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1829.)
Col. Macdonald on the Two Magnetic Poles.

१३ Sir Lewis Dyve was one of the mem- than the science of magnetic variation, bers for Bridport in Dorsetshire. On on which a series of papers appeared in the assembling of the Long Parliament the Gentleman's Magazine." Permit in 1640, he was again relurned* ; but me to add one, including some farther was afterwards " disabled," probably progress, sanctioned by observations in 1643, when several members were and experiments. The advancement under that term espelled, for their of a science still in its infancy, and on then holding commands in the King's the establishment of which navigation army.

and commerce mainly depend, is much Although Sir Lewis does not appear retarded by the erroneous supposition as a speaker in Parliament himself, of the existence of a multiplicity of yet we find he was active in 1641 in magnetic poles. As it has been republishing the speech which his half- cevily stated with confidence that the brother Lord Digby had made against alleged position of a north-east pole the condemnation of the Earl of Siras. has been confirmed by the observations ford, and which was afterwards pub- of an eminent philosopher in a remote licly burnt by the common hangman. quarter of Eastern Russia, it is the obIt was delivered on the 21st of April ject of this paper 10 disprove the supe that year, and on the 15th of July ine position, and io altempi to make out House resolved, " that Sir Lewis Dyve ihat there can be but two magnetic and John Moor, as also Thomas Par. poles, viz. the north-west and southslow, printer of the said speech, are east; that is to say, one in each hemidelinquents, in printing and publish- sphere. ing thereof." Lord Digby, in his “ A po- It is necessary to give an equatorial logy,” issued in Jan. 1641-2, staies, projection of the sphere, in order to that he “ did not only find that it was elucidate clearly the object in view, unsaithfully reported and uncharitably and the demonstration will, cæteris represented, but was informed that parilius, be equally applicable to the copies went abroad of it, so falsely and southern hemisphere. It may be premaliciously collected, as made the viously requisite to observe, that on whole speech a justification of my Lord several paris of the earth, in whatever of Straflord's innocence; and Sir Lewis direction they are approached, the Dyve, having beard of such a copy in needle is attracted by magnetic strala. the house of a citizen of good quality, In the northern hemisphere, these hare where he heard me mentioned as a a south polarity above, and a norih beperson fit to have his name fixed upon low, with a reverse effect in the other posts, ibat it might be torn 10 pieces hemisphere. The iron and guns of by the people, upon that reason ear- ships act similarly, in occasioning the nestly desired me to give him a true local attraction of the needle, on the copy of what I had said in that argn- due knowledge and application of ment, which I did; and he forth with which life and property greatly depend ; zare directions for the printing of it, and this may induce me hereafier to without any privity of mine."

give you my studied view of so very

J. G. N. important a branch of magnetism. as (To be continued.)

one instance of local terrestrial attrac

tion, the variation at the Falkland MR. URBAN,

Summerlands, Exe. Islands has altered only a degree and ter, July 1, 1829.

a half since it had been first observed

there; and this small attraction is to "HE centenary of your valuable

be ascribed to the constant movement work has nearly arrived; and be

of the north-west pole eastward, and ing peculiarly distinguished by ancient of the south-east westward, at the rate lore, withoui excluding useful scienti- of half a degree annually, and amountfic disquisition, a complete set, when ing only to a few miles, reckoned in obtained, constitutes a desirable article

the high latitude of the position of the in every seleci library: Few subjects eccentric curves in which they maniare of inore real national importance festly inove. Eminent philosophers List of that Parliament in Cobbett's

have situated each lis pole in the Parliamentary History: the list of Burgesses south-west quarter, in order, by their in Hutchins's Dorsetshire, in which the two supposed aciion, io account for the former elections of Sir Lewis are found, nearly stationary variation; but celegives other names under 15 Car. I.

brated navigators, who have approached

24

Col. Macdonald on the Two Magnetic Poles. [July, the supposed sites of these poles, havé tous poles assigned in the northern not found any real indication of their hemisphere, by great philosophers, in existence.

support of their relative theories; and In the following Figure, projected I shall endeavour to shew, that they round the earth's north pole to the are devoid of magnetic effect, and conparallel of 70°, are situated the gratui- sequently of existence.

Line of no Variation in 1657.

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LONDON, 51°31'. Over N, the north pole of the earth, a curve probably more eccentric than is drawn LNS, the ineridian of Lon- P***P. In order to discover the nadon, being the line of no variation in ture and position of this curve, it is 1657, because the needle at L, London, now well understood, that at intervals pointed due north to the magnetic pole of a few years, the site of the pole must S, corresponding to its real place with- be found at the positions a, by means in the earth. At P, on the west side of the dipping-needle; and thus also of the figure, is situated the north-west its real rate of movement will be asmagnetic pole, by approximations, in certained. This now can be effected the year 1820, at the intersection of easily, by the short run from the 70° north latitude and 100° west longi- mouth of the Mackenzie, or CopperLude. The pole is moving eastward in mine River.' After former repeated. 1829.) Col. Macdonald on the Two Magnetic Poles.

25 attempts, the enterprising Capiain Ross equator, the west variation increases, has but a slender chance of getting and would altain its maximum at the ihrough Regent's Channel, convignous south pole of the earth. Moving 10 the magnetic pole. This spirited thence, on the same meridian, the narigator will try 10 get through one variation would become nothing, in ol:he large channels on the north side approaching on the west side of the of Barrow's Siraits, and if he finds an earth to the north-west pole. The open sea, he may plant the British flag celebrated magnetician, Mr. Churchon the pole of the earth; or he may man, supposed that the pole moved sleam along the north side of the Geor- under a parallel of latitude, as Pokp. gian Islands, and find a passage down Were this the case, ihe present west io Behring's Straits. No time ought variation would increase manifestly, to be lost in finding the poinis t, be- till the pole arrived at the tangetical cause the pole is moring on 10 the point m, when the angle NL in would inaccessible regions. li is of the express the angle of west variation. most essential moment to navigation Afier this, it would decrease to noand compierce, that the place of the thing on the meridian of London, as in pole should at all times be known, in 1657. But as the variation was at its order to calculate the variation, and to maximum in 1817, or 24° 17', and has find the local attraction of a ship, been since decreasing, it is evident which is the difference between the that it cannot be moving with its pole, observed and calculated variation, al. under the parallel PB m. The pole lowing for a small atiraciion by the canvot be moving in a straight line, or more remote magnetic pole.

in a curse, under the meridian of no Pw N is the meridian of the north- variation PNP, because all living unwest line of no variation, at the above der such meridion would have no vilperiod; and Ny P is the north-east riacion at any time, a thing not a fact. line, running through western Russia The pole cannot be nioving in a and along ihe Coromandel coast. On straight line on the north or south side this meridian in the southern hemi- of the pole of the earth, as, for insphere, a little to the south of the stance, in the line Pro; because those equator, a west variation arises, be- living at P and o would always have cause the south extremity of the needle the same variation, rPN or roN; there is attracted eastivard by the excepting when the variation would south-east pole, causing the rigrih end vanish, when the pole was direcily to incline westward. For the same under their situation, P ani! o. On reason, in moving southward from the every other situation on this line, such

Captain Ross, having determined once more to attempt the discovery of the NorthWest Passage, lately equipped a steam-vessel, called the Victory, entirely at his own expence. The steam power employed is on a wholly new principle; being so contrived as to combine every advantage of steam-power, with perfect capability as a sailing vessel. The boilers in use occupy so small a space, that they are fixed between the engines; the consumption of fuel is one-half, and the weight of the engines only one fourth, of those generally in use. Another advantage is, that a chimney may be dispensed with, which leaves the deck, masts, and rigging wholly unencumbered. The last intelligence from Captain Ross was dated Loch Ryan, June 14th and 15th. It appears that the engineer of the steamer was so severely hurt by the rod of the piston, that Captain Ross was obliged to amputate his arm. On joining the John (a vessel that was to have accompanied him) Captain Ross found that great discontent prevailed among the crew of the vessel; and upon his going on board, the crew individually refused to heave the anchor. Captain Ross then goes on to state," Oo my saying that my meu (i. e. the crew of the Victory) should do it for them, the cowardly vagabonds took to the boats, and landed amidst the hisses and execrations, not only of the gallant crew (who gave three cheers, and said • Let us go without them'), but of the villagers, who assembled to witness the landing. A scufile took place between the captain and the crew ; and in their attempting to take one of our boats to escape with, one man was knocked overboard; but no lives were lost. I immediately decided op removing what stores were necessary to complete us from the Johu, and to proceed without her; which has, I am happy to say, given my brave fellows universal satisfaction. They answered my determination with three cheers, and declared they would follow and stick to me wherever I went. We are all in the highest spirits ; the wind is fair, the eugine, bellows, and boiler, are all in repair, and the anchor is now up. Farewell!" GENT. MAG. July, 1829.

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26

Col. Macdonald on the Two Magnetic Poles. [July, as ļ, the variation would be east or when Captain Parry crossed its meri. west, according as the moving pole dian. Had such pole existed, the happened to be east or west from the needle would have pointed to it on this position r, where there would be 110 meridian, supposing it to be the real variation, when the pole would be magnetic pole. The needle did not directly under such site. If the line point due south, till the discovery-ships Po be supposed to be continued east- arrived on the meridian of 100° west ward and westward, to where the longitude ; and had the Professor's south-east pole begins to set sensibly, pole exisied, the needle, infuenced by the variation on such continued line both poles, wonld have given a variawould be always the same, which is a tion of probably 145o east, instead of case not known to exist.

It must,

180° on the real meridian, or line of from these statements, be concluded, no variation. Monsieur Biot, a philothat the magnetic poles move in some sopher of considerable eminence, bas eccentric curve, such as P*** P. located a magnetic pole in 70° north

Churchman, who made the period latitude and 720 west longitude; and of a revolution of the pole 1096 years, the great Dr. Halley, second only 10 instead of what it appears to be, vis. Newton, placed a pole nearly in the 720, situated his norih-west pole in same situation in Baffin's Bay. It is 1340 west longitude, and 580 north only necessary to say, that the alleged latitude, or nearly at c of the figure. sites of these supposed poles have been This situation on the west coast of explored, without finding any trace of North America, has been frequently their reality. At the south east cape visited by navigators, without any indi of Greenland, iu latitude 70° and loncations of such pole by the dipping- gitude 23" west, and nearly at K of the needle; and were it real, the horizon- figure, Professor Krufft situates his tal needle would have pointed south, north-west pole. In frequently crosswhen passing through the Sound close ing the meridian of this imaginary to the south of iis imagined site. The pole, and so near that the horizontal eminent mathematician, Loler, placed and dipping needle must have been his north-west pole at e of the ligure, acted on, no such effect appeared. If in 76° norih latitude, and 960 west a line be drawn from London to the from Teneriffe, or nearly in 113° west place of four of these poles, it will pass longitude. This position, about seven much to the north and east sic of the and a half degrees from the real mag. place of the real north-west pole P; netic pole, and north-west from ii, and a line from London to Biot and was ingeniously imagined, and enabled Hansteen's pole, will pass a little 10 that great man to account tolerably for the southward of it. 'On magnetic the variation in Europe and America. principles, therefore, the needle ai LonCaptain Parry's first voyage completely don oughi 10 point to the eastward of disposes of this pole, as Winter-Har- the real pole. But how stands the bour in 740 47' 13", and 110° 49' lon- fact? It is, that by means of the co. gitude, was within 1° 12' 47" of the latitude of London, the co-latitude of latitude of Euler's pole, and but a little the pole, and the difference of longi. on the east side of its meridian. Now tude, the calculated is 1° 13' less than it is evideni, that thus situated, the the observed variation; or, in oiher north end of the needle must have words, the needle points 10 1° 13' 10 pointed to such pole; whereas there the southward of the real magnetic was a variation of 127° 47' 50" east, meridian ; because the south-east magshewing that the north extremity of neric pole, acting on the south end of the needle was attracted by the real the needle inversely as the square of north-west magnetic pole. Professor the distance, aliacts it eastward, and Hansteen situates his pole in 1709, increases the calculated to the observed 19° 43' from the north pole of the variation. earth, and in longitude 259° 58' east. The distinguished authors mentionHe makes it to move east ten or i welve ed did not, in point of fact (with the minutes annually. Its place is nearly exception of Halley and Hansteen) at a in the figure. From 1709 10 1819, suppose the existence of more poles fisiy years, at the rate of twelve mie than one in each hemisphere; and they nutes of annual movement, would placed their pole or poles so as to corsituate this pole in 90° west longitude, respond with their respective theories. and 79° 13' of latitude, at the period On the east side of ihe meridian of

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1829.] Col. Macdonald on the Two Magnetic Poles.

27 London Dr. Halley situated his second this place, and the east variation arising pole, in 76° 30' north latitude, and 30° from its position, is much diminished east longitude. Captain Parry passed by the action of the south-east pole, within a few meridional degrees of still wearer to the meridian of the above this position ; and if such pole had town in East Siberia. This would been there, the north end of the needle render the variation very little, but still must have been attracted by it into a it could not be ascribed to the imaconsiderable east variation; instead of gined pole lying on the west side of which, it continued west.

Other na

The meridian of Irkutsk. All over the vigators passed near to the imagined oriental quarter, and considerably besite of this north-east pole, without yond the equator, the variation is little, perceiving any symptoms of its actua- on account of the manifest counteraclity. Halley's inaginary pole is placed tion of the two poles, on the same side in the figure at H. We have one other of the meridian of places under the pole to dispose of, which is the learned above magnetic circumstances. Sup. Professor Hansteen's, said to be in a posing the existence of a pole at h, 'it situation where it is utterly impossible is evident, on known magnetic printo approach it, viz. in 85° 49' north ciples, that the needle at London could latiiude, and 101° 30' east longitude; not point to the pole at P. It may

be being only 4° 11' from the north pole sufficient here to mention the result of of the earth, and nearly at h in the experiments made with two magnets figure. In Captain Parry's last publi- of equal power applied to the place of cation, a small decrease of the west the real and of the supposed pole, in variation, experienced in proceeding reference to a sensitive needle resting to Spitzbergen, is ascribed to the in- on the place of London. The variafiuence of this supposed magnetic pole tion given varied a few degrees, as in the north-east quarter. Supposing might be expected; but the medium a ship to move eastward on any parallel gave the angle L N n as the variation : of latitude, as that of 80° for instance,

but as the needle at London points in aad to arrive at 1 of the figure; here an angle somewhat greater than the the west variation would be the angle calculated variation, NLP, it amounts NIP, formed by the magnetic meri- to positive demonstration that the dian IP with the meridian IN, of the norih-west is the only magnetic pole place of observation. Let the ship in the northern hemisphere, and simimore on 10 2, where the variation N2lar reasoping applied to a similar figure will be manifestly less than that at 1. for the southern hemisphere, would, At 3, the variation will be still less; mututis mutandis, yield an equally conand at P of the meridian NyP, or clusive result. eastern line of no variation, it will be On the site of the magnetic pole the bothing; because the north pole of the dipping needle will stand perpendicucanh, N, and the real north-west pole, lar, in continuation of the semi-diameP, on the west side of the figure, are

ter of the earth, and on some part of under one and the same meridian, wbich, within the earth, the real pole, PwXyP. After passing this meridian, or magnetic power, is situated. After an east variation would arise ; and much consideration, it occurred to me which, at 4, would amount to the that the depth of the pole within the apgle P4N. At 5, the variation would hollow sphere of the earth, might be be greater; and at o, it would be indi- calculated trigonometrically. The difrated by the angle Pon. Were the ference of latitude between the place Professor's the only pole in the northern of the pole on the surface, and the bemisphere, the variation at o would place where a dip is taken, gave the be only the small angle Noh. The angle at the centre. The complement scientific world are greatly indebted to of the angle of the dip 10 90° gave Professor Hansteen for having lately the acute angle at the circumference. made a laborious journey into Siberia, Having thus the three angles of a in order to elucidate important poinis triangle within the earth, and the in the useful science of magnetic varia- radius as one of the sides, the part of tion. He is said to have made salis- the other radius, intercepted between faciory observations at Irkutsk, in lati- the true place of the pole and the iude 520, and longitude 1049 east. centre of the earth, was calculated. The north-west magnetic pole is consi- By subtracting this from the semi-diaderably to the east of the meridian of meter on which the pole is situated,

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