Chap. i.), and it is of great interest as an example of the armillary sphere passing into the spherical astrolabe.
Ball, Spherical Astronomy, p. 303.
In Hydra viridis the polyp is of a green colour and produces a spherical egg with a smooth shell which is dropped into the mud.
Ptolemy Euergetes (247-222 B.C.) rendered the greatest service to geography by the protection and encouragement of Eratosthenes, whose labours gave the first ap proximate knowledge of the true size of the spherical The .