The next stage was to make vents or holes in the pipe, arranged so that they could easily be covered by the fingers, and as the sound always escaped by the hole nearest the reed, it was easy to produce a series of sounds by removing one or more fingers in succession. In a somewhat similar way, a series of sounds were obtained from the vibrations of a single cord by pressing, or merely touching, it at certain points, and thus shortening the portion which was allowed to vibrate. The primary object of all music is to give pleasure through the ear by imitating, or reproducing, more or less correctly, the sound of the human voice, and other natural sounds, so we find that as early instruments began to be improved they were so constructed as to produce various notes having the same intervals between them as are found between the tones of the human voice. In this way instruments with a fixed scale were obtained, and we know that in course of time various nations improved the instruments they had in use, the ancient Greeks especially bringing the art of music and their favourite stringed instrument, the lyre, to a high degree of perfection. The great defect of all the more ancient instruments was their limited compass, most of them containing from five to ten notes only, thus rendering it impossible to play anything upon them except by the same series of notes and at the same pitch. This was gradually remedied, both as regards wind and stringed instruments, by adopting various devices whereby their compass was extended, and by introducing, with more or less accuracy, new notes called semi-tones between the original notes. The modern method of tuning musical instruments by “equal temperament” was unknown until the time of Johann Sebastian Bach (1685–1750) who, disregarding the custom which had prevailed until his day, of writing in a few keys only, and tuning instruments so as to render these keys nearly perfect at the expense of the rest, himself tuned the instruments on which he played in “equal temperament.” When he first began to play music on the harpsicord, tuned in the old way, in other than the keys in which it was originally composed, the effect was almost unbearable, and it thus became necessary to alter the relation of the notes throughout the whole scale by framing a complete chromatic scale having exactly the same interval between each semi-tone. In this way every note was slightly altered from the true natural scale, but not to such an extent as to seriously offend the ear.