Instruments of the Restored Astronomy

EXPLANATION OF THE CONSTRUCTION AND USE.

This Quadrant, marked A B C, consists of a solid plate of OrichalcumA high-quality brass alloy, often used in the Renaissance for precision instruments because of its durability and gold-like appearance.. From the center to the circumference (A B), it measures a little more than a cubit and a half approximately 2.5 to 3 feet. Its thickness is roughly half the width of a finger. Within the circumference, it contains not only the division common to us—using transversal lines and points (which I have discussed elsewhere)—but also that NonnianA method devised by Pedro Nunes (Petrus Nonnius) to measure fractions of a degree using 45 concentric arcs; it was a precursor to the modern Vernier scale. system published by the most famous Spanish mathematician in his learned book On Twilights original: "de Crepusculis". I mentioned this system previously, though here it is expanded in a different and more convenient way so that it contains more subdivisions, especially of those numbers that can be easily divided into several whole parts. In this regard, the Nonnian invention used to present no small difficulty: for by itself, it is not sufficient for all the minutes of the entire Quadrant, much less to show the seconds of these minutes, as he [Nunes] intended. Such precision has a place in calculation rather than in practice; as often happens, beginners in this art are frequently deceived in such matters. A Table is also added, carved into the other surface of the Quadrant, which explains the Divisions and makes them very easy to use without further calculation.

The rule the alidade or sighting arm, marked D E, is made entirely of steel so that it may always remain perfectly straight. However, it is also gilded to prevent it from being corrupted by rust. It has two brass dioptraSighting vanes or plates used to align the instrument with a celestial object. around D and E. At the lower end E, it features small slits parallel to the primary sighting vane at D, where the observer’s eye is placed. This allows one to align the stars around the first sighting vane more accurately and centrally from all sides, without any optical errorBrahe uses "hallucinatione" to mean visual distortion or misalignment.. This is the method we use in almost all our instruments. The Rule itself was intentionally made longer than the radius of the Quadrant at A E; partly so that at the lower end E, it can be easily raised or lowered with the fingers during sighting until the precise altitude of the observed star is revealed, along with its AzimuthThe horizontal direction of a star, measured as an angle from a reference point on the horizon.. To ensure it remains steady wherever it is moved, a thin steel "feather" (as they call it) a leaf spring on the other side of the Quadrant near D holds and monitors it, making the observation more exact and convenient. It functions almost as if the Quadrant had a radius the length of D E; furthermore, because the lower supports do not get in the way, it is easier to handle. Let these points suffice for the explanation of the Quadrant itself.

The supports of which I speak are arranged as follows: First, the Quadrant itself rotates, attached to a certain smooth, oblong, sturdy iron rod, around H by a small screw. Thus, it can be removed whenever desired from a certain channel which has those visible rotations on the outside for the sake of stability and ornament. The channel itself carries another rule further down, represented near K and M; together with the plane of the Quadrant, it rotates conveniently toward any face of the sky above the steel Azimuthal HorizonThe base of the instrument that represents the horizontal plane, used to measure the compass direction of stars. N O P. At the same time, beneath the index K, it reveals the Azimuth of the observed star along with its Altitude in a single operation, so that the Altitudes are counted above on the Quadrant (as shown), while the Azimuths are counted on the said Azimuthal Circle. The three screws seen near the mentioned letters, as well as a fourth hidden on the other side, ensure that the steel Horizon can be positioned exactly in the plane of the true Horizon. Thus, the Quadrant resting above it is properly directed both according to the equilibrium of the Horizon and toward the ZenithThe point in the sky directly above the observer. on both its sides. There is also another screw near I which corrects the instrument in any very small differences (wherever necessary), so that it represents the plane of any vertical circle perfectly in whatever position. Furthermore, these steel screws, which carry the whole instrument, stand upon four marble columns; three of these are visible and indicated by the letters X, Y, and Z. The fourth, being identical and at the back, is not clearly seen. Finally, within these four columns is a bench or pedestal marked Q R S; this is climbed and stood upon after an observation is made so that the altitude observed on the circumference of the Quadrant can be counted conveniently and accurately. Let it suffice to have pointed out these things regarding the construction of the instrument. Any remaining small details can be easily understood by looking at the figure itself and paying diligent attention.

Its use is very broad, wherever anything involving the Altitudes and Azimuths of both the planets and the fixed stars can be adapted to astronomical observations, reduced to numbers through the science of triangles trigonometry, and serve the same. On this matter, one may consult the books of the experts, as well as those things we have commented on here and there in our own works as the subject required—especially in the second volume of my Astronomical Exercises original: "Progymnasmatum Astronomicorum", which deals extensively with the Comet of the year [15]77. Indeed, in the observations set forth there and adapted for demonstration, the primary use of this Quadrant was established, since at that time I did not have at hand the other larger instruments built in a different form. Nevertheless, this one was sufficient, as it shows individual minutes quite distinctly in both Altitudes and Azimuths. It is also explained in the said book near the end, specifically on page 461.