The Encyclopedia of Superstitions
The seventh son of a seventh son, or the seventh daughter of a seventh daughter, is commonly said to have magical gifts, particularly the gift of healing. This old and very widespread belief is sometimes stretched to include any seventh child of a family, whether the parent of the same sex was similarly born or not. More usually, however, the magical gifts are looked for only in the second generation of sevens. In some districts, it is thought necessary for the child's birth to be preceded by those of six brothers (or sisters) in an unbroken line, with no child of opposite sex intervening.
A person so born is, or was until very recently, believed to share with kings the power of curing the King's Evil, or scrofula, by touch. He or she can also cure goitre, ringworm, and the pain of burns in the same way. In the Scottish Highlands, a seventh son is said to have 'the power of the Magic Foot', which enables him to cure foot-troubles in others by placing his own foot on that of the sufferer. In most parts of Scotland, seventh children are credited with Second Sight and the ability to foretell the future. Almost everywhere, they are believed to make good doctors, quite apart from their power to heal certain diseases magically by touch.
Traditionally, the seventh child heals by laying his hand on the diseased part, sometimes, but not always, murmuring a secret prayer or charm as he does so. The rite is usually performed in the carly morning, while the healer is still fasting. In the early years of this century, a Somerset man cured scrofulous patients in the Brendon Hills district by touching, when thus fasting, on a Sunday morning, repeating at the same time certain words which no one was ever allowed to hear. He would not attempt a cure on any day but Sunday. Near Dulverton, at about the same period, a seventh daughter healed goitre by stroking the swelling.
Alexander Polson, in his Highland Heritage of Folklore (1926), records a more elaborate rite. The healer visited the sick person before breakfast on seven consecutive mornings, and washed the afflicted part with water drawn from a north-facing well. Here too, a secret incantation was used, and also spittle, for the seventh son spat in the water before it was applied. On the Isle of Lewis, after touching his patient, he hung a sixpence on a string round the latter's neck. If this was afterwards removed, the malady returned. The same belief attached to the gold angels formerly hung on white ribbons round the necks of people who had been touched for scrofula by the King.
The actual presence of the seventh child was not always necessary. It was believed that he could convey his healing powers to water, which could then be bottled and taken away. To do this, he first dropped a gold sovereign into the water, dipped his hand into it, and pronounced a blessing over it. If the patient was subsequently washed or sprinkled with the water so prepared, a cure was expected without any further rites.
Henderson mentions a Scottish Border belief which does not seem to be general in other parts of Britain. This was that the magical cures effected by a seventh child had to be paid for by a loss of his own vital energy. If he was required to perform such cures too often, he pined away and eventually died of exhaustion.
Text from The Encyclopedia of Superstitions, by E. and M.A. Radford, edited and revised by Christina Hole (Helicon Publishing, 1995)