Complete reflection of a ray of light in a medium such as water or glass, from the surrounding surfaces back into the medium. It occurs when the angle of incidence is greater than a certain limiting angle, called the critical angle. In general, it takes place at the boundary between two transparent media when a ray of light in a medium of higher index of refraction approaches another medium of lower index of refraction at more than the critical angle. At all angles less than the critical angle, both reflection and refraction occur. Total internal reflection is responsible for rainbows, atmospheric halos, the sparkle of a diamond, and the path of light through optical fibres.
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Cross section showing one cylinder of a four-stroke internal-combustion engine. In the first stroke elipsis
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Medical specialty dealing with the entire patient rather than a particular organ system, covering diagnosis and medical (rather than surgical) treatment in adults. Its development began in the 17th century with Thomas Sydenham's concept of disease, but until disease-specific therapies were developed in the 20th century, internists could do little to treat diseases. As more specific treatments became available, medical knowledge increased, and subspecialties in specific organ systems were defined, internal medicine became recognized as a specialty.
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