If an Indian astrologer says your Moon is weak, the prescription is likely to be a pearl set in silver, worn on the little finger, first put on on a Monday.

Chandra's metal is silver, his gem is the pearl, his colour is white and his day is Monday, and the remedies follow from that list: fasting on Mondays, donating rice or milk, chanting the Chandra mantra. The logic is sympathetic rather than causal — like calls to like — and it is the same logic behind every planetary metal in European alchemy.