SECTION A.— MATHEMATICAL AND PHYSICAL SCIENCES. 



THEORIES OF TERRESTRIAL 

 MAGNETISM. 



ADDRESS BY 



DR. F. E. SMITH, C.B., C.B.E., Sec.R.S., 



PRESIDENT OF THE SECTION. 



At last year's meeting of the British Association in South Africa, the 

 following resolution was passed by Section A : 



' To urge the importance of the establishment, on a suitable site 

 in South Africa, of an observatory for the study of terrestrial 

 magnetism and atmospheric electricity. 



' The establishment of such an observatory would add very 

 greatly to the accuracy and value of the magnetic survey of South 

 Africa which is now in progress. The Committee desires to call 

 attention, moreover, to the fact that at present there is only one 

 magnetic observatory, viz. at Helwan, Egypt, and regular observations 

 in South Africa are much needed for the study of the earth's 

 magnetism.' 



This resolution, which was subsequently approved by the Council 

 of the Association, states the need for yet another observatory in the 

 Southern Hemisphere in order to advance the solution of one of the most 

 attractive problems ever presented to the physicist — the problem of 

 terrestrial magnetism. 



I would remind you, too, that last year in South Africa we had the 

 great pleasure of being welcomed by Dr. Beattie, the Principal of Cape 

 Town University, himself a great authority on terrestrial magnetism, and 

 who, in this city, at the meeting of the British Association in 1898, 

 announced that a magnetic survey of South Africa had been begun. At 

 the Bristol meeting of 1898 terrestrial magnetism played a most important 

 part. An international conference on the subject was held in affiliation 

 with Section A, and Sir Arthur Riicker, then professor of physics at the 

 Royal College of Science, who taught me most of the physics I know, was 

 president of the conference. 



When that meeting in Bristol was held I was a student of Riicker's, 

 and my first real contact with the problem of terrestrial magnetism was 

 made by experimenting with a model of Wilde's magnetarium. This was 

 a globe 18 inches in diameter, inside which was a smaller globe with wire 

 coils round it, the axis of the coils being in general inclined to the axis of 

 the outer sphere, which represented the earth. Between the two spheres 

 was a spherical shell of wire gauze supporting another coil system. With 



