Molecular model. Computer model of the molecular structure of a crystal, used to demonstrate ideas on perspective. This is a regular array (crystal) of three atoms (red, green, blue). Looking through the interior of the crystal, the views are often blocked after a short distance. A different view is seen along the surfaces or at lower centre. The perspective adopted allows long unobstructed views between rows of atoms. This is called the orchard effect. Important aspects of number theory, such as the distinction between rational and irrational numbers, emerges from such models. There is also a pattern in the surface colours. This model was created as an artwork by Professor Eric Heller.