(181) 
THE SECULAE VAEIATION OF THE MAGNETIC ELEMENTS 
IN SOUTH AFEICA DUEING THE PEEIOD 1900-1913. 
By J. 0. Beattie, D.Sc, Professor of Physics, South African College, 
Cape Town. 
(Eead May 20, 1914.) 
The study of the secular variation of the magnetic elements in South 
Africa is of more than usual interest because of the abnormal values of 
the changes. In the magnetic charts of the v^orld published by the 
British and by the United States naval authorities, the one in 1905 the 
other in 1907, the annual change off certain parts of the East African 
coast is given as 10' decrease of westerly declination, a result greater in 
absolute value than in any other region except off the east coast of South 
America. It has been possible and necessary in the course of a magnetic 
survey of South Africa to determine the secular variation not only of the 
declination but of the horizontal intensity and of the dip over the main- 
land, for approximately the same epoch as that for which the naval charts 
were issued, and thus to see to what extent the abnormal values exist on 
the mainland in South Africa. 
The period over which the observations extend is from 1898 to 1913, 
the greater number however belongs to the period 1903 to 1913 ; the 
actual results, except for the stations given at the end of this paper, have 
already been published from time to time. The method of observing and 
the reductions applied have also bepn explained in an earlier publication. 
In addition to results obtained with the same instruments in Africa south 
of the Zambesia, observations for a few other stations have been embodied 
in so far as such were available for places south of the equator. The 
extra stations thereby included are Loanda, Mozambique, Dar-es-Salam, 
Tananarive, Mauritius, and Delagoa Bay. In the first set of stations care 
was taken to make the observations at any one station at the same time 
of day, in this way obviating the necessity for the apphcation of any 
correction for daily variation, a quantity which is not known accurately 
on the South African mainland. 
