Ever since man first noticed the regular movement of the Sun and the stars, we have wondered about the passage of time. Prehistoric people first recorded the phases of the Moon some 30, years ago, and recording time has been a way by which humanity has observed the heavens and represented the progress of civilization.

Ancient Measurements of the Circumference of the Earth 1. The reconstruction of the system of ancient lineal units allows to confirm the conclusion of French scholars of the eighteenth and early nineteenth centuries that the ancients had achieved a most accurate calculation of the circumference of the earth and that this calculation had been performed earlier than Greek times.

The French scholars concluded that all the estimations reported by authors of the Hellenistic and Greek period repeat, according to different stadia, the statement of Aristotle that the mathematikoi had calculated the circumference of the earth asstadia.

Since the different stadia relate to each other by simple fractions, these scholars concluded that the ancient linear units were all modules of a single basic unit. Through medieval times there had been preserved the memory of the Roman calculation of the meridian of degree as 75 Roman miles.

Newton did not trust the accuracy of this figure and before publishing the Principia waited for the calculation of Picard, which actually proved less accurate because the toise used by Picard was slightly shorter than the toise used by other French scholars and by Picard himself in a second period.

The French scholars had not succeeded in calculating the length of the ancient Roman foot with a precision greater than 3 tenths of a millimeter. Since I have determined that the Roman foot corresponding to a libra of grams has a length of Seventy-five Roman miles indicate a degree ofm.

Contemporary data based on a geoid of regular shape and calculated at sea level indicate a degree ofm. The common practice of Roman times was to divide the Roman mile not into 10 stadia of Roman feet, but into 8 stadia of artabic feet, equal to Roman feet. Distances at sea were not calculated by Roman miles, but by artabic stadia.

The artabic foot is particularly fitted to the calculation of geographic distances, since such feet are equal to a second of degree. Hence a plethron of artabic stadia fits exactly into the sexagesimal division of the degree. The Persian parasang, equal to an hour of march, is equal to 18, artabic feet, and is divided into the triple unit called milia in Roman times; since there are 20 parasangs to a degree, there are 60 milia to a degree.

Hence, a man marching for eight hours each day in a year would make the circuit of the earth. By mathematikoi Aristotle refers either to Pythagoreans or to the followers of Chaldean mathematical science; it is not necessary to try to settle here the disputes about the meaning of the term mathematikoi in Aristotle.

By stadion the Greeks meant either the distance covered in a minute of march or the distance covered in a double minute of march; generally they called stadion the double minute of march corresponding to the division of the day into 12 double hours, but the stadion of feet or one minute of march was also used.

The stadion mentioned by Aristotle is equal to barley feet; if the feet are of the trimmed variety the circumference of the earth would be 39, m. The corresponding degree would be the one of 75 Roman miles of 20 parasangs. The French scholars gathered evidence of the use of a stadion of about m.

The Greek geographers of the Roman period report the figure ofandstadia for the circumference. Both figures are based on artabic units. The second figure is based on a stadion of artabic feet; the first on a stadion of artabic cubits. The first figure could be also calculated by a stadion of trimmed lesser feet.

Since the Greeks before the time of Aristotle did not possess the state organization necessary to proceed to the measurement of the degree, it follows that the degree had been calculated before Greek times.

If the degree had been calculated before Greek times, it follows that it was not the Greeks that discovered that the earth is a sphere. The French scholars thought that the calculation performed by Eratosthenes represents an independent figure, but this does not prove to be correct.

Eratosthenes would have calculated the distance between Alexandria and Syene as stadia, so that the circumference isstadia. At the beginning of the nineteenth century it was determined that the Egyptian royal cubit is mm.

But I have determined that the septenary cubit used in Egypt during the Hellenistic period is the Babylonian-Egyptian great cubit of The oldest known sundial is from Egypt; it dates back to around BC (19th Dynasty), and was discovered in the Valley of the Kings in Sundials have their origin in shadow clocks, which were the first devices used for measuring the parts of a day.

Ancient Egyptian obelisks, constructed about BC, are also among the earliest shadow clocks. D. Rawlins: "Methods for Measuring the Earth's Size by Determining the Curvature of the Sea" and "Racking the Stade for Eratosthenes", appendices to "The Eratosthenesâ€“Strabo Nile Map.

Is It the Earliest Surviving Instance of Spherical Cartography? The history of geodesy began in pre-scientific antiquity and blossomed during the Age of Enlightenment.

Early ideas about the figure of the Earth held the Earth to be flat (see flat Earth), and the heavens a physical dome spanning over it. Determining the earth's size By the fifth century BCE, the Greeks had firmly established that the earth was a sphere.

Although they knew it was a sphere, they didn't know how big the sphere was. Ancient Measurements of the Circumference of the Earth.

1. The reconstruction of the system of ancient lineal units allows to confirm the conclusion of French scholars of the eighteenth and early nineteenth centuries that the ancients had achieved a most accurate calculation of the circumference of the earth and that this calculation had been performed earlier than Greek times.

The Four Corners of the Earth The most common ancient theme is that of a Flat Earth surmounted by a hemispherical sky. Homeric: A flat disk surrounded by a world ocean.

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History of timekeeping devices - Wikipedia