Page:History of the Royal Society.djvu/306

 lesser wheel, called the Spar-wheel, with strong Cogs, which in their motion round take hold of the round staves of another wheel of about the same diameter, set a little way above it, and fastned to the end of a beam of 15 or 16 foot long, laid parallel to the Horizon, with an iron gudgeon at the other end of it, to facilitate its motion round: This beam is called the round beam; out of it come a certain number of arms of about nine inches long, and three inches broad, which in their going round meet with other lesser arms (called Tapes) coming out of the Pestles (for so they call certain small quarters of Timber placed perpendicular to the Horizon, about nine foot long and four inches broad; they are set in a slight frame to keep them steady); by these small arms the Pestles are lifted up about two foot and a half, and then let fall into a strong wooden Trough set under them, wherein the Powder is put to be pounded.

'Every Mill hath two Troughs, and about sixteen Pestles: every Pestle hath fastned to the lower end of it a round piece of Lignum Vitæ, of about five inches long and three and a half diameter; and into the bottom of the Trough, just where the Pestle is to fall, is let in another piece of Lignum Vitæ, of the fashion and bigness of an ordinary Bowl, split according to its longest diameter: The Pestles are not lifted up all together, but alternatively, to make the Powder turn the better in the working; and for the same reason round Troughs are counted better than square.

'To make excellent Powder, it ought to be wrought thus thirty hours; but of late they will not afford it above eighteen or twenty hours; once Rh