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him from conciliating and associating in and applications than that of Terrestrial his designs the humbler but still neces- Magnetism. It might naturally have been sary utilities of other men. He fancied he expected that the directness and importance could make a political clock which should go of these applications would have secured to by the mere force of the main-spring, with it, at all times, a more than ordinary share of out the help of cog-wheel, pendulum, or bal- attention, and at all events have preserved it ance-lhe consequence was, that his system, from that state of torpor into which, during whenever it was set a-going, ran itself out in the latter years of the eighteenth century, it a moment.

had begun to lapse ; especially since the genThe sum of all seems to us to be, that the eral subject of magnetism continued from qualities of the orator were more transcend time to time to receive large and valuable ent then those of the statesman, and that his accessions both in the line of theory and es. public character, when calmly considered, periment. But terrestrial magnetism is a excites rather admiration than applause. The science of observation, in contradistinction to generosity of his sentiments did not always one of experiment, and this character, along guide his practice; and the majestic stream with some remarkable peculiarities which it of his declamations for the rights and liber- possesses as such, sufficiently explain a ties of mankind was always accompanied by neglect that might otherwise appear singular, eddies and under-currents of personal inter- and even in some degree blameworthy. No est. He was too fine a genius for lower, and single observer, whatever be his zeal and in. too selfish a politician for the higher duties of dustry-no series of observations, however a minister

long continued and exact, made at a single Graced as he was with all the power of words— place, can add much to our knowledge of the

highly intricate laws and relations which his talents were neither for conducting an prevail in it. For this purpose the assemoffice nor managing a party-he was neither blage and comparison of observations, made the sun to rule the day nor the moon to rule in every region of the globe and extending the night—but a meteor which astonished over long periods of time, are requisite. In and alarmed mankind by its supernatural order to master so large a subject, multitude splendour, but left the world, when it expir- must be brought to contend with mass, comed, in deeper darkness than before.

bination and concert to predominate over extent and diffusion, and systematic registry and reduction to fix and realise the fugitive phenomena of the passing moment, and

place them before the eye of reason in that Ant. VIII.-- 1. Allgemeine Theorie des Erd- orderly and methodical arrangement which

magnetismus. Resultate aus den Beobach. brings spontaneously into notice both their tungen des Magnetischen Vereins im correspondences and their differences. Jahre 1838. Herausgegeben von C. F. For similar reasons the progress of all

Gauss und W. Weber. Leipzig. 1839. sciences which are properly and purely 2. Intensitas Vis Magneticæ Terrestris ad sciences of observation, such as astronomy,

Mensuram absolutam revocata. Auctore meteorology, &c., has necessarily been hi.

Carolo Friderico Gauss. Göttingæ, 1833. therto more slow, and interrupted by longer 3. Lettre de M. de Humboldt à S. A. R. Mgr. intervals of dormancy, than those in which

le Duc de Sussex, Président de la Société appeal can be made to experiment. An exRoyale de Londres, sur les moyens propres periment, if it lead to any new view or strik. à perfectionner la connaissance du May. ing conclusion, may be instantly followed nétisme Terrestre par l'établissement des up, while the mind is excited and alert, by stations magnéliques el d'observations cor- others adapted to its verification or extension; respondantes.

while, for corroborative observations or in4. Report of the Committee of Physics, in- teresting conjunctures, we must wait—a con.

cluding Meteorology, on the objects of dition especially adapted to blunt the keenScientific Inquiry in those Sciences. Ap-ness of inquiry and obscure the connections proved by the President and Council of of thought. An experiment mistated or mis. the Royal Society. London, 1840. interpreted, may be repeated, rectified, and

studied with better attention and success. An AMONG the great branches of science which observation omitted leaves a blank which nethe present generation has either seen to arise ver can be filled ;-inaccurately or erroneas of new creation, or to spring forward by ously stated, it poisons the stream of know. a sudden and general impulse into a fresh and ledge at ils source, and exercises an in. more luxuriant state of development, there is fluence the more baleful, as it tends, in none more eminently practical in its bearings proportion to its apparent importance, to

warp our theories, and thereby prevent or at the tall and spiry pine in graceful and unleast retard the detection of its faultiness. encumbered natural growth, but, like a

Nor does the progress of such sciences column built by men, ascends amid extranesuffer less from our ignorance of what is and ous apparatus and shapeless masses of mawhat is not of primary importance in the terials ; nor is that column in its fair and natural development of phenomena--of what harmonious proportions more different in its ought to be diligently recorded, and what aspect, when erect and complete, from what may be allowed to pass without notice. it was when so surrounded and overborne, Hence it happens that great masses of know. than such a theory, presented to us in its ledge are daily perishing before our eyes simplicity, from the tentative, transient and without the possibility of recovery, because, empirical conceptions which have helped to iu fact, our eyes are not open to them, and its construction. we have nothing to awaken our attention to In the science of Physical Astronomy their transient display. It is on this account the scaffolding has been long stripped away, that a theory is of'so much more consequence, and its theory stands august and stately, and forms in fact so much larger a part of with that air of nature which marks it as our knowledge in these sciences of observa- the intellectual shadowing forth of a sublime tion than in ihose conducted by the way of reality. In that of Terrestrial Magnetism, experiment. In the latter, facts are realities; a science which is not without its analogous they stand of themselves, may be reproduced, features, we are yet busied in building and touched, and handled, and admit us, as it pulling down, casting and recasting our were, by appeal to our senses, into the most design, piecing together our scaffolding, direct and intimate knowledge which we can and securing our foundations for a far greatattain of their efficient causes. To such sub. er and more massive edifice than was at stantial forms theories sit loosely, as an airy first contemplated. But already some porinvestiture, easily accommodating themselves tions have begun to assume a symmetry, to the changes of attitude and general growth and to convey to the experienced eye of that body they adorn and symmetrise ; glimpses, if not of the plan and dimensions, while, to the incoherent particles of historical at least of the general style and character of statement which make up the records of a the future whole ; glimpses, however, not science of observation, theories are as a obtained by viewing it from the lower ground framework which binds together what would of its first foundation, but by ascending to otherwise have no unity. They give to a a higher level, and surveying it from the collection of fleeting impressions the power ''coign of vantage' afforded by the more ad. of presenting itself to our intellect as an exist- vanced and rapid progress of its nearest reing whole. In these, then, it is perhaps not lated experimental science, Electro-dynausing too strong an expression to assert that mics, or from the commanding heights of the theory is the science. In it alone we Physical Astronomy, to which, as already must look for indications that we are on the remarked, it stands in no remote connection safe track towards the detection of efficient of analogy. To the former of these it owes causes—from it only we can receive hints to its essential character and the direction of guide us in our choice both of things to be its leading lines, since it is there we are to observed, and of the best and most available look for the vera causa of the Newtonian mode of making and recording our observa- philosophy. From the other it has already tions—and to it we must look for our only begun to borrow largely, in point of style means of reproducing the past, and recover- and manner, in the adoption of its mode of ing the lost history of bygone time. It is treating the complicated problems which when they first become capable of perform- occur in the estimation of its resultant forces ing this office, that theories begin to assume on the most general suppositions as to the their places as corner-stones in the temple distribution of the magnetic power through of science-a building always altering, al- the substance and over the surface of the ways enlarging, and combining in every age, globe. in its several departments, every form of Regarded as a branch of that great asarchitecture from the rudest to the most re. semblage of facts and theories which relate fined that age admits.

to the physical constitution of this our planet In erecting the pinnacles of this temple, the forces which bind together its mass, the intellect of man seems quite as incapable and animate it with activity—the structure of proceeding without a scaffolding or of its surface-its adaptation for life-and circumstructure foreign to their design, and the history of its past changes-the nature, destined only for temporary duration, as in movements, and infinitely varied affections the rearing of his material edifices. A of the air and ocean, and all which our conphilosophical theory does not shoot up like tinental neighbours understand by their term,

19

VOL. LXVI.

same

physique du globe-(a phrase of which our can be more disheartening than the mass * terrestrial physics' is rather a faint and of confusion and apparent error which, inexpressive reflection)-he science of ter- under the title of magnetic observations, Testrial magnetism occupies a large and comes to be discussed whenever some laboe highly interesting place. Its relations lie rious and sell-devoted inquirer girds him. among those mysterious powers which seem self to the task of comparison and reducto constiiute the chief arcana of inanimate lion. The instrumen's with which all the nature, and ils phenomena form a singular earlier, and many modern, magnetic obserexception to the character of stability and vations have been made, were of rude con. permanence which prevails in every other struction, or otherwise incapable of yielddepartment of the general subject. The ing much accuracy. The effect of unknown configuration of our globe-the distribution change has thus in innumerable cases beof temperature in its interior, the tides and come entangled with presumed instrumental currents of the ocean—the general course error, so as to render it very difficult to de. of winds and the affections of climate-what- cide whether or not to retain, and how, if ever slow changes may be induced in them retained, to employ the observations so made. by those revolutions which Geology traces Hitherio, however, when it has been possi--yet remain for thousands of years ap- ble to apply a correction for lapse of time, preciably constant. The monsoon, which the result has been), generally speaking, fa. favours or opposes the progress of the steam. vourable to the exactness of even very early er along the Red Sea, is the same which magnetic determinations, at least on land; wafted to and fro the ships of Solomon. so that such early records, like the ancient Eternal snows occupy the same regions, eclipses in astronomy, become, as time flows and whiten the

mountains—and on, of great importance and value, which springs well forth at the same elevated tem. will not fail to be felt hereafter, when theory perature from the same sources now as in shall find itself strong enough 10 leap the the earliest recorded history. But the mag. interval, and declare the magnetic state of netic state of our globe is one of swift and the globe a century or two back. But all ceaseless change. A few years suffice to earlier observations at sea, or rather all up alier materially, and the lapse of half a cen- 10 a comparatively recent period, are vitiated tury or a century to obliterate and com- by another source of error, arising from the pleiely remodel, the form and situation of iron of the ship, and that in a manner the those lines on its surface which geometers more hopelessly irrecoverable, because the have supposed to be drawn in order to give error so induced is not constant, but varies a general and graphical view of the direction not only with every change of geographical and intensity of the magnetic forces at any situation, but with every alteration in the given epoch.

position with respect to the points of the It is this feature which constitutes, in fact, compass in which the ship is lying at the the great and peculiar difficulty of the sub- moment of observation. Fortunately for ject. Were the magnetic forces at every magnetic science, this vexatious source of point of the earth's surface invariable, like error, first detected by Captain Flinders, has the force of gravity, or nearly so, we should been great!y alleviated, and in ordinary long ago have been in possession—and that cases nearly destroyed, by Mr. Barlow's without extraordinary effort—of complete, or ingenious adaptation of a compensating iron, nearly complete, magnetic charts. The re- purposely placed near the compass so as to port of every seaman and traveller would counteract, by an equal and opposite attrachave added something permanent to our ac- tion, that of all the rest of the iron in the cumulating stock of knowledge, and truth vessel. And even in what might at first would have emerged, even from inaccurate appear the desperate case of a vessel built determinations, by the conflict and mutual entirely of iron, the recent elaborate and ad. destruction of opposite errors. As it is, the mirably conducted inquiries of Mr. Airy case is widely different. The changes are have furnished the means of reducing to a so rapid that it becomes necessary to as- mere trifle, or annihilating altogether, the sume epochs, which ought not to be more complicated errors arising from two distinct than ten years apart, to which every observa. sources of magnetism: the one transient, tion should be reduced. But to do this, it induced in the soft iron of the vessel by the is requisite to know the rate of change for each earth's influence :-the other permanent, locality ; information we are so far from originating in the rolled and hardened plates possessing that there are great regions of the and other masses deviating from the condi. globe over which we do not even know in tion of pure soft iron, employed in its conwhat direction the change is taking place. struction.

For want of this information, nothing In neglect, or in spite of these difficulties,

the exigences of navigation have necessitated ploration and discovery, forming part of by the construction, from time to time, of charts for the most extensive combined scientific expressive of the variation of the compass, operation the world ever witnessed, has re. or the angle by which the needle declines cently left our shores. from the true meridian at every point of the earth's surface; whence the term declination

· The nice determination of this and several now used instead of variation. The first ed for a remote posterity. All that we can hope

other particulars in the magnetic system is resery. chart of this sort, based upon the idea of to do is to leave behind us observations that may employing, for their construction, a series of be confided in, and to propose hypotheses which curves drawn through the points of equal after ages may examine, amend, or refute. Only declination, (in itself a scientific invention of here I inust take notice to recommend to all mas.

ters of ships, and all other lovers of natural truths, no mean order,) is due to Halley. It was that they use their utmost diligence to make, or constructed by him with infinite labour and procure to be made, observations of these variations research, by the collection of all such observ- in all parts of the world, as well in the south as ations as that age had furnished. This chart, East India commanders), and that they please to

the north latitude (after the laudable manner of our and the very remarkable papers by which its communicate them to the Royal Society in order to communication to the Royal Society was leave as complete a history as may be to those that preceded, (in 1683 and 1692,) to say nothing are hereaster to compare all together

, and to comof his own personal labours and devotion in plete and perfect this abstruse theory.' his memorable voyages of magnetical discovery to St. Helena, must ever form a leading a passage from the pen of our illustrious

We may refer with complacency to such epoch in the science of terrestrial magnet. ism, and justly entitle him to be regarded as moment that his brother officers of a later

countryman, himself

a seaman,* at the the father and founder of that science, con.

age, Ross and Crozier, on their adventu. sidered as a body of knowledge bound to.

rous voyage,

and imbued with his o:vn spirit, gether by laws and relations. To him we owe the first appreciation of making observations of ihese variations in

are engaged in realising his anticipations, the real complexity of the subject, and the all parts of the world,' and communicating first attempt at a rational coup-d'ail of the whole in the announcement of a theory junction with the directors of our magnetic

them to the Royal Society,'t and in con. which, though rude and unabstract in the observatories, maintaining and perpetuating form of its statement, and rendered thereby

our national claim to the furtherance and liable to obvious and fatal objections inlimine, has at least the merit of affording a handle perfecting of this magnificent department of for exact reasoning and distinct comparison

physical inquiry.

The theory, or rather hypothesis of Halley, with facts; joined to that of giving a not

to which reference is made above-and unplausible account (the postulates being which regards this our globe as a great granted) of several important features of the piece of clockwork, sphere within sphere,

. is account for the existence of not two only, by which the poles of an internal magnet but four points, or rather regions of appa- but unknown period-may be regarded, in

are carried round in a cycle of determinate rent convergence of the magnetic needle, iwo in each hemisphere, and for the changes netic phenomena, in the light of a specimen

of the secular variations of the mag

respect going on in every part of the globe, in the

of that sort of scaffolding to which we have direction assumed by it with respect to the

With such additional meridian, both which, the latter as an unde figuratively alluded. niable physical fact, the former as an una

epicycles as the progress of magnetical disvoidable conclusion from the course of the covery might necessitate from time to time, variation lines in his chart, are broadly de

it might serve to represent several of the clared by him in these papers. It is wonder. leading phenomena-much in the same way

as the Ptolemaic orbs served to convey ful indeed, and a striking proof of the pene something more than à vague and general tration and sagacity of this extraordinary idea of the celestial movements. But even man, that, with his means of information, he

as the rude and cumbrous celes:ial mechan. should have been able to draw such conclu- ism of Hipparchus and his successors has sions, and to take so large and comprehensive a view of the subjeci as he appears to tapered into the lofty and forid . mécanique sive a view of the subject as he appears to céleste' of modern times, so the pursuit of have done. The following passage in his

those slow and intricate changes in the paper of October 19, 1692, will be consider. ed as having especial interest at the present time, when the spirit of inquiry is excited on

* Halley held a captain's commission in the

navy: the subject to a degree never before known, + Their observations up to the end of 1839 aro and when an expedition of magnetical ex• already received.

magnetic elements of each particular ter-, mena. His work, Ueber den Magnetismus restrial locality which presented themselves der Erde, published in 1819, is in every to Halley under the aspect of mechanical way most remarkable. revolutions, begins to assume, in the eyes of With indefatigable labour he has traced modern theorists, under the influence of back the history of the subject, and filled up more general views as to the origin and the interval from Halley's time, and even distribution of the magnetic forces, the sem- from an earlier epoch(1600), with charts blance of those ever varying and never constructed for that epoch, and a great overstepping, those inherently equipoised many intermediate ones, up to 1800, so as and sell-bridled oscillations which, so far as to present before us in one view, as far as it we can see, afford the best expression of the can now be done, the succession of states or planetary movements.

phases through which this elernent has been The variation chart of Halley had been passing during the last two centuries. The rehardly forty years completed when, by the sult

, apart from all theoretical considerations effect of these secular changes, it had al- and ideas of poles, axes, &c., is most cuready become obsolete, and to satisfy the rious and instructive. The whole system wants of navigation it became necessary to of variation lines, with their intricate conreconstruct it. This was performed by volutions, loops, ovals, intersections and Messrs. Mountain and Dodson about the asymptotic branches, are seen to be sweepmiddle of the last century, and their labours ing westward—not however, as it were bodiare highly deserving of notice by reason ly, but each in its progress undergoing most of their having attempted to execute this singular modifications of form and flexure, task systematically for several equidistant and gliding by gradations, which it now epochs, viz., for 1711, 1722, 1733, 1744, becomes possible to trace, but which without by the aid of observations drawn from such restorations would baffle every attempt official and other records, which were fur- of the imagination, through all varieties of nished them in great abundance by the conjugate oval, cusp, and node, in which the Commissioners of the Navy, and the East geometry of curves luxuriates. It would be India, African, and Hudson's Bay Compa- interesting, but far beyond our limits, to nies. Thus they expected to be enabled, by show how beautifully this sort of moving magcomparing the charts so obtained, to form a netic panorama explains, or rather how easily predicted chart for 1755 ; a bold and praise- it enables us to conceive, the puzzling worthy attenipt, which, however, was baffled facts presented by the history of the variation by the discordances offered by the observa- at particular spots :-by what a felicity of actions before them, discordances owing doubt-cident, for example, the whole mass of West less to the causes above enumerated. They India property has been saved from the bot. appear therefore to have given up this tomless pit of endless litigation by the invarcourse in despair, and to have formed their iability of the magnetic declination in Jamaifinal chart for 1756 in a way little calculat. ca and the surrounding archipelagó during ed to inspire confidence, viz., by mixing to the whole of the last century, all surveys gether cbservations of different dates, and of property there having been conducted by the exercise of a pretty arbitrary dis- solely by the compass (Robertson, Phil. cretion in accepting some and rejecting Trans. 1806)—by what a curious absorption others.

of a conjugate oval and transition to another In this unsatisfatory state, the subject of system it has happened that the needle has the magnetic variation appears to have re passed, within the period of recorded obsermained until 1811, when on the occasion of vation in London and Paris, from 11° east a prize proposed by the Royal Danish Aca of the true meridian to 24° west, having at. demy, M. Hansteen, whose attention had tained the former direction by a gradual for many years been turned to the magnetic movement eastward—there remaining a phenomena, undertook its re-examination, while stationary---thence receding with a with a view to determine how far it might be westward movement to the direction last possible to reconcile the observations accu. indicated, iv here it again became stationary mulated up to that time with the supposition about 1806 or 1807, and is now again on of two magnetic poles revolving round the the move towards the east ;-by'which curipole of the world in indefinite periods, an ous changes taking place immediately under opinion which had been defended by Euler, their eyes, the secular variation of the magChurchman, and others—or whether, as netic elements has been forced on the atten. Halley had asserted, four such poles were ne. tion of the philosophical world—and we might cessary—or, lastly, whether any such suppo specify a multitude of interesting cases of the sitions as to the revolutions of polar points same nature. be competent at all to represent the pheno. Mr. Hansteen declares himself in favour

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