A Description of Helioscopes, and Some Other Instruments

These Lines found in this way are the true azimuth lines Azimuth refers to the horizontal angle or direction of a celestial body of the points or divisions of that parallel A circle of latitude or declination on the celestial sphere. They are traced out exactly in this manner without any difficulty of calculation. For certain purposes in surveying, navigation, and so on, these are of very great use, as I shall show later.

The universal application of this invention original: "Contrivance" for resolving almost all spherical questions Problems involving spherical trigonometry, essential for plotting courses at sea makes it very useful in navigation, provided it is adapted as it should be. This is especially true for the common sailor's use; with only a very few rules, a sailor will be able to immediately find the hour and azimuth of any point in the heavens with enough accuracy for most observations that can be made at sea, which I will discuss more hereafter.

To make the hand or pointer original: "Index" of a clock move along with the shadow of the style The part of a sundial that casts the shadow on the face of a sundial exposed to the sun, this joint The universal joint is used. By using it to connect the axle original: "arbor" of the wheel that rotates every twenty-four hours to the axle of the clock hand, the motion is achieved without any other wheel or pinion A small gear in the dial or face of the clock.

If the axle of the clock (which would normally carry the hand around in twenty-four hours) is set at the same inclination to the plane of the dial as the Earth's axis—whether it is parallel to the axis or not, it does not matter at all—the hand will work if it is adjusted correctly. The style of the sundial must rise from the center of the dial, through which the axle is extended to carry the hand, and be placed in its parallel position relative to the Earth's axis, as is required for a tangent dial A sundial where the hour lines are determined by the geometric tangent of the sun's angle.

The shadow-line of the axis upon the plane of the dial is always carried around the center of a dial in a plane that passes through the axis or style. This shadow moves in equal increments of time around the axis, but it creates unequal movements across the flat surface of the dial, depending on the angle of inclination. Since the whole revolution is completed in twenty-four hours, and the hand of the clock on the face of the dial is always moved in a plane that passes through the clock's axle—making equal movements in equal time around that axle, but unequal movements around the center of the dial according to the different inclinations—and since those inclinations are the same in both the sundial and the clock-dial, it follows that the