294 HISTORY OF DISCOVERY RELATIVE TO MAGNETISM. 



which turns towards it shoukl be called the south pole. lu like manner the 

 end of the needle which points to the south should be called its north pole. 

 Gilbert objected to the use of this inconsistency, and introduced in its stead the 

 correct appellation, lie did not succeed, however, in abolishing the old terms, 

 altliou^-h physicists agreed with him, and even some of the more recent 

 writers un this subject have adopted his forms of expression. This is the case 

 with the French authors on magnetism, and some of the English physicists 

 have endeavored to avoid the difficulty by using the term north end for the 

 extremity of the needle which points to the north, and the south end for that 

 which is directed to the south. 



The fact was still unknown, even to Gilbert, that the deviation of the mag- 

 netic needle changes with time, and, upon the whole, there is but little trust- 

 Avorthy testimony to show to whom the discovery of the secular variation 

 of the magnetic needle is to be attributed. Although observations made at 

 Paris and London exhibit in different years a difference in the variations, the 

 idea could not be seized upon at once that the needle changed its position from 

 one year to another ; on the contrary, it appears that the differences observed 

 were considered as errors of the observations. Gellibrand, however, who observed 

 the variation in 1G34, in London, hnding it different from that observed by 

 Gunter in 1C22, and that by Burrows in 1580, concluded that the deviation was 

 variabfe, and therefore the discovery is generally ascribed to him. Although 

 the French had observed as early as 1541, 1550, 1580, and 1603, in Paris, four 

 different variations, and although Gunter, in Loudon, had also 'found a devia- 

 tion different from that of Burrows, the honor of the discovery cannot be 

 ascribed to any of them, since the one who makes a discovery is he who first 

 clearly perceives the essential particulars of the phenomena and gives an intel- 

 ligible account of them; for this reason, and, indeed, with justice, the dis- 

 covery of Uranus is ascribed to Herschel, although Flamstead had observed 

 it nearly a hundred years before, but had mistaken it for a fixed star. The 

 fact of the yearly variation of the magnetic needle was adopted and defended 

 by Gassendi, in France, and was soon generally admitted, although it was 

 thought at the time that the motion was regular, or that the north end of 

 the needle moved every year an equal amount towards the west. It was, 

 however, soon discovered that its progress was far from being regular, but it 

 was still thought that the motion was so stow that the needle might be con- 

 sidered stationary at least for a few days. But this also proved to be incor- 

 rect when Father Guy Tuchart, in 1682, observed the deviation in the city of 

 Louvo, in Siam, in presence of the King ; he found it on four, and again on 

 three successive days to assume different directions, either increasing or decreas- 

 ing. The celebrated mechanist, Graham, in London, repeated these observa- 

 tions with better instruments in 1722, and discovered that the needle changes 

 its position not only from day to day, but even from hour to hour ; that, indeed, 

 it does the same continitally, and is, in fact, in a state of perpetual motion. 

 Assessar Swedenborg, in his treatise on magnetism, expressed a doubt as to the 

 correctness of these propositions, and asserted that they were based upon errors 

 of observation. This induced the celebrated professor Celsius, at Upsala, to 

 repeat the observations of Graham. As early as in 1740 he communicated a 

 few results to the public, which showed the correctness of Graham's discovery. 



Celsius was also the first who, in company with Hiarter, observed the remark- 

 able and violent disturbances of the magnetic needle Avhich accompany the appear- 

 ance of the aurora borealis, and it was he who also first established the fact of 

 the simultaneous motion of the needle at different places on the earth. He had 

 induced Graham, in London, to make observations simultaneously with him, in 

 order to ascertain whether the disturbances of the needle depends on local 

 changes, or on those affecting large portions of the earth. After the death of 

 Celsius, Olav Hiarter continued his observations and published the records of 



