Note:  Do not rely on this information. It is very old.

I

I, 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.