for using the third finger of the lower hand as a buttress finger, although only for three notes in the lower octave. (See also Renaissance structure.) Aurelio Virgiliano's "" ( 1600) presents ricercars intended for or playable on the recorder, a description of other musical instruments, and a fingering chart for a recorder in G4 similar to Jambe de Fer's. The Syntagma musicum (1614–20) of Michael Praetorius (1571–1621) in three volumes (a fourth was intended but never finished) is an encyclopaedic survey of music and musical instruments. Volume II, De Organographia (1619) is of particular interest for its description of no fewer than eight sizes of recorder ( or exilent in G5, discant in C5 or D5, alt in G4, tenor in C4, basset in F3, bass in B2, and in F2) as well as the four-holed . Praetorius was the first author to explain that recorders can confuse the ear into believing that they sound an octave lower than pitch, which phenomenon has more recently been explained in relation to the recorder's lack of high harmonics. He also shows the different "registers" of consort possible, 2′ (discant, alt, and tenor), 4′ (alt, tenor, and basset), and 8′ (tenor, basset, and bass) (see also Nomenclature). Additionally, he proposed cutting the recorder between the beak and the first finger hole to allow for a kind of tuning slide to raise or lower its pitch, similar to the Baroque practice of adjusting a recorder's pitch by "pulling out" the top joint of the recorder. The recorders described in Praetorius are of the "stretched hourglass" profile (see above, far right). He gives fingerings like those of Ganassi, and remarks that they normally have a range of an octave and a sixth, although exceptional players could extend that range by a fourth. "Double recorder" Some paintings from the fourteenth and fifteenth centuries depict musicians playing what appear to be two end-blown flutes simultaneously. In some cases, the two flutes are evidently disjoint, separate flutes of similar make, played angled away from each other, one pipe in each hand. In others, flutes of the same length have differing hand positions. In a final case, the pipes are parallel, in contact with each other, and differ in length. While the iconographic criteria for a recorder are typically a clearly recognisable labium and a double handed vertical playing technique, such criteria are not prescriptive, and it is