Letter from Baron von Humboldt to His Royal Highness the Duke of Sussex, K.G., President of the Royal Society of London, on the Advancement of the Knowledge of Terrestrial Magnetism, by the Establishment of Magnetic Stations and corresponding Observations.

We translate this letter from Schumacher’s Astronomische Nachrichten, No. 306, which has been kindly communicated to us for the purpose.

Sir,

THE generous interest taken by Your Royal Highness in the advancement of human knowledge, encourages me to hope for the favourable reception of the request which with respectful confidence, I now venture to address to you. I take the liberty of soliciting your attention to the labours requisite for the investigation, by precise means, almost constantly employed, of the variations of terrestrial magnetism.

By obtaining the cooperation of a great number of zealous observers, provided with instruments of similar construction, M. Arago, Mr. Kupffer, and myself have succeeded in the last eight years in extending these researches over a very considerable part of the northern hemisphere.

Permanent magnetic stations being now established from Paris to China, following towards the east the parallels from 40° to 60°, I feel myself justified in soliciting, through the intervention of Your Royal Highness, the powerful cooperation of the Royal Society of London, to sanction this enterprise, and also to promote its success by the establishment of new stations, as well in the vicinity of the magnetic equator as in the temperate part of the southern hemisphere.

An object which is equally important whether it be considered in connexion with the physics of the earth or the improvement of nautical science, has a double claim upon the attention of a Society, which has from its commencement, with constantly increasing success, cultivated the vast field of the exact sciences.

Our information respecting the progressive development of the knowledge which we possess of terrestrial magnetism must be indeed imperfect, if we are ignorant of the numerous valuable observations which have been made at different epochs, and are still being made, in the British isles, and in various parts of the equinoctial zone subject to the same empire.

Our present object is to render these observations more useful, that is, better adapted to manifest great physical laws, by coordinating them according to a uniform plan, and connecting them with the observations now in progress upon the continent of Europe and Northern Asia.

Having been much occupied during my travels in the equinoctial regions of America, during the years 1799—1804, with the phænomena of the intensity of the magnetic forces, and the inclination and declination of the magnetic needle, on my return to my own country I conceived the design of examining the progress of the horary variations of the declination, and the perturbations to which it is liable, by employing a method which, I believe, has never yet been followed upon an extensive scale.

In a large garden at Berlin, during the years 1806 and 1807, particularly at the period of the equinoxes and solstices, I measured the angular alterations of the magnetic meridian, at intervals of an hour, often of half an hour, without interruption during four, five, and six days, and as many nights.

Mr. Oltmanns, whose numerous calculations of geographical positions have recommended him to the notice of astronomers, kindly shared with me the fatigues of these labours.

The instrument which we employed was a magnetic telescope (lunette aimantée) of Prony, capable of being reversed upon its axis, suspended according to the method of Coulomb, placed in a glass frame, and directed towards a very distant meridian mark, the divisions of which, illuminated during the night, indicated even six or seven seconds of horary variation.

In verifying the habitual regularity of a nocturnal period, I was struck with the frequency of the perturbations, especially of oscillations the amplitude of which extended beyond all the divisions of the scale, and which occurred repeatedly at the same hours before sunrise, and the violent and accelerated movements of which could not be attributed to any accidental mechanical cause.

These vagaries of the needle, the almost periodical return of which has recently been confirmed by Mr. Kupffer in the narration of his Travels in the Caucasus, appeared to me the effect of a reaction of the interior of the earth towards the surface; I should venture to say, of magnetic storms, which indicate a rapid change of tension.

From that time it has been my desire to establish on the east and west of the meridian of Berlin apparatus similar to my own, in order to obtain corresponding observations made at great distances and at the same hours; but the political tempest of Germany, and my hasty departure for France, whither I was sent by the Government, delayed for a length of time the execution of this project.

Fortunately my illustrious friend M. Arago, after his return from the coasts of Africa and the prisons of Spain, undertook, I think about the year 1818, a series of observations upon magnetic declinations at the Observatory of Paris, which, made daily at intervals uniformly fixed, and continued upon the same plan to the present day, are considered, with regard to their number and mutual connexion, superior to everything that has been attempted in this kind of physical investigations.

Gambey’s apparatus, which is employed, is of perfect execution.

Provided with micrometers and microscopes, it may be employed with more certainty and convenience than Prony’s instrument, which is attached to a strong magnetized bar of 20 [Formel] inches in length.

During the progress of these observations M.

Arago has discovered, and proved by numerous examples, a phænomenon which differs essentially from the observation made by Prof.

Hiorter at Upsal in 1741.

He has discovered not only that the Auroræ boreales disturb the regular progress of the horary declinations there when they are not visible, but also that early in the morning, often ten or twelve hours before the luminous phænomenon is developed in a very distant place, its appearance is announced by the particular form presented by the curve of the diurnal variations, that is, by the value of the maxima of elongation of the morning and night.

Another new fact was manifested in the perturbations.

Mr. Kupffer having established at Cazan, nearly the eastern limit of Europe, one of Gambey’s compasses, exactly similar to that employed by M.

Arago at Paris, the two observers were convinced by a certain number of corresponding measures of horary declination, that, notwithstanding a difference of longitude of more than 47°, the perturbations were isochronous.

They were like signals which from the interior of the earth simultaneously arrived at its surface on the borders of the Seine and the Wolga.

When in 1827 I again fixed my residence at Berlin, my first care was to renew the series of observations which I had made at short intervals during the days and nights of the years 1806 and 1807.

I endeavoured at the same time to generalize the means of simultaneous observations, the accidental employment of which had just produced results so important.

One of Gambey’s compasses was placed in the magnetic pavilion, in which no portion of iron was introduced, which had been erected in the middle of a garden.

Regular observations could not commence till the autumn of 1828.

Being called, in the spring of 1829, by His Majesty the Emperor of Russia, to undertake a mineralogical tour in the North of Asia and on the Caspian Sea, I had an opportunity rapidly to extend the line of stations towards the east.

At my request the Imperial Academy and the Curator of the University of Cazan erected magnetic houses at St. Petersburgh and Cazan.

In a committee of the Imperial Academy, at which I had the honour of presiding, a discussion took place on the immense advantages, with regard to our knowledge of the laws of terrestrial magnetism, presented by the vast extent of country limited on one side by the curve without declination of Doskino, (between Moscow and Cazan, or with more precision, according to M.

Adolphe Erman, between Osablikowo and Doskino, in lat. 56° 0′, and long. 40° 36′ east of Paris,) and on the other, by the curve without declination of Arsentchewa near Lake Baikal, which is believed to be identical with that of Doskino, with a difference of meridians of 63° 21′.

The Imperial department for Mines having generously concurred in the same object, magnetic stations have been successively established at Moscow, Barnaoul, the astronomical position of which I find to be at the foot of Altai, in lat. 53° 19′ 21″, long. 5h 27′ 20″ east of Paris, and at Nertschinsk.

The Academy of St.

Petersburgh has done still more, and has sent a courageous and clever astronomer, M. George Fuss, the brother of its perpetual secretary, to Pekin, and has procured the erection there of a magnetic pavilion, in the convent garden of the monks of the Greek church.

This undertaking cannot be mentioned without recalling the fact, that, according to the Penthsaoyani, a medical natural history composed under the Soung dynasty, nearly four hundred years before Christopher Columbus and the natives of Europe had the least idea of magnetic declination, the Chinese suspended the needle by means of a thread, to allow it perfect freedom of motion; and that they knew that when thus suspended, according to the method of Coulomb, (as in the Jesuit Lana’s apparatus in the seventeenth century,) the needle declined to the south-east, and never rested at the true south point.

Since the return of M. Fuss, M. Kowanko, a young officer of mines, whom I had the pleasure to meet in the Oural, continues the observations of horary declination, corresponding to those of Germany, St. Petersburgh, Cazan, and Nicolajeff in the Crimea, where Admiral Greigh has established one of Gambey’s compasses, the care of which is confided to the director of the Observatory, Mr. Knorre. I have also obtained the establishment of a magnetic apparatus at the depth of thirty-five fathoms in an adit in the mines of Freiberg in Saxony, where Mr.

Reich to whom we are indebted for his valuable labours upon the mean temperature of the earth at different depths, is assiduously engaged in making observations at regulated intervals. M. Boussingault, who neglects nothing which is calculated to advance the progress of the physics of the earth, has sent us from South America observations of horary declination made at Marmato, in the province of Antioquia, in north lat. 5° 27′, in a place where the declination is eastern, as at Cazan and Barnaoul in Asia; while on the north-western coasts of the new continent, at Sitka in the Russian settlements, Baron von Wrangel, also provided with one of Gambey’s compasses, has taken part in the simultaneous observations made at the time of the solstices and equinoxes.

A Spanish admiral, M. de Laborde, having been informed of a request that I had made to the Patriotic Society of the Havannah, had the kindness, unsolicited, to desire me to send him instruments proper for determining with precision the inclination, the absolute declination, and the horary variation of declination and intensity of the magnetic forces.

The valuable instruments desired, exactly similar to those in the possession of the Observatory of Paris, arrived in safety in the island of Cuba; but the alteration in the maritime command at the Havannah, and other local circumstances, have hitherto prevented the employment of them, and the establishment of a magnetic station under the tropic of Cancer.

The same has also occurred up to the present time with regard to one of Gambey’s compasses which M. Arago had caused to be erected, at his own expense, to obtain observations in the interior of Mexico, where the soil is elevated six thousand feet above the level of the sea.

Lastly, during my last residence in Paris, I had the honour of proposing to Admiral Duperré, Minister for marine affairs, the establishment of a magnetic station in Iceland.

The proposal was received with the utmost eagerness, and the instrument, which is already ordered, will be deposited during the present summer at the port of Reikiawig, when the expedition which has been sent to the north in search of M. de Blosseville and his companions in misfortune returns to Iceland to continue its scientific labours.

There cannot be any doubt that the Danish Government, which protects with generous ardour astronomy and the advancement of nautical science, will favour the establishment of a magnetic station in one of its provinces bordering on the polar circle.

At Chili also M.

Gay has made a great number of corresponding horary observations, according to the instructions of M. Arago.

I have entered upon this long and minute historical detail, to show how far I have hitherto succeeded, in conjunction with my friends, in extending the number of simultaneous observations.

After my return from Siberia, Mr. Dove and I published, in 1830, a graphic delineation of the curves of horary declination of Berlin, Freiberg, Petersburgh, and Nicolajeff in the Crimea, to show the parallelism of these lines, notwithstanding the distance of the stations and the influence of extraordinary perturbations.

In the comparison of the observations of St. Petersburgh and Nicolajeff, use has been made of observations taken at the very small intervals of twenty minutes.

It must not, however, be imagined that this parallelism of inflections always exists in the horary curves.

We have found that even in places very near to each other,—for instance, at Berlin and in the mines of Freiberg,—the magnetic reactions from the interior to the surface of the earth are not always simultaneous; that one of the needles presents considerable perturbations, while the other preserves that regularity, which under each meridian is the function of the true time of the place.

In the memoir published in 1830, I proposed the following periods for simultaneous observations at all the stations.

March 20th and 21st.

May 4th and 5th.

June 21st and 22nd.

Aug. 6th and 7th.

Sept. 23rd and 24th.

Nov. 5th and 6th.

Dec. 21st and 22nd.

From four o’clock in the morning of the first day, to midnight of the second day.

The observations to be continued at each magnetic station during the day and night, at intervals not exceeding one hour.

As several observers situated upon the line of the stations have found these periods too near to each other, it has been thought advisable to insist in preference upon the time of the solstices and equinoxes.

England, from the time of William Gilbert, Graham, and Halley to that of the more recent exertions of Messrs. Gilpin, Beaufoy (at Bushy), Barlow, and Christie, has produced a rich collection of materials applicable to the discovery of the physical laws which regulate the variation of the magnetic declination, either in one place according to the different hours and seasons, or at various distances from the magnetic equator and the lines without declination.

Mr. Gilpin made observations during twelve hours every day for more than seven months.

The numerous observations of Colonel Beaufoy were regularly published in Thomson’s Annals.

The memorable expeditions to the most inhospitable regions of the North have furnished Messrs. Sabine, Franklin, Hood, Parry, Henry Foster, Beechey, and James Clarke Ross with a rich harvest of important observations.

Physical geography is indebted for a considerable increase of knowledge respecting terrestrial magnetism and meteorology to the attempts which have recently been made to determine the form of the north-west passage or strait; and to the perilous explorations of the frozen coasts of Asia by Captains Wrangel, Lütke, and Anjou.

During the progress of these noble efforts, an unexpected impulse has been given to the physical sciences by the light thrown upon them by a branch of natural philosophy the theoretical progress of which for two centuries had been extremely slow.

Such has been the effect of the grand discoveries of Oersted, Arago, Ampère, Seebeck, and Faraday upon the nature of electro-magnetic forces.

Excited by the talents and ingenious exertions of learned travellers cooperating for the promotion of one object, Messrs. Hansteen, Due, and Adolphus Erman, by the fortunate union of very precise astronomical and physical means, have explored, throughout the immense extent of Northern Asia, the isoclinal, isogonal, and isodynamic curves for very nearly the same epoch.

When speaking of this great project, long since conceived and proposed by Mr. Hansteen, I ought, perhaps, to pass over in silence the observations upon magnetic inclination which I made upon the rarely-visited frontier of Chinese Dzoungarie and on the coasts of the Caspian Sea, published in the second volume of my Fragmens Asiatiques.

My learned countryman Mr.

Adolphus Erman, who embarked at Kamtschatka and returned to Europe by Cape Horn, had the rare advantage of continuing throughout a long voyage the measure of the three manifestations of terrestrial magnetism at the surface of the globe. He employed the same instruments and the same methods which he had made use of from Berlin to the mouth of the Oby, and thence to the Sea of Okhotsk.

That which characterizes our epoch, at a time distinguished by grand discoveries in optics, electricity, and magnetism, is the possibility of connecting phænomena by the generalization of empirical laws, and the mutual aid afforded by sciences which had long remained isolated.

At the present day simple observations upon horary declination or magnetic intensity, made simultaneously in situations very distant from each other, reveal, so to speak, what passes at profound depths in the interior of our planet, and in the superior regions of the atmosphere.

The luminous emanations, the polar explosions which accompany the magnetic storm, appear to follow great changes in the habitual or mean tension of terrestrial magnetism.

It would tend greatly to promote the advancement of the mathematical and physical sciences if, under the Presidency and auspices of Your Royal Highness, the Royal Society of London, to which I make it my boast to have belonged for twenty years, would exert its powerful influence to extend the line of simultaneous observations, and to establish permanent magnetic stations, either in the region of the tropics, on each side of the magnetic equator, the proximity of which necessarily diminishes the amplitude of the horary declinations, or in the high latitudes of the southern hemisphere and in Canada. I venture to propose this latter point, because observations upon horary declination made in the vast extent of the United States are still very rare.

Those, however, of Salem, in 1810, calculated by Mr. Bowditch, and compared by Arago with the observations of Cassini, Gilpin, and Beaufoy, merit great praise, and might serve as a guide to observers in Canada in investigating whether the declination there does not diminish between the vernal equinox and the summer solstice, contrary to what occurs in Western Europe.

In a memoir that I published five years ago, I suggested as magnetic stations extremely favourable to the progress of our knowledge, New Holland, Ceylon, the Mauritius, the Cape of Good Hope (rendered illustrious by the labours of Sir John Herschel), St. Helena, and some point on the eastern coast of America to the south of Quebec.

In the last century, in the years 1794 and 1796, an English traveller, Mr. Macdonald, made some new and important observations upon the diurnal motion of the needle at Sumatra and St. Helena, which have since been confirmed and extended upon a large scale in the scientific expeditions of Captains Freycinet and Duperrey; the former having the command of the sloop Uranie from 1817 to 1820, and the latter, who has six times crossed the magnetic equator, commanding the sloop Coquille from 1822 to 1825. To promote the rapid advancement of the theory of terrestrial magnetism, or at least to establish with more precision empirical laws, it is necessary at the same time to prolong and to vary the lines of corresponding observations; also to distinguish in observations of horary variations, what arises from the influence of the seasons, of serene and cloudy weather and of abundant rains, of the hours of day and night, and of the true time at each place, that is, from the influence of the sun, and of all isochronous influences at the different meridians.

To these observations of horary declination must be united those of the annual movement of the absolute declination, of the inclination of the needle, and of the intensity of the magnetic forces, the increase of which from the magnetic equator to the poles is unequal in the Western American and the Eastern Asiatic hemispheres.

All these data, indispensable bases for the future theory, can only acquire certainty and importance by the means of establishments which shall remain permanent for a great number of years, of Physical Observatories in which the investigation of numerical elements may be repeated at settled intervals of time, and with similar instruments.

Travellers who cross a country in but one direction and at one epoch merely prepare the way for an undertaking which should embrace the complete delineation of the lines without declination at intervals equally distant; the progressive removal of the points of intersection of the terrestrial and magnetic equators; the changes of form in the isogonal and isodynamic lines; and the influence upon the slow or accelerated movement of the curves, which indubitably arises from the configuration and articulation of the continents.

It must be considered fortunate if the isolated labours of travellers, whose cause it is my office to plead, have contributed to give animation to a species of investigation which is the work of centuries, and which requiries the concurrence of numerous observers, distributed according to a plan arranged after mature consideration, under the direction of several of the great scientific centres of Europe.

The directors should not always confine themselves to the narrow limits of the same instructions, but they should vary them freely in adaptation to the progressive state of physical science, and the improvement of instruments and methods of observation.

When soliciting Your Royal Highness to condescend to communicate this letter to the illustrious Society over which you preside, it is not in any degree my office to inquire, which are the magnetic stations that merit preference at the present time, or that local circumstances may admit of establishing.

To have solicited the concurrence of the Royal Society of London will be sufficient to give new life to a useful enterprise in which I have been engaged for very many years.

I venture simply to express the wish that, should my proposition be received with indulgence, the Royal Society would enter into direct communication with the Royal Society of Göttingen, the Royal Institute of France, and the Imperial Academy of Russia, in order to adopt measures the best adapted for the combination of what it may be proposed to establish with what already exists upon a very considerable extent of surface.

Perhaps also measures might be previously concerted for the publication of partial observations, and also (if the calculation would not require too much time, and too much retard the communications,) of the mean results.

One of the happy effects of civilization and the progress of reason is, that when addressing learned societies, their willing concurrence may be relied upon if the object for which it is solicited tends to promote the advancement of the sciences or the intellectual development of humanity.

Labours of astonishing precision have been performed, within the last few years, with instruments of extraordinary power, in a magnetic pavilion of the Observatory of Göttingen, which are well worthy of the attention of philosophers, as they offer a more precise method of measuring the horary variations.

The magnetized bar is of much larger dimensions than even the bar of Prony’s magnetic telescope; and the extremity is furnished with a mirror, in which are reflected the divisions of a scale which is more or less distant, according to the angular value desired to be given to these divisions.

By the employment of this improved method the necessity for the observer’s approaching the magnetized bar is obviated, and by preventing the currents of air produced by the proximity of the human body, or during the night, of a lamp, observations may be made in the smallest intervals of time.

The great geometrician Mr. Gauss,—to whom we owe this mode of making observations, as well as the means of reducing the intensity of the magnetic force in any part of the earth to an absolute proportion, and the ingenious invention of a magnetometer put into motion by a multiplier of induction,—published in the years 1834 and 1835 several series of simultaneous observations made with similar apparatus, and at intervals of five or ten minutes, at Göttingen, Copenhagen, Altona, Brunswick, Leipzig, Berlin (where Mr.

Encke has already established a very spacious magnetic house, near the New Royal Observatory), Milan, and Rome. Mr. Schumacher’s German Ephemeris (Jahrbuch für 1836) proves graphically, and by the parallelism of the smallest inflections of the horary curves, the simultaneity of the perturbations at Milan and Copenhagen, two cities having a difference of latitude of 10° 13′.

Mr. Gauss first made observations at the times which I proposed in 1830, but with the intention of referring the angular dimensions of magnetic declination to the smallest intervals of time.

(On the 7th of February 1834, alterations of six minutes of the arc corresponded to a single minute of time.)

Mr. Gauss reduced the forty-four hours of simultaneous observations to twenty-four hours; and appointed six [seven?] periods of the year, viz. the last Saturday of each month consisting of an uneven number of days, for the stations which are provided with his new apparatus.

The small magnetized bars which he employs as magnetometers are of four pounds weight, and the large ones of twenty-five pounds.

The curious apparatus of induction proper to render sensible and measurable the oscillatory movements predicted by a theory founded upon Mr. Faraday’s admirable discovery, consists of two bars fastened together, each of twenty-five pounds weight.

I thought it proper to mention the valuable labours of Mr. Gauss, in order that those members of the Royal Society of London who have rendered most service to the study of terrestrial magnetism, and who know the localities of the colonial establishments, may take into consideration whether bars of great weight, provided with a mirror, and suspended in a pavilion carefully closed, should be employed in the new stations to be established; or whether Gambey’s compass, hitherto uniformly used in our present stations in Europe and Asia, should still be employed.

In discussing this question the advantages will undoubtedly be estimated which, in the apparatus of Mr. Gauss, arise from the smaller mobility of the bars by currents of air, as well as from the facility and rapidity with which the angular divisions may be read in very short intervals of time.

My desire is only to see the line of magnetic stations extended, whatever be the means by which the precision of the corresponding observations may be attained. I ought also to mention that two accomplished travellers, Messrs. Sartorius and Listing, provided with very portable instruments of small dimensions, have very successfully employed the method of the great geometrician of Göttingen in their excursions to Naples and in Sicily.

An abstract of a memoir by Prof.

Gauss in which his apparatus and method of observation are fully described will be found in Lond. & Edinb. Phil. Mag., vol. ii. p. 291, et seq.—Edit.

Your Royal Highness will, I hope, excuse the length of this communication; but I thought that it would be useful to unite under one point of view what has been done or proposed in different countries towards the attainment of extensive simultaneous observations upon the laws of terrestrial magnetism.

Accept, Sir, the acknowledgement of the profound respect with which I have the honour of being, Your Royal Highness’s, &c. &c., Berlin, April, 1836.

Alexander von Humboldt.