1813, 41 91 35' 23 40 92 18 22 9 93 22 23 47 92 21 Mean, 22' 50' Mean, 92 24' By placing this result beside former determina tions, we have, Distance of N. Lon. West of from Pole. Greenwich.
1730, 19° 15' 6' 1769, 19 43 100 2 1613, 22 50 92 24 Hence we have, :\ lotion of the Pole N. Annual to the East. Motion.
From 1730 to 1769, - 17.44 From 1769 to 1813, - 10 .41 Mean motion, - - 11%425 Period of complete revolution, 1890 years.
These results have received a very remarkable confirmation from the observations both of the va riations and dip made during the voyages of Capt. Ross and Capt. Parry. In August 1819, Capt. Par ry was north of the magnetic pole, and from his measure of the dip, viz. 88° 37', on the I Ith Sep tember 1819,the expedition must have been about 3° north of the magnetic pole; but they were then in 74° 27', consequently the pole must have been in 71° 27', or its distance from the pole of the globe must have been 18° 33'. We may therefore conclude, that the position of the strongest pole N in the northern hemisphere is well determined.
2. On the Position of S. the strongest Magnetic Pole in the Southern hemisphere, south of New Holland.
By combining the observations made by Captain Cook in 1773 and 1777, and those made by Four neaux in 1773, Professor liansteen has obtained the following results, from which two of the most dis cordant are rejected: Distance of the l'nle S from 1,m. East of the Pole of the Earth. Greenwich.
20° 26' 138' 7' 20 6S 135 12 21 30 132 47 19 47 136 31 19 53 136 25 20 27 EIS 29 19 39 13S 11 21 4S 134 21Mean, 20' 33'.5 Mean, 136' 15.4 But, in the year1642,Prof. Hansteen found these po sitions, from the observations ofJansenTasinan,to be, Distance horn Pole, IS° 55' Lon. East of Greenwich, 146 59 Hence, in 131 years, the pole S has moved west ward 10° 14' or 4'.69 per annum.
Its period of complete revolution will be 4605 years.
3. On the Position of it, the weakest Magnetic Pole in the North Hemisphere in Siberia.
By combining a number of observations made in 1805 at Tobolsk, Tara, and Udinsk in Siberia, Pro fessor Hansteen obtained the following results: Distance of 71 from Lon. East from the Pole of the Earth. Greenwich.
4' 27' 116' 27' 4 50 115 51Mean, 4 38' 30" Mean, 116 19' But, in 1770, Professor Hansteen found the] posi tions of this pole to be, Distance from Pole in 1770, - -1' 14' Lon. East from Greenwich, 91 29 30" Hence in 35 years, the pole n has moved 35' 30% or 35.'128 per annum.
Hence it appears, that the magnetic pole 71 has a motion front west to east, and that its period of complete revolution is 860 years.
4. On the position of s, the weakest Magnetic Pole in the Southern hemisphere south of Terra del Fuego.
By combining the observations made by Captain Cook and Fourneaux in 177.1, Professor Hansteen has obtained the following results: Distance of the Pole s from Lon. West from the Pule of the Earth.- Greenwich.
12' 36' 122' 5Y 12 44 122 21 13 15 120 42 12 46 7 12 47 123 48Mean, 12° 431' Mean, 17' But, in 1676, from observations mentioned by Halley in the Phil. Trans. No. 48, Professor Han steen found the position of this pole to be, Distance from the Pole in 1670, 15° 53' Lon. West from Greenwich, . 94 33,.
Hence, in 104 years, the pole s has moved west ward 28° 4SV or 1 6'.5 7 annually; and we have its period of complete revolution, 1303 years.
From these determinations, it appears that the two magnetic poles in the northern hemisphere, Nand n, move eastward, while the two S, s, in the southern hemisphere move westward.
As the poles N and S are nearly about the same distance from the terrestrial poles, and, therefore, almost diametrically opposite, and as they are also much stronger than n and s, Professor Hansteen properly assumes, that X and S arc the terminating points of one magnetic axis, and n and s those of the other axis. Therefore, says he, these two magne tic axes cross without intersecting one another, or passing through the centre of the earth. The cen tre of both lie much nearer the surface in the South Sea than in our hemisphere.
In answer to the question which naturally arises respecting the cause of these remarkable phenome na, Professor Hansteen makes the following obser vation: It is possible that the illumination and heating of the earth, during one revolution about its axis, may produce a magnetic tension, as well as it produces the electrical phenomena, and that the change of position in the magnetic axis may be explained from a change of position in the earth's axis to its orbit.
Professor Hansteen next proceeds to show how the changes in the variation and dip of the needle may be explained by the motion of the magnetic poles; and he begins with the observations made at Paris, where the variation was as follows: Declination of Declination of Years. the Needle. the Needle.