The sympathetic powder, supposed to possess a healing influence
from a distance. The mediæval philosophers were very fond of calling
books, drugs, etc., connected with alchemy and astrology by
the term hermetic, out of compliment to Hermes Trismegistus. (
For by his side a pouch he wore Replete with strange hermetic powder, That wounds nine miles point-blank would solder.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894