seen at sea.
There is another type of mirage, which is caused by hot air near the ground with cooler air above it. Light approaching the ground at a shallow angle can be reflected from the hot air. You may have seen this on a roadway on a hot day. The light from the sky reflected off the road can make it look like there is water on the road. This sort of mirage is often seen in deserts as well.
More complicated images can be formed if there are several layers of air at different temperatures. Some mirages can look like towering castles which move and change as you watch.
Set the things up on the table like this.
Without the bottle, the object is hidden behind the book.
