The early organs were furnished with slides which the organist pulled out when he wished to make a pipe speak, and pushed back to check its utterance. The date of the invention of the valve is uncertain, but it must have been about as soon as the power of the instrument was increased by the addition of the second or third stop. Before this, however, and perhaps for some little time after, there were many organs in use, which were committed to the diaphony of Hucbald, having in place of the diapason three ranks of pipes, speaking an octave and the fifth between. Each of these combined sounds was treated in the same way as simple ones are on other instruments, and if chords were attempted upon them the effect must have been hideous indeed; but it is probable that at this time the notes were played singly, and not in chords, or at most in octaves. We do not know the date at which this style of organ building ceased, but it is probably before the thirteenth century. There is a manuscript of the fourteenth century in the Royal Library at Madrid, stating that the clavier at that epoch comprised as many as thirty-one keys, and that the larger pipes were placed on one side, and small pipes in the center, the same as now. The earliest chromatic keyboards known are those in the organ erected at Halberstadt cathedral in 1361. This instrument had twenty-two keys, fourteen diatonics and eight chromatics, extending from B natural up to A; and twenty bellows blown by ten men. Its larger pipe B stood in front, and was thirty-one Brunswick feet in length and three and a half feet in circumference. This note would now be marked as a semitone below the C of thirty-two feet. In this organ for the first time a provision was made for using the soft stop independently of the loud one. This result was obtained by means of three keyboards. The keys were very wide, those of the upper and middle keyboards measuring four inches from center to center. The sharps and flats were about two and a half inches above the diatonic keys, and had a fall of about one and a quarter inches. The mechanical features of the organ were very greatly improved during the next century, but it was not until the old organ in the Church of St. AEgidien in Brunswick that the sharps and naturals were combined in one keyboard in the same manner as at present. The keys were still very large, the naturals of the great manual being about one and three-quarters inches in width. It was to the organ at Halberstadt that pedals were added in 1495, but no pipes were assigned to them. They merely pulled down the lower keys of the manual. [Illustration: Fig. 45. BELLOWS BAGS IN THE ORGAN AT HALBERSTADT, AND METHOD OF BLOWING. (Praetorius.)]