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defeated by a great reef off Cape Bojador, but this was eventually passed in 1433 or 1434, and further 

 voyages became more and more directed towards trading and colonization. King John commissioned 

 an esquire of his country, Diego Cao, to continue further exploration into the Gulf of Guinea, and on 

 his second voyage in 1484-6 Diego Cao penetrated southward beyond the mouth of the river Congo 

 (Ravenstein, 1900). 



It was the custom of the Portuguese at this time to set up marble pillars surmounted by a cross, 

 with which to mark their achievements. These pillars, or 'padraos', had been introduced to replace 

 wooden crosses which were used before but found to rot away too quickly. Diego Cao carried several 

 of those padraos with him, constructed and suitably inscribed, before leaving Portugal. He set up 

 one at the most southerly point which he reached, naming it ' Cabos do Padraos '. It is now known 

 as Cape Cross. It seems that Cao sailed rather further south than this, to about 22 09' S., before he 

 returned to the north. 



Interesting to note is a remark by Ravenstein (1900) on Martellus's chart, which documented the 

 discoveries of this period. He says, ' To the south of it [Cape Cross] on Martellus' chart, we notice 

 a Praia dos Sardinhas (sardine shore), now known as Sierra Bay. . .'. The position of this shore 

 coincides with the region where we now know that extensive mortalities of fish occur. It is possible, 

 therefore, that Diego Cao had observed such a mortality of sardines. 



Diego Cao appears to have died on the return voyage, and the exploratory work was taken over by 

 Bartholomeu Diaz. Diaz left Portugal in 1487 and was the first to succeed in rounding the Cape of 

 Good Hope. He set up a padrao at Luderitz Bay (Diaz Point) and another at the Cape. The final 

 linking up of the trade route to the east was accomplished by Vasco da Gama (1497-9) (Ravenstein, 

 1898). One might conjecture that da Gama had benefited from the experience of his predecessors 

 for on his way to the Cape he stood well out to sea and first touched the South African coast at 

 St Helena Bay. In so doing he would have avoided the greater part of the contrary currents and winds 

 of this coast, and would have been able to tack into the trade wind, but there is, of course, no proof 

 that it was these considerations that led him to adopt such a route. 



Although the early Portuguese place-names are very descriptive and tell us a lot about their observa- 

 tions, no detailed records of these voyages have been found. Several expeditions visited this coast in 

 the following centuries, principally in search of guano and further inland exploration, but not until 

 the nineteenth century have we been able to find any records of meteorological and hydrographical 

 observations. 



Previous scientific observations 

 In 1820 Major James Rennell summed up the existing knowledge of the ocean currents' and this work 

 was published posthumously in 1832. With regard to the currents of the South-west African coast 

 he remarks (pp. 119 et seq.): 



But we have no detailed accounts of the circumstances of the currents along-shore, between the parallels of 28 

 and 1 ii° south, although the existence of such is well known ; so that the continuity of the thread of current is never 

 broken between that in the Indian Sea and the Equatorial current. The first notice, from authority, of a current 

 hereabout, is its issuing from the deep recess of the coast of Benguela, between 9F and n° S., in a W.N.W. and 

 N.W. by W. direction, (as if the water had been forced in there) and with a rate of 14 to 25 and 30 miles per day. 

 From the just mentioned Bay of Benguela the current ranges along the coast to the N.W. receiving the waters 

 of the Zahir or Congo River, the outfall of whose waters runs nearly in the same direction with the sea current, 

 that is N.W., and only marks its character by the increased velocity of the stream, and the lowering of its temperature. 



While commenting thus on the coastal currents, Rennell was well aware of the more definite drift 

 produced by the trade wind farther from the coast. This he called the South Atlantic current. 



