In this instance, also, since the direction lay across the sea, the distance was estimated, not measured.

Finally, as we have already related, the Khalif Al-Mamun made two sets of measures, one on the shore of the Red Sea, the other near Cufa, in Mesopotamia.

The general result of these various observations gave for the earth's diameter between seven and eight thousand miles.
This approximate determination of the size of the earth tended to depose her from her dominating position, and gave rise to very serious theological results.

In this the ancient investigations of Aristarchus of Samos, one of the Alexandrian school, 280 B.C., powerfully aided.
In his treatise on the magnitudes and distances of the sun and moon, he explains the ingenious though imperfect method to which he had resorted for the solution of that problem.

Many ages previously a speculation had been brought from India to Europe by Pythagoras.