A popular notion has long been current, more especially on the shores
of the Mediterranean, that if a magnetic rod be rubbed with an onion,
or brought in contact with the emanations of the plant, the directive
force will be diminished, while a compass thus treated will mislead the
steersman. It is difficult to conceive what could have given rise to so
singular a popular error.[47]--_Humboldt’s Cosmos_, vol. v.