of the garden. It is made of clay, which has been stained by age with subtle brown and orange tones. In 1977, the tile roof of the wall was restored with tree bark to its original appearance. When the garden was rebuilt in 1799, it came up higher than before and a view over the wall to the mountain scenery behind came about. At present this view is blocked by trees. The garden had particular significance for the composer John Cage, who composed a series of works and made visual art works based on it. Meaning of the garden Like any work of art, the artistic garden of Ryōan-ji is also open to interpretation or research into possible meanings. Many different theories have been put forward inside and outside Japan about what the garden is supposed to represent, from islands in a stream, a tiger family crossing a river, mountain peaks, to theories about secrets of geometry or the rules of equilibrium of odd numbers. Garden historian Gunter Nitschke wrote: "The garden at Ryōan-ji does not symbolize anything, or more precisely, to avoid any misunderstanding, the garden of Ryōan-ji does not symbolize, nor does it have the value of reproducing a natural beauty that one can find in the real or mythical world. I consider it to be an abstract composition of 'natural' objects in space, a composition whose function is to incite meditation." Scientific analysis of the garden In an article published by the science journal Nature, Gert van Tonder and Michael Lyons analyze the rock garden by generating a model of shape analysis (medial axis) in early visual processing. Using this model, they show that the empty space of the garden is implicitly structured, and is aligned with the temple's architecture. According to the researchers, one critical axis of symmetry passes close to the centre of the main hall, which is the traditionally preferred viewing point. In essence, viewing the placement of the stones from a sightline along this point brings a shape from nature (a dichotomously branched tree with a mean branch length decreasing monotonically from the trunk to the tertiary level) in relief. The researchers propose that the implicit structure of the garden is designed to appeal to the viewer's unconscious visual sensitivity to axial-symmetry skeletons of stimulus shapes. In support of their findings, they found that imposing a random perturbation of the locations of individual