A very good idea of the psaltery and dulcimer may be obtained from the xylophone. This instrument has bars of wood or metal which are struck with a wooden mallet. The keyboard was invented in the eleventh century. It was applied first to an instrument called a clavier and later to the organ. The first stringed instrument to which this new device was applied was the clavicytherium, or keyed cithara. It had a box with a cover and strings of cat-gut, arranged in the form of a half triangle. It was made to sound by means of a quill plectrum attached in a rude way to the end of the keys. This was the progress the piano of today had made in the thirteenth century. Next in order of development comes the monochord, clarichord, or clavichord, the latter being the name by which it is generally known. As it was the instrument most used during the six centuries which followed, it is worthy of close study. In shape it much resembled a small square piano without frame or legs. The strings were of brass, struck by a wedge made of the same metal which was called a tangent. It was capable of soft tones only, but they were very sweet and melancholy. The elder Bach loved this instrument. He did not take kindly to the piano which was about to supplant his beloved clavichord. One regrets that he could not have lived to have seen it perfected. In playing the music written by Bach we must remember that he wrote entirely for the clavichord. The instrument he used was, without doubt, the product of Italy, as during this time the Italians led all Europe in the arts. At a later period the clavichord was copied by the Germans and Belgians. It was used by them for centuries on account of its simple construction and low price. Mozart always carried one with him as part of his baggage when traveling. The virginal, spinet, and harpsichord followed the clavichord in rapid succession, considering that the last named instrument had been in favor for such a long time, with seemingly no attempt at improvement. All of these three instruments had strings of brass, with quill plectra attached to pieces of wood. These were called "jacks"--a name still used today in making up the action of the piano. [Illustration: Double Spinet or Virginal made by Ludovicus Grovvelus Flanders, 1600]