=Mechanical Improvements=.—The pipes in the early organs were made of copper, lead, tin, silver, glass, ivory and various woods, but experiments finally showed =tin= or =wood= to be best suited for the purpose. The earliest organs had about twelve pipes, and the larger instruments three octaves, but without the chromatic intervals. The pipes were arranged according to the sequence of tones in the old Church modes, the _octave containing_ but _three semitones_: between E-F, A-B flat and B-C. The chromatic tones were added gradually, the breadth of the keys being correspondingly reduced as the increased number of keys occupied the same space as before. Heretofore, the _wind_ had usually been _forced from_ the _bellows_ by the _weight_ of men standing upon them, but in the 10th century use began to be made of a =lever=, the bellows presumably being weighted. =The Keyboard is Adopted=.—In the 11th century, the keyboard appeared, supplanting the levers and slides, previously in use. The first organ containing this marked improvement was made for the Cathedral at Magdeburg, Germany. It had sixteen keys. In 1350, a monk at Thorn built an organ with twenty-two keys, and in 1361 an organ was built for the Cathedral at Halberstadt with fourteen diatonic and eight chromatic tones in a compass extending from B, second line, bass staff, to A, second space, treble. This organ had three keyboards, now termed manuals. =The Pedals=.—The invention of pedals is variously ascribed to Albert Van Os (about 1120), to Van Valbeke, of Brabant, and to a German named =Bernhard= (1470), an organist of Venice. The latter probably improved, but did not invent the pedals. The pedals at first did not exceed the compass of an octave, and were used only for sustaining prolonged tones. They were _fastened_ to the broad _manual keys_ by stout cords, thus enabling the performer to draw down the desired key with the foot. About the year 1418 the pedals began to be attached to _independent pedal-pipes_, thus imparting to the organ a certain dignity and sonority, still a chief characteristic of the instrument. After 1475, all important organs were built with pedal keyboard. =The Introduction of Stops=.—Up to the 14th century, the different registers (set of pipes with uniform tone quality) could not be sounded separately, that is to say: _all_ the _pipes_ belonging to any one key _sounded_ when that key was depressed. At the close of the 14th century it was found possible to add =valves= to the pipes in such a manner as to cause the wind to pass through or be cut off from any series of pipes at will. The opening and closing was managed through a spring. The next improvement was to introduce a =slide= to open or close the passage of wind into the pipes. With these improvements it became possible for builders to set themselves to the improvement of the various “stops” or registers.