3. The younger, so called because we have not even an adjective of place to distinguish him from Heron of Alexandria, is supposed to have lived under Heraclius (A. D. 610-641). In his own work on Geodesy (a term used in the sense of practical geometry), he says that in his own time the stars had altered their longitudes by seven degrees since the time of Ptolemy: from which the above date must have been framed. But if he spoke, as is likely enough, from Ptolemy's value of the precession of the equinoxes, without observing the stars himself, he must have been about two hundred years later. He was a Christian.