Carl Linnaeus, The Lapland Journey, translated by Peter Graves (Edinburgh: Lockharton Press, 1995), p. 40.
Hälsingland, 15/05/1732, ¶116:
Wherever there was a river, there was a wheel driving a hammer for pounding flax; they are designed in such a way that a trapdoor in the floor can be raised in order to stop them.