The lateen sail, as exemplified by the Arab dhow, the Bombay kotia, and so on, came into use about the 4th century B. C., but was used by Arab and Hindu, rather than Egyptian or Greek.
See Chatterton: Sailing Ships and their Story; Torr: Ancient Ships; Holmes: Ancient and Modern Ships; Pritchett: Sketches of Shipping and Craft; Lindsay: History of Merchant Shipping and Ancient Commerce; Charnock: History of Marine Architecture; Jal: Archéologie Navale.
1. Stadia.—Three stadia were in use in the Roman world at this time,—the Phileterian of 525 to the degree, the Olympic of 600, and that of Eratosthenes, of 700. Reduced to English measure this would make the Phileterian stadium equivalent to about 650 feet, the Olympic about 600 feet, and that of Eratosthenes about 520 feet. The stadium of the Periplus appears to be that of Eratosthenes. Generally speaking, ten stadia of the Periplus to the English statute mile would be a fair calculation. But it must not be forgotten that all distances named in this text are approximations, based principally on the length of time consumed in going from place to place, which naturally varied according to direction of the wind and current, of sailing-course, and other factors as well. The distance is generally given in round numbers; and without any means of arriving at an exact calculation, the figures in the text can be considered only as approximations.
According to the system of measurements laid down by Ptolemy, the circumference of the earth was estimated at 180,000 stadia, with 500 stadia to the degree.
The true length of the degree is 600 stadia.
The Olympic or standard Greek stadium (being the length of the race-course at Olympia), was 600 Greek feet, or 8 to the Roman mile. There was a later stadium of which 7½ went to the Roman mile (1000 paces, 4854 English feet). This, the Phileterian stadium, survived in Arabic science, and thence in the calculations of mediaeval Europe; being very nearly the English furlong.
According to Col. Leake's calculations,
| 1 | Olympic stadium | = | 606.75 | English feet. |
| 10 | "" | = | 6067.50 | "" |
| 1 | Nautical mile | = | 6075.50 | "" |
| 1 | Admiralty knot | = | 6086.50 | English feet. |
| or, by Clarke's measurement, Olympic stadium | 6087.11 | "" | ||
| Therefore, | ||||
| 10 | Olympic stadia | = | 1 minute of the equator. | |
| 600 | "" | = | 1 degree"" | |
