Newtonian telescope Newtonian telescope The Newtonian telescope, also called the Newtonian reflector or just the Newtonian, is a type of reflecting telescope invented by the English scientist Sir Isaac Newton (1642–1727), using a concave primary mirror and a flat diagonal secondary mirror. Newton's first reflecting telescope was completed in 1668 and is the earliest known functional reflecting telescope. The Newtonian telescope's simple design makes it very popular with amateur telescope makers. Newton's idea for a reflecting telescope was not new. Galileo Galilei and Giovanni Francesco Sagredo had discussed using a mirror as the image forming objective soon after the invention of the
Folk instrument Folk instrument A folk instrument is a musical instrument that developed among common people and usually does not have a known inventor. It can be made from wood, metal or other material. Such an instrument is played in performances of folk music. The instruments can be percussion instruments, or different types of flutes or trumpets, or string instruments that are plucked, hammered or use a form of bow. Some instruments are referred to as folk instruments because they commonly appear in folk music, even though they do not meet the criteria defining a folk instrument; an example is the harmonica.