have the same relative position. From a comparison of the observations made at different times, he found that these poles had a constant motion.

The motion of both the northern poles is from W. to E. obliquely, and of both the southern ones also obliquely from E. to W. With regard to the velocity of their motion, Prof. Hansteen acknowledges that the observations are not sufficiently numerous, but he has obtained the following results: N is the strongest pole in the north hemisphere, and its revolution round the north pole of the earth is performed in 1740 years.

S is the strongest pole in the south hemisphere, and its revolution round the south pole of the earth is performed in 4609 years.

n is the weakest pole in the north hemisphere, and its revolution is performed in 860 years. s is the weakest pole in the south hemisphere, and its revolution is performed in 1304 years. POLE N, POLE S, Strongest Pole in Strongest Pole in

POLE N, POLE 8, Weakest Pole in Weakest Pole in North Hemisphere. South Hemisphere North Hemisphere. South Hemisphere.

These results have received a very remarkable confirmation from the observations both of the variations and dip made during the voyages of Capt. Ross and Capt. Parry. In August 1819, Capt. Parry was north of the magnetic pole, and from his measure of the dip, viz. 88° 37', on the 11th September 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 Hansteen has obtained the following results, from which two of the most discordant are rejected:

Distance of the Pole S from the Pole of the Earth.

Lon. East of Greenwich. 138' 7'

8'

4° 35′ 131°

43′ 12°

10' 130° 28′

4

42 135

54 11

35

4

48 140

6 11

47

4

54 144

1

5

0148

1800, 20° 7' 93° 33' 20° 53′ 134° 1810, 20 15 91 28 21 1 133 21 57 133 14 8 132 44 135 59 1820, 20 22 89 24 21 1830, 20 30 87 19 21 16 131 17 11 31 137 45 1840, 20 38 85 15 21 23 131 28 11 19 140 31 1850, 20 46 183 10 21 31 130 14 5 0152 40 11 6 143 16 Since this table was computed, Professor Hansteen has obtained many new sets of magnetical observations, and particularly those which have been made during the British Voyages of discovery to the Arctic Regions. These he has diligently compared, and he has thus obtained new determinations of the position and times of revolution of the magnetic poles of the earth. The results of these we shall now lay before our readers in a very abbre viated, but, we trust, intelligible and useful form. 1. On the Position, &c. of N. the strongest Magnetic Pole in North America.

By combining four observations on the declination of the needle, made on board his Majesty's sloop Brazen in Hudson's Bay, in 1813, and which Prof. Hansteen inspected in the Marine Chart office at the Admiralty in London, he obtained the following results:

135 12

132 47

136 31

136 25

138 29

138 11

134 21

Mean, 136 15.4

But, in 1676, from observations mentioned by Halley in the Phil. Trans. No. 48, Professor Hansteen found the position of this pole to be,

Distance from the Pole in 1670, 15° 53' 94 331 Lon. West from Greenwich, Hence, in 104 years, the pole s has moved westward 28° 43' or 16'.57 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, N and 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 N and S are the terminating points of one magnetic axis, and n and s those of the other axis. Therefore, says he, these two magnetic axes cross without intersecting one another, or passing through the centre of the earth. The centre 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 phenomena, Professor Hansteen makes the following observation: 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:

Now it appears that, in 1580, the Siberian pole n was about 40° east of Greenwich, or to the north of the White Sea, while the North American pole N was about 136° west of Greenwich, or about 30° east of Behring's Straits. The pole n, therefore, lay nearer Europe than now, and the pole N was more remote. Hence the former exercised a predominant action, and the needle turned towards the east. In the mean time, the pole n withdrew itself towards the Siberian Ocean, and as N approached Europe, its action increased, and the needle turned westward till 1814, when it reached its greatest declination, and since that time it is evidently return ing eastward. On the very same principles we see the reason why the eastern declination was less before 1580.

The variations of the needle in the Southern hemisphere are explicable in the same way. At the Cape of Good Hope, and in different bays of the adjoining

Now, in 1605, the South American pole s was 76° west of Greenwich, nearly south of Terra del Fuego, and the New Holland pole S was about 150° east of Greenwich; the poles was, consequently, much nearer the Cape than it is now, while the other pole S was more remote from it. The effect of s, therefore, was greater, and of S less than at present, so that the south pole of the needle moved more towards the west, and its north pole more towards the east. But as s went farther off, and S approached the Cape, the south pole of the needle turned more and more towards S, so that the declination became westerly.

To obtain an example from the dip, Professor Hansteen gives the following observations at Paris:

Years. 1671

1754

1780

Dip. 71° 0

72 15

71 40

Years.

1798

1814

1829

Dip. 69° 26'

68 32

67 41

Though the dip thus diminished at Paris, yet it increased in Eastern Siberia and Kamtschatka. Both these changes are the results of the motion of the Siberian pole n towards the east, in which it is removed from Europe, and approaches to Kamtschatka. In all S. America the dip decreases in consequence of the motion of the Terra del Fuego pole s towards the west.

care.

In order to discover the nature of the forces by which the phenomena of terrestial magnetism are produced, Professor Hansteen resolved to determine the intensity of magnetism in different parts of the earth's surface, and then to ascertain the form of the isodynamical magnetical lines, or those of equal intensity. He accordingly had a magnetic needle of a cylindrical form constructed with great This needle he entrusted to various philosophers, who counted the time in which three hundred horizontal oscillations were performed, in various parts of Norway, Sweden, Denmark, Prussia, Holland, France, England, and Scotland. The greater number of these were made by Professor Hansteen himself, many of them by M. Naumann, several by M. Erichsen, and a considerable number by Professor Oersted of Copenhagen, when he was travelling in England in 1823. Those which were made by this last philosopher in Edinburgh on the 4th of July, 1823, and at which we had the pleasure of assisting, were performed in the field behind Coates Crescent, and nearly at the intersection of Walker Street and Melville Street. These possess considerable interest, as being the most westerly of all that were then made.

In order to determine the intensity of the magnetic force throughout Scotland, Dr. Brewster ordered, for the Royal Society of Edinburgh, one of the instruments used by Professor Hansteen. When this instrument arrived from Christiania, where it was executed under Professor Hansteen's

These various results have been laid down on a map by Professor Hansteen; but as they occupy only a small part of Europe, we do not think it necessary to copy his chart. Any of our readers, however, may easily lay down, upon a map of Europe, the lines of equal magnetic intensity, either from the above tables, or more simply by the following directions:

1. The line of 750, or the line in which the 750 seconds are required for the performance of 300 oscillations, passes one-fourth of a degree to the south of Paris and Rheims, and one third of a degree to the south of Gotha and Gaslin.*

2. The line of 775 passes about one-third of a degree south of London, and through Amsterdam and Lubeck.

3. The line of 800 passes about the fifth of a degree north of York, Sporring in Jutland, and Falkenberg in Sweden.

4. The line of 820 passes through Edinburgh, and a little to the south of Christiansand in Norway, and Carlstadt in Sweden.

5. The line of 865 passes through Hirdal in Norway.

As the lines are almost equi-distant, and nearly parallel, all the intermediate ones may be readily inserted.

Professor Hansteen has added the following very interesting table, containing the observed dip of the needle, and the computed magnetic intensity in various parts of the world, that of the equator be ing_unity or 1.0000. A similar table was printed in Professor Hansteen's paper, in Poggendorff's Annalen der Physik, but the column of intensity had been wrong computed for all the places in the north of Europe, and we are happy to be able, through Professor Hansteen's kindness, to present our readers with a corrected copy.

South.

75° 50′1.5773 |Nimes

70 48 1.6133 Mailand

25 40 0.9348 Montpellier

20 37 0.9532 Airola

9 59 1.0773 Turin

0 0 1.0000 Medina del Campo North.

3 11 1.0191 Como

65 53 1.3482 Korset

72 24 1.3735

65 55 1.3090 Quistrum

72 27 1.4070

66 166

3 1.3364 Skieberg

72 29 1-3725

91.2938 Elleoen

72 38 1.3340

91.3227 Helgerone

72 39 1.3980

66 12 1,3104 Soner

72 41 11.3835

66 12 1.3488 Christiania

72 34 1.4195

72 45 1.4208

66 22 1.3138

Bogstad

72 34 1.4378

66 22 1.3441 66 42 1.3069 66 53

Bogstadberg Nasoden

73 13 1.4195 73 21.4517

1.3228 Bärum

Bolkesjoe

72 44 1-3902 73 15 1-4053

67 30

1.3155 Ingolfsland

73 19 1.4159

67 40 1.3155 Norsteboe 67 41 1.2938 Drammen 41.3569 Maursäter

73 33 1.4136

73 371-3771

73 44 1.4656

Ullensvang

73 441-4260

42 10 1.3155 Ferrol

Paris

68 32 1.2617 Kongsberg 69 12 1.3482 Tomlevold 69 29 1,3485 Bekkervig 53 1.3703 Vang 69

73 45 1.4221 73 47 1.4144] 73 50 1.4246 73 58 1.4114) 73 59 1.4308

31.4220

68 21 1.3509 Bergen

74

68 50 1.3533 Moe

69 44 1.3737 Mauristuen

69 57 1.3697 Leierdal

70 13 1.3742 Slidre

74 34 1.4543

70 36 1.3814 Brassa

70 36 1.3672 Davis Straits,

74 21 1.4471

70 50 1.3650 68° 22' n. 36° 10/ w. 83

70 52 1.3782 70 53 1.3846 70 57 1.3842 70 59 1 4028 71 13 1.3838 71 271.3660 71 39 1.3666 71 48 1.3842||

Hare island,

81.6365

70° 26' n. 37° 12′ w. 82 49 1.6406

Baffin's Bay,

75° 5' n. 42° 43' w. 84

75 51-45 26

251.6169

84

444 1.6410

This valuable table of results received many additions from the experiments by Captain Sabine, in the two arctic voyages of discovery performed in 1818, 1819, and 1820, and in a voyage performed in 1822, to the equatorial shores of the Atlantic, and to some of the islands of that and the Caribbean sea, and lastly, in a fourth voyage, made in 1823, to Greenland, Spitzbergen, and Norway. But not withstanding these valuable accessions, professor Hansteen was desirous of performing a journey into Siberia, for the purpose of establishing, by actual observation, the existence of a weaker pole in the north of Asia, and of extending the isodynamical lines of Europe as far as possible to the east. From this journey he has just returned, after the successful execution of his most sanguine wishes. We wait with anxiety for the publication of his observations; but we are enabled in the mean time to present our readers with a small chart of the northern hemisphere, as drawn by Captain Sabine from the observations communicated to him by professor Hansteen, combined with his own and with those given in the preceding table.

In this map, the full-drawn black lines pass through the stations where the magnetic intensity was observed to be equal, and the dotted parts of the same lines indicate the presumed direction of the curve in those regions where observations have not yet been made. The portions round the American pole are drawn principally from Captain Sabine's observations, and the prolongation of the same portions of the curves round the Asiatic pole are drawn from the recent observations of Hansteen. The American pole is situated nearly in 60° of North Lat. and 80° of Lon. West of Greenwich. The Asiatic pole is situated in 102° of East Lon., (180° distant from the American one) and in 60° of North Lat.

The first, or most northern curve, is that in which a needle which performed a given number of oscillations in 300 seconds in London, performed only 269 at all places under the curve. Round the Asiatic pole this curve will be seen to contain a smaller space than round the American pole, which proves the inferior activity of that pole. M. Hansteen traced the south part of this curve below 60° of latitude from the river Jenisei to the west, as far as the 115th degree of Lon.; that is, 25° beyond the Jenisei, and to the Lat. of 60°, where it takes a direction almost from S. to N.

The next curve, or that in which the same needle performs the same number of oscillations in 278. seconds. This curve goes round both the American and the Asiatic poles, including both within its arc. It passes to the N.W. of Melville Island, and to the N.E. of some stations on the west coast of Greenland, and it cuts the American coast between the Havana and New York. The same curve has been traced in Asia, by Dr. Erman, who accompanied Hansteen from the embouchure of the Oby, in Lat. 68°, and E. Lon. 70°, following the direction of the river Mina as far as Lat. 60° N. Here the curve gradually bends to the east, passes between Tobolsk and Narym, and was found again by M. Hansteen at Kainsk, a few degrees to the south of Lake Baikal.

The third curve, or that of 287 seconds, is drawn from observations made at the Havana, at the Pendulum Isles, on the east coast of Greenland, in Lat. 74° 5' and between Spitzbergen and Hammerfest, near the North Cape. According to professor Hansteen, this curve enters the continent of Europe between Archangel and Nova Zembla; and he crossed it in going from Moscow to Tobolsk, at 56° and 57° of East Lon. and 57° and 58° of North Lat.

The fourth curve, or that of 297 seconds, passes near Jamaica, where the oscillations were 294 seconds, passes through the north part of Britain, and enters Norway to the south of Bergen. It passes between Stockholm and Tornea, and thence by St. Petersburg and Moscow.

These four curves are the only ones that lay within the sphere of observation of professor Hansteen. The rest of the curves in the map were laid down by Captain Sabine, principally from his own observations and those of Humboldt.

Although the preceding investigations go far to point out the form of the isodynamical magnetic lines, yet much remains to be done before the blanks are filled up, and the lines traced round the poles of the southern hemisphere.

The most important and the most difficult part of the problem which still remains, is to ascertain the velocity with which these poles revolve; and we entertain sanguine hopes that, in consequence of the recommendation of Baron Humboldt, and the zeal of the Academy of Sciences of St. Petersburg, a regular system of observation will be immediately set on foot by the Russian government, to obtain an early solution of this great scientific question. The empire of Russia is actually traversed by two lines of the variation. One of these lines, according to the recent observations of Hansteen and Erman, passes between Mourum and Nijni-Novgorod, and the second some degrees to the east of Irkutsk, between Parchiuskaia and Torbinsk. It is proposed to determine with great precision every ten years the exact position of these two lines. Petersburg, Moscow, and Kasan are situated near the first line of no variation, which traverses Russia in Europe. Kiachta and VerkhnéOudinsk present advantages for the second line, which passes through Siberia. In the space of