Roentgen (unit) Roentgen (unit) The roentgen or röntgen () (symbol R) is a legacy unit of measurement for the exposure of X-rays and gamma rays. It is defined as the electric charge freed by such radiation in a specified volume of air divided by the mass of that air. In 1928 it was the first international measurement quantity for ionising radiation to be defined for radiation protection, and was an easily replicated method of measuring air ionization directly by using an ion chamber. It is named after the German physicist Wilhelm Röntgen, who discovered X-rays. Although relatively easy to measure, it had
The Invention of Art of human expression and embellishment. Reviewer Marc Spiegler called the book "a must-read for anyone active in the arts". The Invention of Art The Invention of Art: A Cultural History (2001) is an art history book by Dr. Larry Shiner (1934- ), Emeritus Professor of Philosophy, History, and Visual Arts at the University of Illinois, Springfield Shiner spent over a decade to finish the work of this book. The book sees fine art as a modern invention due to social transformations during the 18th century. David Clowney, writing for "Contemporary Aesthetics" summarizes the central thesis of this book. "In The