The piano, like all our contemporaneous musical instruments, is the result of a long development. Its fundamental principle is the setting of a stretched string in vibration by a blow, the vibrations acting upon the air so as to produce sound. A subsidiary principle (subsidiary because common to all stringed instruments, such as violins, harps, or guitars) is the shortening or lengthening of a string in order to obtain a higher or a lower note. In the piano, the application of this principle gives us a number of strings of different lengths. In the violin we have only four strings, but the length of the vibrating part is altered by pressing down the strings at different points with the fingers of the left hand. Before the idea of setting strings in vibration with a bow was conceived, they were plucked with the fingers, as in the case of the harp and the guitar, and it is probable that this is the oldest method of causing strings to sound. The Hebrew _kinnor_, the first musical instrument mentioned in the Bible (called "harp," Genesis iv. 21), was either a lyre or a small harp, and, according to Josephus, it was played with a plectrum, a small piece of ivory or steel, used to pluck the strings. Egyptian pictures of great antiquity show players using their fingers upon harp strings. At the same time the Egyptians were well acquainted with the principle of dividing a string by pressing upon it with the fingers of the left hand, as is proved by their pictures of lute players. But the use of a blow to set a string in vibration was also known in very early times. The instrument called a dulcimer, which is always seen now in Hungarian orchestras, is almost as old as the harp. It consists of a number of strings stretched across a shallow box, which acts as a resonator, and set in vibration by two little hammers in the hands of the player. It was this instrument which suggested the hammer action, and it is this action which makes the fundamental difference between the piano and its immediate precursors. An instrument similar to the dulcimer was the citole, the chief difference being that the strings were plucked with the fingers. Add the principle of stopping the strings with the fingers of the left hand, and the citole becomes the zither. In Lydgate's "Reson and Sensualité" (circa 1430) "cytolys" are enumerated among other instruments.