1911 Encyclopædia Britannica/Positive Organ
POSITIVE (or Portable) ORGAN, a medieval chamber organ which could be carried from place to place without being taken to pieces, and when played was placed on a table or stool and required a blower for the bellows, as well as a performer. It was larger and more cumbersome than the portative (q.v.), with which it has often been confounded. The positive had usually but one kind of pipe, the open diapason of 2 ft. tone, and in the 16th century the best types had three registers by means of which each note could be sounded with its fifth and octave, or each by itself, or again in combinations of twos. The positive differed from the regal in having flue pipes, whereas the latter had beating reeds in tiny pipes, one or two inches long, concealed behind the keyboard. During the early middle ages most of the pneumatic organs belonged to this type.
A well-known instance of an early positive or portable organ of the 4th century occurs on the obelisk erected to the memory of Theodosius the Great, on his death in A.D. 395. Among the illuminated manuscripts of the British Museum miniatures abound representing interesting varieties of the portable organ of the middle ages; such as Add. MS. 29902 (fol. 6) and Add. MS. 27695b (fol. 13), Cotton MS. Tiberius A VII. fol. 104d., all of the 14th century, Add. MS. 28962, Add. MS. 17280, both of the 15th century. These little organs were to be found at every kind of function, civil and religious; they were used in the dwellings and chapels of the rich; at banquets and court functions; in choirs and music schools; and in the small orchestras of Peri and Monteverdi at the dawn of the musical drama or opera.