Page images
[ocr errors]

firmed by Sabine and the French physicists in Lapland in 1838.21

While in this careful development of the present condition of our positive knowledge of the phenomena of terrestrial magnetism, I have necessarily limited myself to a mere objective representation of that which did not even admit of being elucidated by merely theoretical views, based only upon induction and analogy ; I have likewise purposely abstained in the present work from entering into any of those geognostic hypotheses, in which the direction of extensive mountain chains and of stratified mountain masses is considered in relation to its dependence upon the direction of magnetic lines, more especially the isoclinal and isodynamic systems. I am far from denying the influence of all cosmical primary forces-dynamic and chemical forces--as well as of magnetic and electrical currents on the formation of crystalline rocks and the filling up of veins ;22 but owing to the progressive movement of all magnetic lines and their consequent change of form, their present position can teach us nothing in reference to the direction in primeval ages of mountain chains, which have been upheaved at very

different epochs, or to the consolidation of the earth's crust, from which heat was being radiated during the process of its hardening.

Of a different order, not referring generally to terrestrial magnetism, but merely to very partial local relations, are those geognostic phenomena, which have been designated by the name of the magnetism 23 of mountain masses. These phenomena engaged much of my attention before my American expedition, at a time when I was occupied in examining the magnetic serpentine rock of the Haidberg mountain in Franconia in 1796, and then gave occasion in 21 Sabine, On Days of Unusual Magn. Disturbances, pt. i, p. xviii

. M. Bravais concludes from the observations made in Lapland that the horizontal intensity diminishes when the phenomenon of the Aurora borealis is at its maximum" (Martins, p. 461).

22 Delesse, Sur l'association des minéraux dans les roches qui ont un pouvoir magnétique élevé, in the Comptes rendus de l'Acad. des Sc. t. xxxi, 1850, p. 806; and Annales des Mines, 4ème Série, t. xv (1849),

Reich, Ueber Gebirgs- und Gesteins-Magnetismus, in Poggend. Ann. Bd. lxvii, s. 35.

p. 130.


Germany to a considerable amount of literary dissension, which, however, was of a very harmless nature. They present a number of problems, which are by no means incapable of solution, but which have been much neglected in recent times, and only very imperfectly investigated both as regards observation and experiment. The force of this magnetism of rocks


be tested for the determination of the increase of magnetic intensity by means of pendulum experiments and by the deflection of the needle in broken off fragments of hornblende and chloritic schists, serpentine, syenite, dolerite, basalt, melaphyre and trachyte. We may in this manner decide by a comparison of the specific gravity, by the rinsing of finely pulverised masses, and by the application of the microscope, whether the intensity of the polarity may not depend in various ways upon the relative position, rather than upon the quantity, of the granules of magnetic iron and protoxide of iron, intermixed in the mass. More important, however, in a cosmical point of view is the question which I long since suggested in reference to the Haidberg mountain ; whether there exist entire mountain ranges, in which opposite polarities are found to occur on opposite declivities of the mass.24 An accurate astronomical determi

24 This question was made the subject of lively discussion when, in the year 1796, at the time that I fulfilled the duties of superintendent of the mining operations in the Fichtelgebirge, in Franconia, I discovered the remarkable magnetic serpentine mountain (the Haidberg) near Gefress, which had the property at some points of causing the needle to be deflected at a distance of even 23 feet (Intelligenz-Blatt der Allgem. Jenaer Litteratur-Zeitung, Dec. 1796, No. 169, s. 1447, and März, 1797, No. 38, s. 323 — 326; Gren's Neues Journal der Physik, Ed. iv, 1707, s. 136; Annales de Chimie, t. xxii, p. 47). I had thought that the magnetic axes of the mountain were diametrically opposed to the terrestrial poles ; but according to the investigations of Bischoff and Goldfuss, in 1816 (Beschreibung des Fichtelgebirges, Bd. i, s. 176), it would appear that they discovered magnetic poles, which penetrated through the Haidberg and presented opposite poles on the opposite declivities of the mountain, while the directions of the axes were not the same as I had given them. The Haidberg consists of dull green serpentine, which partially merges into chloritic and hornblende schists. At the village of Voysaco, in the chain of the Andes of Pasto, we saw the needle deflected by fragments of porphyritic clay, while on the ascent to Chimborazo, groups of columnar masses of trachyte disturbed the motion of the needle at a distance of three feet. It struck me as a very remarkable fact that I should have found in the black and red nation of the position of such magnetic axes of a mountain would be of the greatest interest, if it could be ascertained obsidians of Quinche, north of Quito, as well as in the gray obsidian of the Cerro de la Navajas of Mexico, large fragments with distinct poles. The large collective magnetic mountains in the Ural chain, as Blagodat, near Kuschwa, Wyssokaja Gora, at Nishne Tagilsk, and Katschkanar, near Nishne Turinsk, have all broken forth from augitic or rather uralitic porphyry. In the great magnetic mountain of Blagodat, which I investigated with Gustav Rose, in our Siberian expedition, in 1829, the combined effect of the polarity of the individual parts did not indeed appear to have produced any determined and recognisable magnetic axes. In close vicinity to one another lie irregularly mixed opposite poles. A similar observation had previously been made by Erman (Reise um die Erde, Bd. i, s. 362). On the degree of intensity of the polar force in serpentine, basaltic, and trachytic rock, compared with the quantity of magnetic iron and protoxide of iron, intermixed with these rocks, as well as on the influence of the contact of the air in developing polarity, which had already been maintained by Gmelin and Gibbs, see the numerous and very admirable experiments of Zaddach, in his Beobachtungen über die Magnetische Polarität des Basaltes und der Trachytischen Gesteine, 1851, 8. 56, 65—78, 95. A comparison of many basaltic quarties, made with a view of ascertaining the polarity of individual columns which have stood isolated for a long period, and an examination of the sides of these columns wbich have been recently brought in contact with the outer air in consequence of the removal from individual masses of a certain depth of earth, have led Dr. Zaddach to hazard the conjecture (see s. 74, 80) that the polar property, which always appears to be manifested with the greatest intensity in rocks to which the air has been freely admitted, and which are intersected by open fissures, " diffuses itself from without inwards, and generally from above downwards.” Gmelin expresses himself as follows in respect to the great magnetic mountain, Ulu-utasse-Tau, in the country of the Baschkiri, near the Jaik :-“The sides which are exposed to the open air exhibit the most intense magnetic force, while those which lie under ground are much weaker" (Reise durch Siberien, 1740—1743, Bd. iv, s. 345). My distinguished teacher, Werner, in describing the magnetic iron of Sweden, in his lectures, also spoke of “the influence which contact with the atmo. sphere might have, although not by means of an increased oxidation, in rendering the polar and attracting force more intense.” It is asserted by Colonel Gibbs, in reference to the magnetic iron mines at Succassuny, in New Jersey, that "the ore raised from the bottom of the mino has no magnetism at first, but acquires it after it has been some time exposed to the influence of the atmosphere" (On the connexion of Magnetism and Light, in Silliman's American Journal of Science, vol. I, 1819, p. 89). Such an assertion as this ought assuredly to stimulate observers to make careful and exact investigations! When I drew attention in the text (see page 160), to the fact that it was not only the quantity of the small particles of iron which were intermixed in the stone, but also their relative distribution (their position) which acted as the reVOL. V.


after considerable periods of time, that the three variable elements of the total force of terrestrial magnetism caused either an alteration in the direction of the axes, or that such small systems of magnetic forces were at least apparently independent of these influences.


[ocr errors]

Reaction of the interior of the Earth upon its surface ; manifesting itself :-a. Merely dynamically, by tremulous undulations (earthquakes) ;—b. By the high temperature of mineral springs, and by the difference of the intermixed salts and gases (Thermal springs); c. By the outbreak of elastic fluids, sometimes accompanied by phenomena of spontaneous ignition (gas and mud volcanoes, burning naphtha springs, Salses); d. By the grand and mighty actions of true volcanoes, which (when they have a permanent connexion with the atmosphere by fissures and craters) throw up fused earth from the depths of the interior, partly only in the form of red-hot cinders, but partly submitted to varying processes of crystalline rock formation, poured out in long, narrow streams.

In order to maintain, in accordance with the fundamental plan of this work, the co-ordination of telluric phenomena sultant upon the intensity of the polar force, I considered the small particles to be so many small magnets. See the new views regarding this subject in a treatise by Melloni, read by that distinguished physicist before the Royal Academy at Naples, in the month of January, 1853 (Esperienze intorno al Magnetismo delle Rocche, Mem. i, Sulla Polarità). The popular notion which has been so long current, more especially on the shores of the Mediterranean, that if a magnetic rod be rubbed with an onion, or brought in contact with the emanations of the plant, the directive force will be diminished, while a compass thus treated would mislead the steersman, is mentioned in Procli Diadochi Paraphrasis Ptolem. libri iv, de Siderum affectionibus, 1635, p. 20 (Delambre, Hist

. de l'Astronomie Ancienne, t. ii, p. 545). It is difficult to conceive what could have given occasion to so singular a popular error.


-the co-operation of a single system of impelling forces in the descriptive representation, we must here remind the reader, how, starting from the general pr perties of matter, and the three principal directions of its accivity (attraction, vibrations producing light and heat, and electro-magnetic processes), we have in the first section taken into consideration the size, form, and density of our planet, its internal diffusion of heat and of magnetism, in their effects of intensity, dip, and variation, changing in accordance with definite laws. The directions of the activity of matter just mentioned are nearly allied' manifestations of one and the same primitive force. They occur in a condition of the greatest independence of all differences of matter, in gravitation and molecular attraction. We have at the same time represented our planet in its cosmical relation to the central body of its system ; because the internal primitive heat, which is probably produced by the condensation of a rotating nebular ring, is modified by the action of the sun (Insolation). With the

same view, the periodical action of the solar spots (that is to say, the frequency or rarity of the apertures in the solar envelopes) upon terrestrial magnetism, has been referred to, in accordance with the most recent hypotheses.

The second section of this volume is devoted to the entirety of those telluric phenomena which are to be ascribed to the constantly active reaction of the interior of the earth upon its surface. To this entirety I give the general name of Vulcanism or Vulcanicity; and I regard it as advantageous to avoid the separation of that which is causally connected and differs only in the strength of the manifestation of force and the complication of physical processes. By taking this general view, small and apparently unimportant phenomena acquire a greater significance. The unscientific observer who comes for the first time upon the basin of a thermal spring and sees gases capable of extinguishing light rising in it, or who wanders amongst rows of changeable cones of mud volcanoes, scarcely exceeding himself in height, never dreams that in the calm space occupied by the latter, eruptions of fire to the he yht of many thousand feet have often taken place; and that one

1 Cosmos, vol. iii, p. 39.
L'osmos, vol. i, p. 197—199.


« PreviousContinue »