The contrivance of the Engine is, only to make the ends of two large _Mandrils_ so to move, that the Centers of them may be at any convenient distance asunder, and that the _Axis_ of the _Mandrils_ lying both in the same plain produc’d, may meet each other in any assignable Angle; both which requisites may be very well perform’d by the Engine describ’d in the third Figure of the first _Scheme_: where AB signifies the Beam of a Lath fixt perpendicularly or Horizontally, CD the two Poppet heads, fixt at about two foot distance, EF an Iron _Mandril_, whose tapering neck F runs in an adapted tapering brass Collar; the other end E runs on the point of a Screw G; in a convenient place of this is fastned H a pully Wheel, and into the end of it, that comes through the Poppet head C, is screwed a Ring of a hollow _Cylinder_ K, or some other conveniently shap’d Tool, of what wideness shall be thought most proper for the cize of Glasses, about which it is to be imploy’d: As, for Object glasses, between twelve foot and an hundred foot long, the Ring may be about six inches over, or indeed somewhat more for those longer Glasses. It would be convenient also, and not very chargeable, to have four or five several Tools; as one for all Glasses between an inch and a foot, one for all Glasses between a foot and ten foot long, another for all between ten and an hundred, a fourth for all between a hundred and a thousand foot long; and if Curiosity shall ever proceed so far, one for all lengths between a thousand and ten thousand foot long; for indeed the principle is such, that supposing the _Mandrils_ well made, and of a good length, and supposing great care be used in working and polishing them, I see no reason, but that a Glass of a thousand, nay of ten thousand foot long, may be as well made as one of ten; for the reason is the same, supposing the _Mandrils_ and Tools be made sufficiently strong, so that they cannot bend; and supposing the Glass, out of which they are wrought, be capable of so great a regularity in its parts as to refraction: this hollow _Cylinder_ K is to contain the Sand, and by being drove round very quick to and fro by means of a small Wheel, which may be mov’d with ones foot, serves to grind the Glass: The other _Mandril_ is shap’d like this, but it has an even neck instead of a taper one, and runs in a Collar, that by the help of a Screw and a joynt made like M in the Figure, it can be still adjustned to the wearing or wasting neck: into the end of this _Mandril_ is screwed a Chock N on which with Cement or Glew is fastned the piece of Glass Q that is to be form’d; the middle of which Glass is to be plac’d just on the edge of the Ring, and the Lath OP is to be set and fixt (by means of certain pieces and screws, the manner whereof will be sufficiently evidenc’d by the Figure)