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 seven came to be recognised. Perhaps it was the regular appearance of the seven planets, visible to the naked eye, from which those early notions were based. Then the moon's phases consisted of four equal periods of seven days each. The seven stars in the Great Bear, the seven colours, the seven tones in music, the seven vowels in the Greek alphabet, the seven sages, and, naturally also, the seven known metals, were all evidences of this order of the universe. Out of this correspondence grew the Chaldean and Persian ideas of seven heavens, each with its gate of a different metal; the first of lead, the second of tin, the third of brass, the fourth of iron, the fifth of a copper alloy, the sixth of silver, and the seventh of gold.

The philosophers of Chaldea attributed to the heavenly bodies, or rather to the deities who had made these their homes, extensive control over the products of the earth. The sun-god produced gold, the moon-god silver, and so forth; and this view was prevalent certainly until the sixteenth century. Naturally all the early investigators had to picture their fancies more or less crudely, and thus alphabets originated. The Egyptian ideograms are the most familiar of this ancient poetry to us, and among these are some which are intelligible to us to-day. The sun and gold,, are still represented by that sign; water,, was so indicated in the papyri and in the alchemical books of three or four hundred years ago; and the sign still used for the planet and the metal mercury,, differs but little from the hieroglyph of Thoth, whom the Greeks called Hermes and the Romans Mercury. Greek students have imagined that this sign was derived from the caduceus or winged staff of the god, but some Egyptologists have claimed it as a picture of the "sacred ibis."