(542)
some other Impediments intervened (after it was come to hand), First on the Publisher's, then on the Engraver's side; the following Particulars concerning the same, promised some Months ago, had been imparted to the Publick a good while before this time: For the Draught of the Figures, representing the New Instrument it self, and the Description of the same, we are obliged to the ingenuity of Mr. Hook.
The first, second, and third Figures do represent the several parts of this Instrument; the fourth Figure, part of the Telescope, with the Instrument applied to it, and the fifth, the Rest, on which the whole reposeth.
The first Figure represents the brass Box with the whole Instrument, (excepting only the mooveable Cover) and the Screws, by which it is fixt to the Telescope. In this Figure (a a a a) is a small oblong brass Box, serving both to contain the Screws, and its Sockets or Female Screws, and also to make all the several moveable parts of the Instrument to move very true, smooth, and in a simple direct Motion. To one end hereof is screwed on a round Plate of Brass (b b b b) about 3 inches over; the extream Limb of whole outside is divided into 100 equal parts, and numbred by 10, 20, 30, &c. Through the middle of this Plate, and the middle of the Box (a a a) is placed a very curiously wrought Screw of about the bigness of a Goose Quill, and of the length of the Box, the head of which is by a fixed Ring or Shoulder on the inside, and a small springing Plate (d d) on the outside, so adapted to the Plate, that it is not in the least subject to shake. The other end of this Screw is by another little Screw (whose small point fills the Center or hole made in the end of the longer Screw for this purpose) render'd so fixt and steady in the Box, that there appears not the least danger of shaking. Upon the head of this Screw without the springing Plate, is put on a small Index (e e), and above that a Handle (m m) to turn the Screw round as often as there shall be occasion, without at all endangering the displacing of the Index, it being put on very stiff upon a Cylindrical part of the Head, and the Handle upon a Square. The Screw hath that third of it, which is next the Plate, bigger than
the
