Abbildungen der Seite
PDF
EPUB

tween them; that they show how far Kasan therefore periodic, and capable of being lies eastwards from Göttingen or the banks of represented empirically in functions of the the Seine. There are also places on the globe the time-the elements returning to their where the navigator, surrounded by fogs for

many days, without sun or stars, and without any means of determining the time, can tell with certainty from the magnetic dip whether he is placed north or south from the haven of which he is in search.'-Kosmos, p. 185.

original values, after the lapse of a year and of a day respectively. They are also disturbed in an irregular and capricious manner, as we have already mentioned, and to these disturbances we shall immediately return.

This last application of magnetic science In Humboldt's notes the reader will find to navigation was, as Humboldt tells us some curious information on this part of (Kosmos, p. 429), proposed by our most the subject. The total intensity of the ingenious countryman, Gilbert, soon after magnetic forces was studied much later the invention of the dipping-needle by Nor- than the others, and up to a recent period man, towards the end of the 16th century. no kind of approximation had been made It is particularly applicable, says Humboldt, to the isodynamic lines. Humboldt conto the navigation of the west coast of Southsiders his ascertainment of the gradual deAmerica. It must be added, however, crease of intensity from the temperate zone that the determination of longitudes, wide- to the equator as the most important result ly apart, by means of magnetic perturba- of his great journey to the Tropics (Kosmos, tions, seems a doubtful application, since p. 434). We appreciate, therefore, the the publication by Colonel Sabine of the magnanimity with which (note 29, p. 432, comparative curves of disturbances at To- &c.) he discusses the claims of his prederonto and at Prague, which do not present cessors to this discovery. Humboldt anthe strict accordance noticed in the Euro-nounced his conclusion to the Paris Acadpean observations. emy of Sciences on the 26th Frimaire, Terrestial magnetism, its recent history, An XIII. (17th December, 1804), which and the especial interest which attaches established the universally received value to it at the present moment, from the of the magnetic intensity at Paris = 13482; unexampled labors in different parts of that at the magnetic equator in Peru being the globe, patronized by the Russian and 1.0000. Admiral de Rossel's result, English governments and by the East In- though founded on observations made in dia Company, in order to advance it speed- 1791-4, was only published in 1808; and ily and effectually, have been fully explain- consequently it is uncertain whether their ed in an article in the Quarterly Review author was aware of their exact import for 1840. We may therefore pass rapidly sooner, since he had certainly not commuover one of the most attractive subjects nicated it to his friends. But Humboldt which the enlarged science of physical ge- has found, from an unpublished letter of ography presents. It will be sufficient to Lamanon, that this important fact had been remind the reader that the science of ter- already expressly deduced, in 1787, from restrial magnetism (empirically considered) the observations made during Laperouse's involves three elements,-variation (or de- voyage. The scientific world will have clination), dip (or inclination), and inten- little difficulty in leaving Humboldt in possity; and that the simultaneous condition session of the reputation which his discovof these three elements may be expressed ery has given him, since, though (like by the ingeniously compendious notation of curved lines, drawn upon a terrestrial map-passing through all the points which have the same magnetic variation, for example-and so likewise for the other two elements. It is impossible to estimate too highly the value of such graphical methods; at first only technical memories, they become engines of the most subtle discoveries. These elements vary. They vary from age to age, so that the magnetic charts do not remain exact for any considerable space of time. They have also annual and diurnal changes, which are

most other great facts in science) only a rediscovery of something already known or guessed at, he first saw its importance, and published it to the world, accompanied by sufficient evidence.

There is a long and very interesting note (36, p. 436) which gives a detail, highly creditable to Baron Humboldt, of the share which his eminently practical mind has had in forwarding the science of magnetism, and in aiding, and indeed originating, the impulse which that part of physics has received in our own day. From this note it appears that, after his return from Ameri

ca, whilst residing in Berlin, in 1807-8, he the similarity and simultaneity of the discommenced a series of closely consecutive turbances were fully proved by graphical magnetic observations, pursued day and projections, which were published in Pognight for several days, at the period of the gendorff's Annals. But this was only a solstices and equinoxes, in which he was commencement; for the following year aided by his friend Oltmanns. These ob (129) having undertaken, by desire of the servations, which probably were originally Emperor of Russia, a scientific journey to intended to ascertain the regular diurnal Siberia, he took occasion to recommend to periods whose existence had been known the Emperor the establishment of a chain for the greater part of a century, led to the of magnetic stations in his vast dominions. discovery of recurring but irregular pertur- The Academy of Sciences, and Corps of bations-called by him magnetic storms- Mines, obedient to the Imperial decree, which he immediately perceived the im- instituted at Humboldt's suggestion the portance of studying with reference to system of observation which has since been their simultaneity in different parts of the continued and improved. earth's surface. But circumstances pre- Our author next speaks in most becoming vented his following them out. His change terms of his acute countryman Gauss, of residence to Paris, and the political con- who soon after (1832) taking up the subvulsions of the time, were amongst these; ject both mathematically and practically, and here we are again reminded, in our increased as much the delicacy of the perusal of Humboldt's Personal History, methods of observation as the value and of the inestimable benefits to science of the definiteness of the observations themprofound peace which we at present enjoy. selves, considered as the elements of a Oersted's great discovery of the connexion physical theory. But when the test of this of electricity and magnetism awakened in theory was involved in the institution of 1820 fresh attention to the subject: and we physical observations at many points, as presume it was by Humboldt's advice and remote as possible from one another, over influence that his friend Arago's valuable the globe, Humboldt's influence aud Hum(but hitherto unfortunately unpublished); bold's savoir were again called into requimagnetic observations at Paris were com- sition. Casting his eyes over the political pared with simultaneous observations at divisions of the earth, he saw that if EngKasan in Russia, when the similarity of the land and Russia combined their influence, perturbations and the influence of the Au- the problem would be solved. In 1836 he rora Borealis were clearly perceived.* wrote to the Duke of Sussex, as President On Humboldt's return to Berlin, in 1828, of the Royal Society, desiring his and he recommenced his own long-interrupted their influence with the British governlabor, with the advantage of simultaneous comparable observations at Paris and in the depths of the Saxon mines; and then

ment to have magnetic observations established at points of our colonial possessions, which he had already five years before (therefore previous to Gauss's publication), Not, however, discovered for the first time. indicated as important for the ends of sciThe simultaneity at distant points had already ence; namely, Canada, St. Helena, the been ascertained by Celsius and Graham, in 1741, Cape of Good Hope, the Isle of France, whilst residing the one at Upsala and the other in London. The magnetic influence of the Aurora, Ceylon, and New Holland. These requiwhich Humboldt (p. 199) attributes exclusively sitions have been, for the national honor to Arago (wie Arago zuerst entdekt hat), was of Britain, almost literally carried out; and clearly established by the Swedish observers, Cel- though the results are yet very imperfectly sius, Hiorter, and Wargentin, between 1740 and 1750, in a number of special cases, the details of known, and cannot now be further alluded which are recorded. These being detailed in to, Humboldt must derive imperishable Kämtz's Meteorologie (iii 494, &c.), in the very faine from having originated and impelled part of that work cited in the Kosmos (p. 442), the movement, which was in his own counpass them over in favor of the French Academi- try so powerfully stimulated by the sagaciIf he justifies it on the ground of the ob- ty of Gauss, and so generously acted on in servations being made at so great a distance from ours by Herschel, Sabine, Airy, Lloyd, and the Arctic Circle as Paris, he should recollect an Brisbane. observation of his own made in 1806, and demonstrating the same fact (Gilbert's A nalen, xxix 425, quoted by K-mtz). We find in all this a disagreeable tampering (even at a personal sacrifice) with the integrity of scientific history.

we do not think that our author was entitled to

cian.

In page 428, Note 13, at the end, Humboldt, speaking of observations of Magnetic Storms,' uses these expressions :—

'One of the most remarkable disturbances

was that of the 25th of September, 1841, intellectual, should be concentrated from which was observed at Toronto in Canada, at minute to minute and from hour to hour the Cape of Good Hope, at Prague, and par- (so long as the wants of nature could tially in Van Diemen's Land. The English be postponed), on the incessant watching festival of Sunday, upon which it is sinful

(sündhaft) after midnight on Saturday to read of three vibrating bars.

To those who off a scale or to follow out in all their devel- understand what such tasks imply, we opment great natural phenomena, put a stop need say nothing of this becoming Sunto the observation, since, on account of the dif- day's employment; but we may mention, ference of longitude of Van Diemen's Land, for the information of others, that one of the magnetic storm happened there upon a Gauss's most zealous pupils had almost Sunday!' sacrificed his life, through the consequences of a brain fever caught under the burning climate of Sicily, solely from pursuing the Sunday's relaxations of Göttingen. We repeat, that such a positive institution of Sunday term-days was disgraceful. to Christendom, and it was so felt by the English philosophers, who refused to join the German confederation of magnetists in carrying out their system of observation. The confederation was therefore fain to indulge the English scrupulosity, and hence no doubt the sally in the Kosmos. When Mr. Airy (our excellent Astronomer Royal) mentioned these circumstances at the most crowded meeting which took place in the Senate-house at Cambridge, during the late visit of the British Association, the unanimous opinion of the assembly was suffi ciently marked.

We are surprised that Baron Humboldt, usually so cautious in imputing blame, should have thus attempted to cast ridicule upon the English government and English men of science, and upon such a ground. But the statement having been made in ignorance of how these things are really managed with us, it requires a word of explanation. It is quite certain that the English philosophers declined to accede to the Göttingen terms,' or fixed days of continued observation from five minutes to five minutes for twenty-four hours or more, which had been fixed, in defiance of the immemorial usage of all Christian communities, UPON SUNDAYS,' for general convenience' (of the Jews we suppose). Here is no question of whether the mode of keeping the Sabbath in Scotland or at Geneva, But if Baron Humboldt had lived longin England or at Rome, be most correct; er in England, or had even questioned any it is no question of whether amusements one competent English authority, he would are to be indulged in or not; whether or have known that it would not be considernot the theatres should be shut; it is the ed as sinful' by, we suppose, any sciensimple question whether the seventh day is tific man in this island to read off a scale to receive any distinctive observance what-after the clock had struck twelve on Sat, ever-whether the hebdomadal division of urday night, in order to observe an extratime, which even Laplace traced in its ori- ordinary natural phenomenon. Here is an gin to the very dawn of civilization, is to example in point. In 1836 an annular be annihilated. Is there, we would ask, eclipse of the sun was visible in the northan observatory in Europe which has not ern part of this kingdom (where the obserits congés de Dimanche? In any country vance of Sunday is supposed to be more where we ever spent a Sunday it was claimed strict than elsewhere) during church-time even by those who wholly neglected its re- on Sunday, the 15th of May. What was ligious duties, by a prescriptive and inde- the consequence? The service was postfeasible right as a day of unbending, of poned, and the whole population saw the relaxation, and of social converse. We phenomenon, astronomers inclusive. The need but mention a single instance, be- usage at Greenwich Observatory we believe cause it expresses the extreme case of to be this: the whole staff are at liberty compliance with a usage handed down on Sunday, except when an observation is from the remotest generations: we mean to be made of no great continuance, and the practice of the Polytechnic school of which is likely to be of value to the inteParis, where Sunday is kept holiday.' rests of astronomy, or for the special imBut our German friends emancipated them- provement of the lunar tables;—any exselves even from these relics of an ancient traordinary or unique phenomenon would superstition, and declared that the first day be observed as a matter of course-but of the week should be the hardest day of computations and all other work which can all; when the whole energies, physical and be done during the rest of the week are VOL. VII.-No. III. 24

[ocr errors]

entirely suspended. Being ourselves fully observed for one that is missed. As to inclined to regard the usages of different mean results, the omission of the seventh countries and sects with charity, and, in- day is inappreciable; and if it be said deed, to admit that no absolute standard of that magnetic disturbances come under conduct can be named on this subject suit- the class of extraordinary and unique pheable to all nations and all times, we are surprised that a cosmopolite traveller and grave sage should have on this occasion permitted himself the double indulgence of a blunder and a sneer.

nomena, before which the repose of Sunday gives way as matter of common sense, we must observe that these disturbances can only be seen by watching for them ; they do not yet (whatever art may one day There is that, however, in the case be- achieve) announce themselves. To note fore us which requires it to be judged by a disturbances at all on Sundays requires the more specific rule than that of national mo- usual observations to be made as a matter rality or individual opinion. The system of course; and where the system of obserof magnetic observatories in the colonies vation extends round the globe, to have uniis a military one, conducted solely by mili-versally simultaneous comparisons could tary men, officers and non-commissioned not be effected otherwise. After all, we do not suppose that if the officers of the Royal Artillery. In every department of the public service complicated officer in command at Van Diemen's Land systems of duty must be conducted on fixed had been aware of the peculiar interest of and precise rules. As artillerymen, they the phenomenon, of which the observation were engaged to work six days in the was commenced on Saturday, he would week, not seven. No option could be left have been deterred either by conscientious to them to observe on Sundays or not as scruples or by the fear of disobeying orders, they pleased; it would have been an unfair from pursuing his inspection of the mag imputation of want of zeal upon any whose nets after the clock struck twelve. But we conscientious scruples or the limit of see one circumstance in the detail of the physical strength did not admit of their observation as published by the Board of complying. And the importance of this Ordnance, which leads to a different conrule of no work on Sundays is so great, jecture; the observation at midnight 'was that not to have adhered to it must have missed;' the last recorded was 11h. 45m. changed the whole system of observation. (local time). The facts seem to speak for For the personal strength of the observa- themselves; no doubt our non-commistories must have received a large accession sioned officer, worn out by many hours' in order to overtake the exhausting labor of watching, fell asleep, and perhaps was awaperpetually observing and computing. To kened to a sense of his position by the do a sixth part more work would have re- bright sun of a Sunday morning, pleasant quired, we are certain, a far more than pro- to him as a day civilly, at least, if not magportional increase of the staff, and besides netically, free from perturbations. must sooner or later bring upon the most conclude-we have carefully examined Sir zealous a sense of unremitting drudgery. James Ross's observations made at sea in A periodical absolute cessation of a kind of the late Antarctic expedition (Phil. Trans. work in its nature calculated to produce a 1843, 1844) with a view to this question. speedy satiety, is undoubtedly on mere hu- The result is such as we should have antiman principles a most wise legislative and cipated. Sir James's short stay in the pereconomical provision. We reply, then, to ilous seas of these high latitudes, whither those who wish the colonial observatories he was sent expressly for the accumulation to be worked seven days a-week, in the of magnetical observations, impelled him characteristic language of the French func- to use every favorable opportunity, whether tionary, 'It would be worse than a crime-on Sunday, or not, for making such obserit would be a blunder.' And where, after all, is the loss? Perhaps during the whole five years that the observations were intended to continue, a second great disturb ance might not occur on Sunday, and in any period of observation six such will be

* Colonel Sabine's Introduction to Observations at Toronto, 4to. 1845, p. 13.

Το

vations as, requiring but a short time, if postponed, must have been inevitably lost.

From Magnetism the Baron proceeds to the consideration of the Polar lights, which are so evidently connected with it. We wish we could afford space to transcribe his

Sabine on Observations of unusual Magnetic Disturbance, 4to, 1843, p. 87, col. 1.

excellent picture of auroral phenomena that some plants increase from the exterior (p. 199,) and his judicious remarks on their or by superposition of coats, whilst others connection with circumstances purely at- are constantly pushing their fresh supplies mospheric; we should have demurred, how- of material from within outwards. The ever, to his comparison between our Polar analogy (even supposing the botanical fact lights and the feeble phosphorescence (as admitted, which is not the case) is undoubtit has been called) of the unilluminated edly more apparent than real, and expresses parts of the moon and Venus; and we no more than the division of igneous and should also have questioned whether science sedimentary rocks, with which geologists is advanced by classifying under the com- have long been familiar. Without quarrelmon head of earthlight' such diverse facts ling with names, however, we find formaas the aurora, the supposed luminosity of tions divided according to their origin into certain fogs, the animal light of the ocean, four classes (p. 258). The first is the enand the dark light' of Moser's pictures dogenous, or, as it has been better termed (Kosmos, p. 206, &c.); but our diminishing by some English geologists, hypogene class. space warns us to be brief, and we pass on It includes, according to Humboldt-1, to the important class of facts more imme- granite and syenite, on which formations he diately connected with geology. gives some curious details, especially as to the extensive superposition of granite upon slates in the valley of the Irtysch in Siberia (p. 262); 2, quartz porphyry; 3, greenstone; 4, hypersthene; 5, euphotide and serpentine; 6, augitic rocks; 7, basalt and trachyte. The second class of rocks, which are, according to the author's view, exogenous, include sedimentary deposits of matter either dissolved or suspended in a fluid; such are-1, slates, up to the Devonian series; 2, coal-formation deposits; 3, the whole series of limestones-except 4, travertine or modern fresh-water deposits; 5, deposits formed of infusoria. The third class is composed of rocks, also sedimentary, but transformed in their physical and chemical characters by the superinduced action of the endogenous rocks of the first class. This introduces us to the wide and curious field of metamorphism, which the author illustrates by an interesting collection of examples and special cases, commencing with the effects of heat upon crystals and simple substances observed in the laboratory by Rose and Mitscherlich, and on natural and artificial compounds, variously cooled, by Sir James Hall and Gregory Watt (p. 271, 274, 457). Cases occurring in nature are next considered, such as the crystallization and formation of new cleavages in slates near their junction with igneous rocks, and the tendency to the development of segregated quartz in those formations (p. 272); the conversion of chalk and oolite into statuary marble, and of limestone into dolomite or into gypsum by the presence of certain intrusive rocks (pp. 272, 274, 278). The formation of quartz rock, and those in which garnet enters abundantly, is also considered as a metamorphic action. The doctrine of met

The doctrine of the heat of the earth led us in one direction to the magnetic and electric phenomena which appear to be intimately connected with it (as exemplified by the similarity of the isothermal and magnetic curves first noticed by Sir D. Brewster, and by the fact of diurnal and annual magnetic periods); but there is a very different class of effects probably also due to it-the production, namely, of hot-springs, earthquakes, and volcanoes, the elevation of continents, the rupture of strata, and the metamorphosis of rocks. This mode of presenting the connected sciences is not less elegant than just. The range of phenomena connected with volcanoes (which form as it were their middle term and most characteristic type) is startling, but cannot be denied to be ingenious. It commences with earthquakes, (p. 210,) emissions of gas, of water, i. e. cold and hot springs, pure or mineral; next, mud volcanoes, lavic volcanoes possessing craters, dome-shaped trachytic mountains, whose matter has been ejected, but not burst open into the crater form lastly, elevation craters, or mountains elevated and opened at top, but without emission of lavas. Of all this we should like to have given some account, but the reader of Humboldt's writings cannot expect much new on the subject of volcanoes. Teneriffe and Pichincha are already old friends; and for European volcanoes, and, we may add, for the whole theory, our author simply reproduces the well-known views of Von Buch.

In treating of geological formations, the Baron describes rocks as distinguished by their origin into two divisions, which he somewhat quaintly calls endogenous and exogenous, from the alleged fact in botany

« ZurückWeiter »