R.R. Newton WAS PERFECTLY RIGHT:
It is well known that all longitudes in Ptolemy’s Geography are cumulatively overestimated, so that his map is excessively stretched from west to east as compared with the modern map. In recent years, a number of scholars have suggested that this stretching can be explained as a result of the change in the value of the Earth’s circumference from a larger one proposed by Eratosthenes to a lesser one by Posidonius. As a result, all distances converted from linear units to angular became overestimated. This explanation has a necessary presupposition that the error in longitude on Ptolemy’s map grows linearly. This article argues that the error in longitude on Ptolemy’s map varies considerably depending on longitude, latitude and region. In particular, it grows most slowly in the Eastern Mediterranean, which is probably due to the fact that this region was the center of the ancient world. Therefore, the error in longitude on Ptolemy’s map cannot be explained by one universal reason, but only by a combination of different factors.
Dmitry Shcheglov
https://www.researchgate.net/publicatio ... _Revisited
https://cyberleninka.ru/article/n/oshib ... -ptolemeya
History of longitude
Finding an accurate and practical method of determining longitude took centuries of study and invention by some of the greatest scientists and engineers. Determining longitude relative to the meridian through some fixed location requires that observations be tied to a time scale that is the same at both locations, so the longitude problem reduces to finding a way to coordinate clocks at distant places (Sic!). Early approaches used astronomical events that could be predicted with great accuracy, such as eclipses, and building clocks, known as chronometers, that could keep time with sufficient accuracy while being transported great distances by ship. Later methods used the telegraph and then radio to synchronize clocks. Today the problem of longitude has been solved to centimeter accuracy through satellite navigation.
Ptolemy, in the 2nd century CE, based his mapping system on estimated distances and directions reported by travellers.
No maps (or manuscripts of his work) exist that are older than the 13th century, but in his Geography he gave detailed instructions and latitude and longitude coordinates for hundreds of locations that are sufficient to re-create the maps.
Apart from the difficulties in estimating rectilinear distances and directions, the most important of these is a systematic over-estimation of differences in longitude. Thus from Ptolemy's tables, the difference in Longitude between Gibraltar and Sidon is 59° 40' 0', compared to the modern value of 40° 23'0', about 48% too high. Russo (2013) has analysed these discrepancies, and concludes that much of the error arises from Ptolemy's underestimate of the size of the Earth, compared with the more accurate estimate of Eratosthenes – the equivalent of 500 stadia to the degree rather than 700. Given the difficulties of astronomical measures of longitude in classical times, most if not all of Ptolemy's values would have been obtained from distance measures and converted to longitude using the 500 value.
Islamic scholars knew the work of Ptolemy from at least the 9th century CE, when the first translation of his Geography into Arabic was made. He was held in high regard, although his errors were known.[10] One of their developments was to add more locations to Ptolemy's geographical tables with latitudes and longitudes, and in some cases improving the accuracy.[11] The methods used to determine most of the longitudes are not given, but a few accounts do give details.
Mercier (1992) notes that this is a substantial improvement over Ptolemy, and that a comparable further improvement in accuracy would not occur until the 17th century in Europe.
Mercier, Raymond P. (1992). "Geodesy" (PDF). In Harley, J.B.; Woodward, David (eds.). The History of Cartography Vol. 2 Cartography in the Traditional Islamic and South Asian Societies. University of Chicago Press.
At the end of the medieval period, Ptolemy's work became directly available with the translations made in Florence at the end of the 14th and beginning of the 15th century.
Gautier Dalché, P. (2007). "The reception of Ptolemy's Geography (end of the fourteenth to beginning of the sixteenth century)". In Woodward, D. (ed.). The History of Cartography, Volume 3. Cartography in the European Renaissance, Part 1 (PDF). Chicago: University of Chicago Press. pp. 285–364.
Telescopes and clocks
In 1608 a patent was submitted to the government in the Netherlands for a refracting telescope. The idea was picked up by, among others, Galileo who made his first telescope the following year,
The second important technical development for longitude determination was the pendulum clock, patented by Christiaan Huygens in 1657.[30] This gave an increase in accuracy of about 30-fold over previous mechanical clocks – the best pendulum clocks were accurate to about 10 seconds per day.[31] From the start, Huygens intended his clocks to be used for determination of longitude at sea.
Huygens, Christiaan (1669). "Instructions concerning the use of pendulum-watches for finding the longitude at sea". Philosophical Transactions. 4 (47): 937–953. Bibcode:1669RSPT....4..937.
Huygens was also the first to use a balance spring as oscillator in a working clock, and this allowed accurate portable timepieces to be made. But it was not until the work of John Harrison that such clocks became accurate enough to be used as marine chronometers.[
