A Description of Helioscopes, and Some Other Instruments

...much. I am not very concerned with preventing a small amount of warping, as it does not create any noticeable error original: "sensible errour".

If it is desired to make the screw smaller, and only long enough to span original: "subtend" one whole degree—which is sufficient for instruments with a fifty or sixty-foot radius—it can be done very well with a straight screw if care is used. This will very accurately measure diameters and transits the passage of a celestial body across a telescope's field of view or a meridian to a single second.

Another thing I promised to explain further was the design of the arms and joint mentioned on page 73, as a universal instrument for drawing all types of dials sundials. This is used for:
1. Adjusting the hand of a clock so that it moves within the shadow of the style original: "Stile"; the gnomon or blade of a sundial of a dial (that is, in the plane of the right ascension of any point of the ecliptic or the heavens);
2. In the shadow of a perpendicular or inclined style;
3. For dividing and drawing all types of ellipses in any analemmatic projection a method of projecting the sphere onto a plane, often used for specific types of sundials;
4. And also for making all types of elliptical dials in Mr. Foster's Samuel Foster (d. 1652), a mathematician famous for his work on horizontal and elliptical sundials way.
5. Finally, it is used for communicating a circular motion through any irregularly bent path without shaking or variation, and similar tasks.

First, the instrument for drawing all types of dials by the tangent projection must be made in the manner described in the 11th Figure. In this figure, there are two axes or wire rods joined together by a joint which, because of its ability to adapt to all kinds of motions and bends, I call a Universal Joint this is a significant historical naming of what we now call a U-joint or Hooke's joint.

One of these rods (b b) is placed perpendicularly over the center of the dial by the help of a frame (a a). Its sharp or pointed end (c) is sunk into the center, around which it is moved according to the guidance of the second rod or axis (d d). This second rod or axis is to be moved and set by its frame so that it is parallel to the axis of the world the Earth's axis of rotation. Then, when the hand (e e) of this second rod is turned to the hour of twelve on the plate (f f), the hand of the first rod (g g) will point out the meridian or twelve o'clock line on the dial-plane.

And so, to draw any kind of dial, you have nothing to do but find the substyle the line on the dial plate directly beneath the gnomon and the altitude of the style above the plane, and then place the axis in its proper position accordingly—that is, parallel to the axis of the earth—and