Answer:
Glass is the most common material used to construct lens elements, due to its good optical properties and resistance to scratching. Other materials are also used, such as quartz glass, fluorite, plastics like acrylic (Plexiglass), and even germanium and meteoritic glass.
Organum added a new note to the gregorian chants to enhance harmony
Let's say that there is a piece of music in the key of C. (No flats, no sharps, all natural.) If in front of the note there is a flat or sharp, you play what is shown and they are called an <u>accidentals</u>.
