24 PRESIDENTIAL ADDRESS. SECTION A. 



evolve. The similarity between the two does not end there; 

 fraud is practised with one as much as with the other, and in 

 the case of the iron ore prospector it is not unusual to find that 

 the behaviour of the magnet is different according as the user 

 is a buyer or a seller. 



When we come to consider South African magnetic surveys, 

 the first thing that strikes our attention is the late period at 

 which such surveys have been begun. We have already 

 seen from Rennell's note what was known at the end of the 

 eighteenth century. In a summary of available mag- 

 netic data for the various continents given in the in- 

 troduction to Berghaus's "Atlas des Erdmagnetismus," * we 

 find, as late as 1891, Neumayer pointing out that over the 

 whole of this vast continent observations had been made at 

 only a few places on the coast; that the magnetic state of the 

 interior was quite unknown, and that so long as such a state 

 of affairs continued it was impossible to undertake a thorough 

 study of the earth's magnetic state. At that time the only 

 magnetic results for places in the interior of Africa were those 

 due to Capello and Ivens. These two travellers started from 

 Loanda, in Portuguese West Africa, in September, 1877, and 

 after spending a little over two years, chiefly in Angola, re- 

 turned to Loanda in October, 1879. In the accountj of their 

 journey, published in Lisbon in 1881, magnetic chartsj are 

 given which show the declination, the dip, and the total inten- 

 sity. The epoch is 1879, and the charts include the regions 

 between 6° and 16° South latitude, and between 12° and 20° 

 East longitude. The lines are quite flat and regular. How 

 they were obtained I have not been able to find out. The 

 same two travellers made a second journey in Africa during 

 1884 and 1885. -^^ account^ of this was published in Lisbon 

 in 1886, and it contains the results of observations at 23 

 stations, extending from Mossamedes on the west, through 

 Angola and North-Western Rhodesia to Tete on the Zambesi. 



The first extended survey in Africa south of the equator was 

 carried out in the Congo territories. The observers were 

 Delport and Gillis, |! who w-orked together in 1890 along the 

 lower reaches of the Congo and Lemaire,1[ w'ho made two jour- 

 neys, one from 1898 to 1000 in the Katanga district and along 

 the west shores of Lake Tanganyika. On this journey he 

 observed at 120 stations ; in his other journey** Lemaire went 

 from the Congo to the Nile in 1902 to 1904, when he occupied 

 another 35 stations. Unfortunately, in all these Congo expe- 



* Atlas des Erdmagnetismus, S. 4, Berghaus Physikalisches Altas, Abt. IV. 

 Gotha, 1 891. 



t De Benguella as Terras de lacca. Capello and Ivens, Lisbon, 1881. 



J Hellmann, Loc. cit. 



§ De Angola a contra Costa. Capello and Ivens, Lisbon, 1886. 



11 Observations Astronomiques et Magnetiques executees sur le territoire 

 del'Etat Independant du Congo, MemoiresCouronnesTome LIII. L'Academie 

 Royal des Sciences, Brussels, 1893- 1894. 



% Mission Scientique du Katanga. Lemaire, Publications de I'Etat Indepen- 

 dant dii Congo, Brussels, 1901. 



** Mission Scientifique du Congo-Nil. Lemaire, Public, de I'Etat Indepen- 

 dant du Congo, Brussels, 1905. 



