which extended to its mouth, he established governors from the isthmus of Suez, along the Arabian and African coasts, as far as the straits of Babelmandeb; and planted colonies of Greeks and Egyptians to carry on the commerce, and protect the interests of his subjects.  But the most extraordinary instance of his enterprising spirit is to be found in his conquest (evidently for the purpose of facilitating and securing the commerce of the Red Sea) of part of Abyssinia.  The proof of this, indeed, rests entirely on an inscription found at Aduli, which there can be no doubt is the harbour and bay of Masuah; the only proper entrance, according to Bruce, into Abyssinia.  The inscription to which we have alluded was extant in the time of Cosmas (A.D. 545), by whom it was seen.  From it, Ptolemy appears to have passed to the Tacazze, which he calls the Nile, and to have penetrated into Gojam, in which province the fountains of the Nile are found.  He made roads, opened a communication between this country and Egypt, and during this expedition obliged the Arabians to pay tribute, and to maintain the roads free from robbers and the sea from pirates; subduing the whole coast from [Leucke->Leuke] Come to Sabea.  The inscription adds:  “In the accomplishment of this business I had no example to follow, either of the ancient kings of Egypt, or of my own family; but was the first to conceive the design, and to carry it into execution.  Thus, having reduced the whole world to peace under my own authority, I came down to Aduli, and sacrificed to Jupiter, to Mars, and to Neptune, imploring his protection for all who navigate these seas.”

Ptolemy Euergetes was particularly attentive to the interests of the library at Alexandria.  The first librarian appointed by Ptolemy the successor of Alexander, was Zenodotus; on his death, Ptolemy Euergetes invited from Athens Eratosthenes, a citizen of Cyrene, and entrusted to him the care of the library:  it has been supposed that he was the second of that name, or of an inferior rank in learning and science, because he is sometimes called Beta; but by this appellation nothing else was meant, but that he was the second librarian of the royal library at Alexandria.  He died at the age of 81, A.C. 194.  He has been called a second Plato, the cosmographer and the geometer of the world:  he is rather an astronomer and mathematician than a geographer, though geography is indebted to him for some improvements in its details, and more especially for helping to raise it to the accuracy and dignity of a science.  By means of instruments, which Ptolemy erected in the museum at Alexandria, he ascertained the obliquity of the ecliptic to be 23 deg. 51’ 20”.  He is, however, principally celebrated as the first astronomer who measured a degree of a great circle, and thus approximated towards the real diameter of the earth.

The importance of this discovery will justify us in entering on some details respecting the means which this philosopher employed, and the result which he obtained.