But the story is from the False Decretals.
(231) See Rydberg, The Magic of the Middle Ages, translated by Edgren, pp.

63-66.
But highest in repute during centuries was the Agnus Dei--a piece of wax blessed by the Pope's own hand, and stamped with the well-known device representing the "Lamb of God." Its powers were so marvellous that Pope Urban V thought three of these cakes a fitting gift from himself to the Greek Emperor.

In the Latin doggerel recounting their virtues, their meteorological efficacy stands first, for especial stress is laid on their power of dispelling the thunder.

The stress thus laid by Pope Urban, as the infallible guide of Christendom, on the efficacy of this fetich, gave it great value throughout Europe, and the doggerel verses reciting its virtues sank deep into the popular mind.

It was considered a most potent means of dispelling hail, pestilence, storms, conflagrations, and enchantments; and this feeling was deepened by the rules and rites for its consecration.