Roentgen (unit) One roentgen deposits of absorbed dose in dry air, or in soft tissue. One roentgen of X-rays may deposit anywhere from in bone depending on the beam energy. This tissue-dependent conversion from kerma to absorbed dose is called the F-factor in radiotherapy contexts. The conversion depends on the ionizing energy of a reference medium, which is ambiguous in the latest NIST definition. The roentgen has its roots in the Villard unit defined in 1908 by the American Roentgen Ray Society as "the quantity of radiation which liberates by ionisation one esu of electricity per cm of air under normal conditions
Invention (musical composition) Bach adapted and modified the form to what is considered to be a formal invention. Bach wrote 15 inventions (BWV 772–786) as exercises for his son, Wilhelm Friedemann Bach. Bach later wrote a set of 15 three-part inventions, called sinfonias (BWV 787–801). Invention (musical composition) In music, an invention is a short composition (usually for a keyboard instrument) with two-part counterpoint. (Compositions in the same style as an invention but using three-part counterpoint are known as "sinfonias." Some modern publishers call them "three-part inventions" to avoid confusion with symphonies.) Well-known are the fifteen inventions that make up the first half