A Description of Helioscopes, and Some Other Instruments

The arms are to be made so they can be inclined at any angle; that is, the axis of the connecting piece original: "Medium", which is held by the iron arms, can be tilted toward the axis of the rod on which they are mounted at any desired angle. Once set to that angle, it can be held steadily in place by a pin, screw, or wedge. The method I use for the Azimuth Instrument (described on page 73 of my Animadversions Robert Hooke’s 1674 work, Animadversions on the First Part of the Machina Coelestis) is illustrated and explained in Figure 9.

In this figure, G represents a brass socket that can move rotationally original: "cylindrically round" about the end or neck B of the axis or rod BB (the same as rod a b in Figure 22 of my Animadversions). This socket can be fixed in any desired position using a side-screw h, similar to those commonly used for most instruments mounted on a tripod original: "three-legged staff", which is often referred to as a "cylinder and socket." This brass socket has a small iron rod, k, fixed into its hollow interior original: "concave part" at point k. A small eyelet or hole is made through this rod, and by pushing a wedge-shaped pin m through that hole, the semicircular iron arms CC are kept steady and fixed in whatever position they have been adjusted to original: "rectified to".

The semicircular arms CC should be made of very high-quality iron, or preferably steel. One of them must have a channel or groove running through its middle along the entire length of a quadrant (a quarter-circle), specifically from n to o. This allows it to be adjusted to any point between n and o, depending on the specific requirements. It should also be noted that the iron rod k must be offset from the axis of the socket g by the same distance that n is from i (or o is from p, the midpoint of the iron arms between i and i). This ensures that, when necessary, the center hole or "hands" i can be moved to position p and fastened there.

A joint must be made at q in the semicircular arms so ⌞that when the end n of the arms is fixed at or near k, the other arm C can pivot back original: "fall back" from point i. Without this, the circular motion often could not continue for a full rotation or be transmitted from one rod to the other via the connecting plate original: "Medium or Plate" x. The individual pieces of this joint are shown separately in Figure 9, and you can see them assembled and ready for motion in Figure 10. Descriptions for every part are provided in the text, cross-referenced using letter markings original: "Literal marks".