On the ceiling of the Memnonium at Thebes the heliacal rising of Sirius is represented under the form and name of Isis. The coincidence of this rising with the annual rising of the Nile is mentioned by Tibullus and Aclian. About 4000 B.C. the heliacal rising of Sirius coincided with the summer solstice (about June 21) and the beginning of the rising of the Nile. The festival in honour of this event was held by the Egyptians about July 20, and this marked the beginning of the sacred Egyptian year. On the summit of Mount Pelion in Thessaly there was a temple dedicated to Zeus, where sacrifices were offered at the rising of Sirius by men of rank who were chosen for the purpose by the priests and wore fresh sheepskins. Sirius seems to have been worshipped by the ancient Egyptians under the name of Sothis, and it was regarded as the star of Isis and Osiris. The last name without the initial O very much resembles our modern name. According to Al-Sufi, the Arabians called Sirius _al-schira al-abûr_, "Sirius which has passed across," also _al-schira al Jamânija_, "the Sirius of Yémen." He says it is called _al-abûr_, "because it has passed across the Milky Way into the southern region." He relates a mythological story why Sirius "fled towards the south" and passed across the Milky Way towards Suhail (Canopus). The same story is told by Albufaragius[439] (thirteenth century). (The story was probably derived from Al-Sufi.) Now, it seems to me a curious and interesting fact that the large proper motion of Sirius would have carried it across the Milky Way from the eastern to the western border in a period of 60,000 years. Possibly the Arabian story may be based on a tradition of Sirius having been seen on the opposite, or eastern, side of the Milky Way by the men of the early Stone Age. However this may be, we know from the amount and direction of the star's proper motion that it must have passed across the Milky Way from east to west within the period above stated. The Arabic name _al-abûr_ is not, therefore, a merely fanciful one, but denotes an _actual fact_. The proper motion of Sirius could not possibly have been known to the ancients, as it was only revealed by accurate modern observations.