Roentgen (unit) absorbed dose in a wide range of matter. When measuring absorbed dose in a human due to external exposure, the SI unit the gray, or the related non-SI rad are used. From these can be developed the dose equivalents to consider biological effects from differing radiation types and target materials. These are equivalent dose, and effective dose for which the SI unit sievert or the non-SI rem are used. The following table shows radiation quantities in SI and non-SI units: Roentgen (unit) The roentgen or röntgen () (symbol R) is a legacy unit of measurement for the exposure of X-rays
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