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 the 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 had begun to lapse; especially since the general subject of magnetism continued from time to time to receive large and valuable accessions both in the line of theory and ex. periment. But terrestrial magnetism is a science of observation, in contradistinction to

a moment.

The sum of all seems to us to be, that the qualities of the orator were more transcendent then those of the statesman, and that his public character, when calmly considered, excites rather admiration than applause. The 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 intoo selfish a politician for the higher duties of dustry-no series of observations, however a ministerlong continued and exact, made at a single place, can add much to our knowledge of the highly intricate laws and relations which prevail in it. For this purpose the assemblage and comparison of observations, made in every region of the globe and extending order to master so large a subject, multitude over long periods of time, are requisite. In must be brought to contend with mass, combination 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 orderly and methodical arrangement which brings spontaneously into notice both their correspondences and their differences.

For similar reasons the progress of all sciences which are properly and purely sciences of observation, such as astronomy, meteorology, &c., has necessarily been hitherto more slow, and interrupted by longer

ART. VIII.-1. Allgemeine Theorie des Erdmagnetismus. Resultate aus den Beobachtungen des Magnetischen Vereins im Jahre 1838. Herausgegeben von C. F. Gauss und W. Weber. Leipzig, 1839. 2. Intensitas Vis Magnetica Terrestris ad Mensuram absolutam revocata. Auctore Carolo Friderico Gauss. Göttinge, 1833. 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 strikà perfectionner la connaissance du Mag- ing conclusion, may be instantly followed nétisme Terrestre par l'établissement des up, while the mind is excited and alert, by stations magnétiques et d'observations cor- others adapted to its verification or extension; respondantes. while, for corroborative observations or in4. Report of the Committee of Physics, interesting 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 observation omitted leaves a blank which never can be filled;-inaccurately or erroneously stated, it poisons the stream of know. ledge at its source, and exercises an influence the more baleful, as it tends, in proportion to its apparent importance, to

Graced as he was with all the power of words' his talents were neither for conducting an office nor managing a party-he was neither the sun to rule the day nor the moon to rule the night-but a meteor which astonished and alarmed mankind by its supernatural splendour, but left the world, when it expired, in deeper darkness than before.

AMONG the great branches of science which the present generation has either seen to arise as of new creation, or to spring forward by a sudden and general impulse into a fresh and more luxuriant state of development, there is none more eminently practical in its bearings

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 in 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 those 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 architecture from the rudest to the most refined that age admits.


Regarded as a branch of that great assemblage of facts and theories which relate to the physical constitution of this our planet the forces which bind together its mass, and animate it with activity-the structure

In erecting the pinnacles of this temple, the intellect of man seems quite as incapable 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,



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)-the science of ter- under the title of magnetic observations, restrial magnetism occupies a large and comes to be discussed whenever some labo highly interesting place. Its relations lie rious and self-devoted inquirer girds himamong those mysterious powers which seem self to the task of comparison and reducto constitute the chief arcana of inanimate tion. The instrumen's with which all the earlier, and many modern, magnetic observations have been made, were of rude construction, or otherwise incapable of yielding much accuracy. The effect of unknown change has thus in innumerable cases become entangled with presumed instrumental error, so as to render it very difficult to de. cide whether or not to retain, and how, if retained, to employ the observations so made.

nature, and its phenomena form a singular exception to the character of stability and permanence which prevails in every other department of the general subject. The configuration of our globe-the distribution of temperature in its interior-the tides and currents of the ocean-the general course of winds and the affections of climate-whatever slow changes may be induced in them by those revolutions which Geology traces Hitherto, 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, fafavours 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 same 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 to 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 alter materially, and the lapse of half a cen- to a comparatively recent period, are vitiated tury or a century to obliterate and com- by another source of error, arising from the pletely 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 greatly 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 attrac have 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 addestruction 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 self-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 element has been passing during the last two centuries. The result, apart from all theoretical considerations and ideas of poles, axes, &c., is most curious and instructive. The whole system of variation lines, with their intricate convolutions, loops, ovals, intersections and asymptotic branches, are seen to be sweeping westward—not however, as it were bodily, but each in its progress undergoing most singular modifications of form and flexure, and gliding by gradations, which it now becomes possible to trace, but which without such restorations would baffle every attempt of the imagination, through all varieties of conjugate oval, cusp, and node, in which the geometry of curves luxuriates. It would be interesting, but far beyond our limits, to show how beautifully this sort of moving magnetic panorama explains, or rather how easily it enables us to conceive, the puzzling facts presented by the history of the variation at particular spots :-by what a felicity of accident, for example, the whole mass of West India property has been saved from the bottomless pit of endless litigation by the invariability of the magnetic declination in Jamaica and the surrounding archipelago during the whole of the last century, all surveys of property there having been conducted solely by the compass (Robertson, Phil. Trans. 1806)-by what a curious absorption of a conjugate oval and transition to another

The variation chart of Halley had been hardly forty years completed when, by the effect of these secular changes, it had already become obsolete, and to satisfy the wants of navigation it became necessary to reconstruct it. This was performed by Messrs. Mountain and Dodson about the middle of the last century, and their labours are highly deserving of notice by reason of their having attempted to execute this task systematically for several equidistant epochs, viz., for 1711, 1722, 1733, 1744, by the aid of observations drawn from official and other records, which were furnished them in great abundance by the Commissioners of the Navy, and the East India, African, and Hudson's Bay Companies. Thus they expected to be enabled, by comparing the charts so obtained, to form a predicted chart for 1755; a bold and praiseworthy attempt, which, however, was baffled by the discordances offered by the observations before them, discordances owing doubtless to the causes above enumerated. They appear therefore to have given up this course in despair, and to have formed their final chart for 1756 in a way little calculat ed to inspire confidence, viz., by mixing to gether observations of different dates, and by the exercise of a pretty arbitrary discretion in accepting some and rejecting others. In this unsatisfatory state, the subject of system it has happened that the needle has the magnetic variation appears to have repassed, within the period of recorded obsermained unt 1811, when on the occasion vation in London and Paris, from 11o east of the true meridian to 24o west, having attained the former direction by a gradual movement eastward-there remaining a while stationary-thence receding with a westward movement to the direction last indicated, where it again became stationary about 1806 or 1807, and is now again on the move towards the east ;-by which curious changes taking place immediately under their eyes, the secular variation of the magnetic elements has been forced on the attention of the philosophical world-and we might specify a multitude of interesting cases of the same nature.

Mr. Hansteen declares himself in favour

a prize proposed by the Royal Danish Aca demy, M. Hansteen, whose attention had for many years been turned to the magnetic phenomena, undertook its re-examination, with a view to determine how far it might be possible to reconcile the observations accumulated up to that time with the supposition of two magnetic poles revolving round the pole of the world in indefinite periods, an opinion which had been defended by Euler, Churchman, and others or whether, as Halley had asserted, four such poles were necessary-or, lastly, whether any such suppo. sitions as to the revolutions of polar points be competent at all to represent the pheno

« ForrigeFortsett »