Black spirits and white,
Blue spirits and grey,
Mingle, mingle, mingle,
You that mingle say_.

And in a former part,

--_weyward sisters, hand in hand,--
Thus do go about, about.
Thrice to thine, and thrice to mine.
And thrice again to make up nine!_

These two passages I have brought together, because they both seem
subject to the objection of too much levity for the solemnity of
enchantment, and may both be shewn, by one quotation from Camden's
account of Ireland, to be founded upon a practice really observed by the
uncivilised natives of that country: "When any one gets a fall, _says
the informer of Camden_, he starts up, and, _turning three times to the
right_, digs a hole in the earth; for they imagine that there is a
spirit in the ground, and if he falls sick in two or three days, they
send one of their women that is skilled in that way to the place, where
she says, I call thee from the east, west, north, and south, from the
groves, the woods, the rivers, and the fens, from the fairies _red,
black, white_." There was likewise a book written before the time of
Shakespeare, describing, amongst other properties, the _colours_ of
spirits.

Many other circumstances might be particularised, in which Shakespeare
has shown his judgment and his knowledge.