Ptolemy 

Introduction 

Claudius Ptolemy was native to Egypt. He lived and wrote at Alexandria about the middle of the 2nd century of  Christian era. He developed the principle of mathematical geography. His writings inspired geographers and explorers of the great age of discovery to explore the Terra-Incognita.

His well known works: 

• The syntaxis (Almagest), contributed to classical astronomy. Presented detailed mathematical theory of motion, of the sun, the moon and planets. He stated stars are fixed at their place and planets are much closer to earth than stars. Almagest’s two parts devoted to star catalogue, he gave the mathematical arrangement of stars. The catalogue of the Ptolemy includes 1,022 stars which are  grouped into 48 constellations.

• ‘The geography’ in 18 volumes, this book is known as Guide to geography. Accounts 26 maps of Europe, Africa and Minor Asia.

• ‘The  Tetrabiblos' deals with astrology.

• ‘The Optics’ deals with delta.

Contribution in the field of Mathematical geography: His contribution can be studied under the sub-heading of - ‘circumference of earth , Prime meridian, Graticule and Design of projection. With regard to measurement of circumference of earth he followed the view of Hipparchus and for longitude and latitude he followed Eratosthenes.

Contribution in the field of Astronomy: In the field of Astronomy, he devoted two parts of his book ‘The Almagest’. He described the mathematical arrangement of the stars and gave celestial latitude and longitude as well as magnitude for each of them. The catalogue prepared by him includes 1,022 stars grouped into 48 constellations. He also discovered the irregularities of the moon’s orbit.

Contribution to general and regional geography:

• Ptolemy describes the regions and nations of western Europe. In his second book devoted two sections to the geography of the British Isles. The maps of British Isles, constructed by Ptolemy with longitude and latitude are very closely related to the reality in shape.

• Ptolemy’s geographical enumeration of names, physical features, places, tribes and his understanding of the British Isles is of very high order.

• He gave geographical and economical descriptions of Gaul(France) and Iberia(Spain). He was more accurate about Caspian, showing it is an island sea and his knowledge of coastal regions, mountains and Islands of Caspian sea was adequately reliable.

• Ptolemy described the geography of central Asia in either side of the Imus (Altai) mountains. He gave accounts of the tribes like Abii, Alani, Issedones and many more.

Have definite information of the country to the east of scythia that is sires(china). He plotted Gangetic Gulf (Bay of Bengal) for the first time. He showed the source of Ganga and tributaries in the Himalayas. Ptolemy introduced two rivers in Africa- Gir and Niger river.

Introduction

Eratosthenes was born in Greek colony, Cyrene, in 276 B.C. He got his education at Cyrene and then at Athens. From Athens he was invited by the ruler of Egypt, and appointed chief librarian of the library of Alexandria. This post was considered to be the highest academic honor of the period. He served in the capacity for about 40 years until his death in 194B.C. During his tenure as chief librarian he wrote several scientific and literature books. All her works have unfortunately perished. He attempted  to give the subject of geography a systematic form.

Contribution in geography

• Eratosthenes may be regarded as the first scientific geographer who ascertained the length of the equator with remarkable precision. He also developed the systems of coordinates for the world that is latitude and longitude. He was well acquainted with the astronomical knowledge of the world.

• About the problems of shape, size, position and sphericity of the earth, Eratosthenes adopted the view of the Aristotle and Euclid and regarded the earth as a sphere, placed in the center of the universe, round which the celestial body revolves every 24 hours. 

• He also discovered that the sun and the moon had independent motions of their own. Thus, his idea of the shape of the earth is in conformity with the modern geographer.

• Eratosthenes also tried to measure the circumference of the earth. Apart from his contributions in Astronomy and Geography. He is famous for the correct measurement of the length of the equator with the help of an indigenous apparatus known as Gnomon. Eratosthenes, concluded that the whole world is about 25000 miles in circumference which is near to actual measurement. The only theoretical error in the measurement of the circumference of the earth was that Eratosthenes took the earth as the perfect sphere instead of an oblate spheroid. 

• Eratosthenes also attempted to determine the distance of the Sun and the moon from the earth. He computed the distance of the moon at 78000 miles and that of the sun 400000 miles. There is no account of the process by which he arrived at these conclusions. But these results are far from accurate. He also tried to determine different latitude and longitude. Eratosthenes drew a meridian southward through Alexandria, Syene, Meroe and passing through Rhode, Troade and Byzantium and the mouth of Borethenes on the north shore of black sea. In Spite of shortcoming, Eratosthenes has been called the ‘founder of Geodesy’.

• Regarding Asia he relied on the itineraries of Alexander and his record keepers. He  was also familiar with the fact that the Mt. Taurus was connected with Armenia, Kurdistan and Elburz to the Himalayas. He believed that the Ganges flowed from west to east and merged into the eastern ocean.

• Eratosthenes was well acquainted with the extent and dimension of the Red sea which he described 900 miles from the head of the Gulf to the station of Ptolemais Epitheca. His knowledge about the Nile was superior to that of his predecessors.

• The book written by Eratosthenes describes the ekumene, the inhabited earth in which he accepted both the major divisions of Europe, Asia and Libya and five climatic zones that is a torrid, two temperate and two frigged zones.

• Eratosthenes also tried to determine the spread of the world. According to his calculations, the length of known world from the Atlantic to he Eastern ocean amounted to 2800 miles, while its breadth from the parallel of cinnamon land to that of 3800 miles. He extended the habitable world from Thurles to Taprabone and from Atlantic to Bay of Bengal.