<Li> Eratosthenes also calculated the Sun's diameter . According to Macrobious, Eratosthenes made the diameter of the Sun to be about 27 times that of the Earth . The actual figure is approximately 109 times . </Li> <Li> During his time at the Library of Alexandria, Eratosthenes devised a calendar using his predictions about the ecliptic of the Earth . He calculated that there are 365 days in a year and that every fourth year there would be 366 days . </Li> <Li> He was also very proud of his solution for Doubling the Cube . His motivation was that he wanted to produce catapults . Eratosthenes constructed a mechanical line drawing device to calculate the cube, called the mesolabio . He dedicated his solution to King Ptolemy, presenting a model in bronze with it a letter and an epigram . Archimedes was Eratosthenes' friend and he, too, worked on the war instrument with mathematics . Archimedes dedicated his book The Method to Eratosthenes, knowing his love for learning and mathematics . </Li> <P> Eratosthenes proposed a simple algorithm for finding prime numbers . This algorithm is known in mathematics as the Sieve of Eratosthenes . </P>

Who measured the circumference of the earth for the first time