How to make a collection of batteries out of only one battery? We will need a glass and a rectangular aquarium.

A battery in a glass full of water seems to be wider. In order to make it thinner we have to place an empty glass with a battery inside to an aquarium filled with water. Isn't that simple?

The ability of an optical apparatus to magnify depends not only on the shape and the material of the object, but also on the medium in which the apparatus operates. Your eye works properly in the air, but in water the image is blurred - the lens of the eye cannot focus well enough.

The air bubbles in this glass ashtray work like a reducing lens.

This toy serves the purpose of illustrating how our perception of objects (batteries) of the same size can change depending on the way in which we view them. Cylindrical glasses placed in aquarium have biconvex lens properties. All three glasses used here have the same shape. In order to obtain different images created by glass-turned-lenses their refraction index in relation to their surroundings is manipulated. By filling the glass with water we obtain a magnified image. On the other had, the size of the image is reduced if we fill aquarium with water an the glass remains empty. This is the same with the face of the girl in "Scuba-doo" drive under water.

A general lens equation is a combination of the values of the lens curve radius and various refractive idices of two different media on both sides of the lens.

n₁/p + n₃/q = (n₂ - n₃)/R₂ + (n₂ - n₁)/R₁.

The experiment presented above proves that convex lens is not always a focusing one and a concave lens is not always a dispersing one.