The story was current that Pope Leo X (1475–1521) had a precious stone, probably some type of “moonstone,”[676] which grew brighter as the moon waxed, exhibiting the soft, silvery brilliance of our satellite, and then gradually lost its brightness as the moon waned, growing paler and dimmer and becoming quite obscure as the moon’s disk ceased to be illumined by the sun. As a mate to this, Pope Clement VII (1475–1534) was reputed to have in his possession a stone with a golden spot which moved across the surface in exact accord with the apparent motion of the sun across the heavens from sunrise to sunset.[677] These are undoubtedly fables that were circulated intentionally, or more probably through pure love of exaggeration, in order to enhance the merit of two exceptionally fine specimens of moonstone and sunstone in the papal treasury. In the eighteenth century the collection of the Duke of Brunswick contained a magnificent ancient drinking-cup, of the kind used in sacrificial ceremonies, cut from a single piece of onyx; this cup was said to have formed part of the rich spoils taken from Mithridates by the Romans under Pompey. It was valued in the duke’s inventory at 150,000 thalers, and Catherine II of Russia is stated to have offered four times that sum, or 600,000 thalers ($400,000) for this unique cup.[678] In the symbolism of the Manichean sect, an early Christian heresy owing its origin to a direct and predominant influence of Persian ideas, pearls occupy a prominent place. A legendary or poetic pearl called “the bright moon” was the symbol of compassion, and one of the treatises ends with the words: “Our heart has received the majestic splendor of the pearl granting every wish.” We are also told of “a diamond pillar” which sustains humanity, and the Messenger of Light is likened to a perfumed mountain entirely composed of a mass of jewels.[679] The recital of two Arab travelers, Hasan ibn Vazid and Sulaiman, who visited India in the ninth century, contains a curious theory of the formation of pearls or rather of the pearl-oyster. The primal matter is assumed to be a gelatinous moss, analogous to that of a species of algæ. This floats upon the water and attaches itself to the keels of ships, where it hardens, develops a shell, and finally drops off to sink into the depths of the sea. The formation of the pearl itself is then discussed and the theory noted in Pliny’s Natural History and so often repeated after his time, namely, that pearls are formed from the “dew of heaven,” is cited; but the writer adds: “Others say that they [the pearls] are produced in the oysters themselves. This appears more probable and is confirmed by experience; for the greater part of those observed in the oysters are firmly attached there and are immovable. Those which are mobile are called by the merchants seed-pearls.” As a true Mohammedan the writer concludes with the pious ejaculation: “God knows how the matter really stands!”[680]