l6 PRESIDENTIAL ADDRESS. — SECTION A. 



was known in Europe before Columbus's first voyage; his 

 observations in 1492 were, however, the first to bring out be- 

 yond dispute the fact that the compass did not point in the same 

 direction at all places on the earth's surface. For long after 

 Columbus's time this knowledge was confined to seamen onlv; 

 these took it up very seriously, and it was the custom for the 

 early navigators on long voyages to determine the magnetic 

 declination at different places en route. One of the first to 

 make such determinations was de Castro.* While on a voyage 

 from Lisbon to Goa, 1538-1541, he gave the first informa- 

 tion of the declination values in the South African Seas. Near 

 St. Francis Bay he found the value 1° 30' E., in June, 1538; 

 off what is now East London, the value is given as zero for 

 th,e same year, while at the Mozambique anchorage 

 which was reached on August loth, 153S, the value was 

 6° 45' W. I may also mention Corn. Houtmann, another of 

 the early seamen who made observations in South African 

 waters. He determined the declination in or near IMossel Bay 

 on August 4th, 1595. and found it to be zero. 



Not only has the magnet a declination ; it has also an inclina- 

 tion. The discovery of this is first mentioned in 1544 by Georg 

 Hartmann in a letter to Prince Albrecht of Prussia. The con- 

 tents of this letter were not published, and the inclination was 

 again discovered by Robert Norman, who made his knowledge 

 known in a little work called " The Newe Attractive," pub- 

 lished in 1581, the first work on terrestrial magnetism. He 

 determined the dip in London, in the year 1576, to be 71° 50' 

 N. The next determination of the dip was also made in 

 London in 1600, and by Gilbert, a man whose name must 

 always receive honourable mention in any account of the 

 development of magnetical discoveries and theories.! His 

 book, " De Magnete," was published in 1600, and contains a 

 most complete summary of the properties of magnetic bodies, 

 as they were known at that date. Gilbert's own contribution 

 is the suggestion that the earth is itself a great magnet. The 

 heading of chapter 17 of Book L is 



" That the globe of the earth is magnetick and a magnet ; and how in our 

 hands the magnet stone has all the primary forces of the earth, while the 

 earth by the same powers remains constant in a fixed direction in the 

 universe." 



He illustrated his argument by reference to a spherical steel 

 magnet called a terrella. with this and a small magnet he shows 

 how the direction of the earth's field must vary from place to 

 place. His views on declination and inclination he illustrated 

 by the same means. He believed — what we now know not to 

 be the case — that the earth's magnetic poles coincided with the 

 geographical ones; he was not aware, however, that the vari- 



* Van Bemmelen : "Die Abweichung der Magnetnadel" : Observation. 

 of the Royal Magnetical and Meteorological Observatory at Batavia. Vosl 

 XXI. Supplement. 



' t William Gilbert of Colchester, physician of London. On the magnet, 

 magnetick bodies also, and on the great magnet the earth ; a new physiology, 

 demonstrated by many arguments and experiments. Chiswick Press, I-ondon. 

 1900. 



