82 SCIENCE IN AFRICA 



Lufira River have been harnessed and develop 45,000 h.p. In 

 the large mining areas in the southern part of Africa the proximity 

 of coal-fields makes water-power unnecessary. In Uganda, a 

 scheme is being considered for using the Ripon and Owen Falls 

 to supply electricity to Jinja, Kampala, Entebbe and possibly the 

 Kakamega Goldfields. 



GEOPHYSICAL PROSPECTING 



Geophysical prospecting has been developed only in recent 

 years and its value is still a matter of controversy. Much more 

 fundamental research is certainly required in order to determine 

 the physical and geological conditions under which indications on 

 the instruments are obtained, and particularly where electrical 

 methods are used, the relation of rock conductivities to the amount 

 and kind of the fluid content of the various kinds of rocks; neverthe- 

 less it may be claimed that fundamental research has reached a stage 

 which warrants a thorough examination of its possibilities in Africa, 

 especially for the location of underground water in arid regions. 



Interest in geophysical work has been widely aroused as a result 

 of extensive testing of methods in Australia in 1928-30, under the 

 joint auspices of the Australian Government and the Empire 

 Marketing Board. Mr. A. Broughton Edge, one of the best- known 

 exponents, was in charge of the investigations, and the report 

 (1932) is an illuminating document. 



Methods of geophysical prospecting (Broughton Edge 1932), 

 which of course are not all suitable for the same purpose, are 

 divided into i. Magnetic, 2. Gravimetric, 3. Electrical: (a) Surface 

 potential, and (b) Electro-magnetic, and 4. Seismic. The gravi- 

 metric method requires very expensive apparatus (torsion balances) 

 and a high degree of skill. The seismic method, which depends on 

 making explosions at the surface and measuring the time for the 

 percussion to be reflected off subterranean bodies and recorded 

 by seismometers at various distances, is also expensive. The mag- 

 netic and electrical methods are much cheaper and are generally 

 of wider application. They are discussed in some detail in relation 

 to the finding of ground water, with the aid of numerous diagrams, 

 by Bruckshaw and Dixey (1934). 



