years. Every dhow-owner in Oman and the Persian gulf (not to mention the coastal craft of India) thoroughly understood the business, and all of them arranged voyages accordingly. But this information they kept to themselves. The real discovery made by this Greek was not one of geography at all but one of meteorology. He grasped the fact that Indian ocean weather differed from Mediterranean and even Red sea conditions; for during certain months it was possible to count on monsoon winds with great certainty. Now in the Mediterranean there was "sailing weather", mostly calm, and weather when it was impossible to sail. Prevailing winds in the latter period were inclined to be boisterous, the sea very rough, so the ships hauled out -- the whole procedure is described in Homer, in Pindar's Odes, and other writings. A wandering Greek heard, whilst on a voyage, that in the Indian ocean there were periods when sailing was unsafe, but for a period of six to eight months it was quiet; the wind during part of the quiet months was mainly north-eastern to northerly in direction, and storms and cyclones were not met with; only an occasional squall of short duration might be encountered. Now, where did he get this information? -- for Hippalus could not have been sufficiently long in the Indian ocean to have observed it for himself. There can, I think, be little doubt that some sailor from an Arab dhow, who had been accustomed to sail for many voyages