Note: Do not rely on this information. It is very old.
II, the ninth letter of our alphabet, was derived through the Greeks from the Phoenicians, and ultimately from the Egyptian hieroglyphics. Its original form somewhat resembled a z, which became a vertical stroke after the omission of the additional strokes forming the upper and lower angles. The proper sound of i is that which it has in machine - a sound which still belongs to it in most European languages, but which in English now gives its name to the letter e. This sound appears in a weakened form in the "short i" of bit, etc., which is the normal sound of the letter in English, whereas that from which it takes name occurs only when a final e or a guttural follows in the next syllable - e.g. bite, high.