subdivided into minutes, so that putting the cross of the threads in E
upon any part of this divided line, I presently knew what Angle the two
Rules AB and EF made with each other, and by turning the Screw in H, I
could fix them in any position. The other Ruler also RS was made much
after the same manner, only it was not fixt to the hollow cylindrical
Box, but, by means of two small brass Armes or Ears, it mov'd on the
Centers of it; this also, by means of the cross threads in the hole S,
and by a Screw in K, could be fastned on any division of another line
of cords of the same radius drawn on NO. And so by that means, the
Angle made by the two Rulers, AB and RS, was also known. The Brass box
CC in the middle was shap'd very much like the Figure X, that is, it
was a cylindrical Box stopp'd close at either end, off of which a part
both of the sides and bottomes was cut out, so that the Box, when the
Pipe and that was joyned to it, would contain the Water when fill'd
half full, and would likewise, without running over, indure to be
inclin'd to an Angle, equal to that of the greatest refraction of
Water, and no more, without running over. The Ruler EF was fixt very
fast to the Pipe V, so that the Pipe V directed the length of the Ruler
EF, and the Box and Ruler were mov'd on the Pin TT, so as to make any
desirable Angle with the Ruler AB. The bottom of this Pipe V was stop'd
with a small piece of exactly plain Glass, which was plac'd exactly
perpendicular to the Line of direction, or _Axis_ of the Ruler EF. The
Pins also TT were drill'd with small holes through the _Axis_, and
through those holes was stretcht and fastned a small Wire. There was
likewise a small Pipe of Tin loosly put on upon the end of V, and
reaching down to the sight G; the use of which was only to keep any
false Rayes of light from passing through the bottom of V, and only
admitting such to pass as pierced through the sight G: All things being
placed together in the manner describ'd in the Figure; that is, the
Ruler AB being fixt perpendicular, I fill'd the Box CC with Water, or