Section a.— ASTRONOMY, MATHEMATICS, PHYSICS, 

 METEOROLOGY, GEODESY, SURVEYING, ENGI- 

 NEERING, ARCHITECTURE, AND GEOGRAPHY. 



President of the Section: — Professor J. C. Beattie, D.Sc, 



F.R.S.E. 



WEDNESDAY, NOVEMBER 2. 



The President delivered the following" address : — 



EARTH MAGNETISM, WITH SPECIAL REFERENCE 

 TO SOUTH AFRICA. 



It is always a matter of difficulty for a president of a section 

 of our Association to decide on the subject of his address. In 

 the first place, each section embraces several sciences, and no 

 ■one man can deal with the whole of them ; secondly, if one 

 science be chosen the speaker runs the risk of losing^ touch with 

 his audience by taking up in detail some particular division of 

 it, or of wasting time by trying to recapitulate the advance of 

 the whole. For my own part I feel that I cannot do better 

 than choose one part of physics and limit myself to a portion 

 of that; the part is magnetism, the portion is earth magnetism 

 in South Africa. 



I shall begin by giving a short summary of what we know 

 to-day about magnets, and then give you an account of the 

 order in which the facts have come to light in history. The 

 two most striking properties of a magnet are first, its attrac- 

 tive power, and, secondly, its directive property; the latter is 

 usually specified, for that great magnet, the earth, by giving 

 the magnetic declination and the inclination. We further know 

 that these two quantities have different values at different parts 

 of the earth, and that these values change from year to year, 

 that they vary slightly with the time of day at which they are 

 observed; that they may be very seriously changed in value for 

 hours together by what we, for want of a better name, call 

 magnetic storms. I propose to shortly state when these various 

 facts were discovered, and then to tell you what we know 

 about them in this country. 



The derivation of the word magnet is of interest. Benjamin* 

 gives a full account of the various explanations which have 

 from time to time been put forward. Pliny, for example, copy- 

 ing Nicander, states that a certain stone was called the ]\Iagnes 

 Stone, because a shepherd Magnes " wdiile guarding his flock 

 on the slopes of Mount Ida, suddenly found the ferule of his 

 staff and the nails of his shoes adhering " to it. The derivation 

 of the word usually accepted is from Magnesia, in Lydia, a 

 town near which was a deposit of the natural magnetic stone 

 familiar to the ancients. The attractive power was the first 

 propertv observed; it is the foundation of many stories. I 



♦Park Benjamin : " The Intellectual Rise in Electricity." Longmans & 

 Co., London. 1895. 



