When iron is to be quickened by the stone, let it be clean and bright, disfigured by no rust or dirt, and of the best steel[[216]]. Let the stone itself be wiped dry, and let it not be damp with any moisture, but let it be filed gently with some smooth piece of iron. But the hitting of the stone with a hammer is of no advantage. By these means let their bare surfaces be joined, and let them be rubbed, so that they may come together more firmly; not so that the material substance of the stone being joined to the iron may cleave to it, but they are rubbed gently together with friction, and (useless parts being rubbed off) they are intimately united; whence a more notable
BOOK FOURTH.
[CHAP. I].
ON VARIATION.
