116 ~ Prof: Hansteen on the Number and Situation 
further, that the deviation is different in various places, being 
in some more westerly and others more easterly: at last, too, 
it was found that the ‘leviaticn differed at different times in the 
same places. These phenomena can only be explained by 
the assumption that the magnetic poles do not correspond 
with the geographical, and change their position from year to 
year. As there are, however, natural magnets having four 
_poles, two and two of the same denomination, the earth itself 
may possibly be such an anomalous magnet. ‘Thus, then, the 
two following questions are to be answered: Are two magnetic 
poles sufficient to explain all the phenomena of the declination, 
or must we assume several of them? What is the position and 
motion of these poles ? 
Our curiosity for obtaining a better knowledge of the mag- 
netic state of the earth must be excited from its importance to 
navigation; but it is increased by the prospect of the light that 
thereby may be thrown on natural philosophy. It is impossible 
tendere reputatur, aliquantum declinat ad occidens, illa qua ad septen- 
trionem respicere creditur, tantumdem ad oriens se inclinat. Quanta 
autem sit heec inclinatio, inveni multis experimentis versus 5 gradus.”.... 
The work is dated ‘in castris et obsidione..... (name illegible) anno Do- 
mini 1269, 8° die Augusti.”’ 
I will take this opportunity of adding another historical observation. 
Both Hansteen (Magnetism of the Earth, p. 405) ,and after him Horner 
(Gehlet’s Physical Lexicon, n. ed. vol. i. p. 137), believe, that Father Gay Ta- 
chart first discovered in the year 1682 that the advance of the needle was not 
regular, but was subject to variations. The same subject is, however, already 
mentioned in the Philosophical Transactions, vol. ili. no. 37, p. 726, in an 
Extract of a Letter written by Dr. B. to the publisher, concerning the present 
Declination of the Magnetic Needle, dated : 23rd of May 1668. The author 
of this letter says that he had received these observations from Capt. Samuel 
Sturms, an experienced seaman, who had made them in presence of the ma- 
thematician Staynred, near Bristol, on the 13th June 1666. ‘These obser- 
yations are as follows: 
- Azimuth of the F 
Height of the Sun with the |/Tv° 47"! Declination. 
Si Magn. Merid. i 
° i °o | fe} U ° 4 
44 20 72 0 70 38 1 22 W. 
39 30 80 0 78 24 1 36 
31 50 90 0 88 26 1 34 
27 42 95 0 93 36 1 24 
23 20 103 0 
101 23 1:25 
These observations were repeated by this gentleman, in the same place, 
on the 13th June 1667, and he then found that the declination was 6’ more 
west. The same seaman also said, that in different places he found a differ- 
ence in the-declination from 2’ to 7’.—Kamrz. 
for 
