Exercise ball standard exercises, such as a push-up, on an unstable surface can be used to increase activation of core trunk stabilizers and in turn provide increased trunk strength and greater resistance to injury. Fitness Experts and some doctors also recommend sitting on an exercise ball instead of an office chair. That is based on the theory that the abdominal and back muscles are constantly engaged and active to maintain proper posture and balance on the ball. There is no scientific evidence of those benefits occurring by just sitting without additional exercises. However, some people warn against using a Swiss ball as
Crystal ball ball that is brought into full sunlight. The image of the sun formed by a large crystal ball will burn a hand that is holding it, and can ignite dark-coloured flammable material placed near it. Ball lenses such as are used to couple fiber optics are identical to crystal balls, but in tiny form, commonly 1mm to 10mm in diameter. A crystal ball lies in the Sceptre of Scotland that is said to have been originally possessed by pagan druids. Philadelphia's University of Pennsylvania Museum of Archaeology and Anthropology (also called "Penn Museum" for short) displays the third largest crystal