In the eccentric theory the planets move round in circles whose centres do not coincide with the Earth. Nothing here is original and Proclus is proving results first given by Hipparchus and Ptolemy . However, although Proclus believed that this theory should be studied by his students at the Academy, he was not uncritical, suggesting that the theory was overly complicated and also that it was an ad hoc theory with no reason to explain its various parts. In his astronomical writings, Proclus described how the water clock invented by Heron could be used to measure the apparent diameter of the Sun. Proclus's method can be used at the equinox .
Water is collected from the clock in a container while the sun rises.
As soon as the Sun has risen the water is collected in another container and this measurement continues until sunrise the following day. Then the ratio of the weights of water in the two containers gives the apparent diameter of the Sun. Next Main index History Topics Societies, honours, etc.