According to Julianus, a Spanish bishop who flourished in 450, the organ was in common use in churches at that time. In 822 an organ was sent to Charlemagne by the Caliph Haroun Alraschid, made by an Arabian maker. This instrument was placed in a church at Aix-la-Chapelle. There were good organ builders in Venice as early as 822, and before 900 there was an organ in the cathedral at Munich. In the ninth century organs had become common in England, and in the tenth the English prelate, St. Dunstan, erected one in Malmesbury Abbey, of which the pipes were of brass. The instruments of that time were extremely crude. [Illustration: Fig. 43. (From Franchinus Gaffurius, "_Theorica Musica_," Milan, 1492.)] From this time on there are many authentic remains in the way of treatises on organ building and description of organs. The essential elements of this instrument consist of pipes for producing sound, of which a complete set, one pipe for each key of the keyboard, is called a stop; bellows and wind chest for holding the wind, sliders or valves for admitting it to the pipes, and keys for controlling the valves. In his studies for a history of musical notation, Dr. Hugo Riemann quotes an extract from an anonymous manuscript of the tenth century, in which the author gives directions for a set of organ pipes. "Take first," he says, "ten pipes of a proper dimension and of equal length and size. Divide the first pipe into nine parts; eight of these will be the length of the second. Dividing the length of this again into nine parts, eight of these will be the proper length of the third; dividing the first pipe into four parts, three of them will be the length of the fourth; taking the first pipe as three parts, two of them will be the length of the fifth; eight-ninths of this again will give the proper length of the sixth; eight-ninths of this, the length of the seventh; one-half the first, the length of the eighth, or octave." This gives a major scale, with the Pythagorean third, consisting of two great steps, which was too sharp to be consonant. The semitone between the third and the fourth is too small, as is also that between the seventh and eighth. The modern way of making the pipes of smaller diameter as they become shorter, had evidently not been thought of. Nevertheless, these directions are very important, since they throw positive light upon the tuning of the various intervals, the pipe lengths and proportions affording accurate determinations of the musical relations intended. [Illustration: Fig. 44. PORTABLE ORGAN FROM THE PROCESSION IN HONOR OF MAXIMILIAN I. (From Praetorius' "_Syntagma Musica_," about 1500 A.D.)]