EARTHQUAKES. 



01 



have imagined as the substrate of the northern 1 

 lights. 



If the luminous phenomenon which we as- 

 cribe to a galvanic current, i. e. a motion of 

 electricity in a circuit returning into itself, be 

 designated by the indefinite name of the North- 

 ern light, or the Polar light, nothing more is 

 thereby implied than the local direction in 

 which the beginning of a certain luminous phe- 

 nomenon is most generally, but by no means 

 invariably, seen. What gives this phenomenon 

 its greatest importance is the fact which it re- 

 veals, viz. that the Earth is luminous ; that 

 our planet, beside the light which it receives 

 from the central body, the sun, shows itself 

 capable of a proper luminous act or process. 

 The intensity of the Earth-light, or rather the 

 degree of luminosity which it diffuses, exceeds 

 by a little, in the case of the brightest coloured 

 rays that shoot up to the zenith, the light of 

 the moon in her first quarter. Occasionally, as 

 on the 7th of January, 1831, a printed page can 

 be read without straining the sight. This light- 

 process of the earth, which the Polar regions 

 exhibit almost incessantly, leads us by analogy 

 to the remarkable phenomenon which the planet 

 Venus presents. The portion of this planet 

 which is not illuminated by the sun, glows oc- 

 casionally with a proper phosphorescent gleam. 

 It is not improbable that the Moon, Jupiter, and 

 Comets, besides the reflected sun-light recog- 

 nizable by the polariscope, also emit light pro- 

 duced by themselves. Without insisting on the 

 problematical but very common phenomenon 

 of sheet-lightning, in which the whole of a deep 

 massy cloud is flickeringly illuminatecf for sev- 

 eral minutes at a time, we find other examples 

 of terrestrial evolutions of light. To this head 

 belong the celebrated dry-fogs of 1783 and 1831, 

 which were luminous by night ; the steady lu- 

 minottsness of large clouds, perfectly free from 

 all flickering, observed by Rosier and Beccaria ; 

 and even the pale, diffused light, as Arago has 

 well observedfi*'), which serves to guide us in 

 the open air, in thickly clouded autumn and 

 wintry nights, when there is neither moon 

 nor star in the firmament, nor snow upon the 

 ground. As ia the phenomenon of the Polar 

 lights occurring in high northern latitudes, in 

 other words, in electro-magnetic storms, floods 

 of flickering and often parti-coloured light 

 stream through the air, so, in the hotter zones 

 of the earth, between the tropics, are there 

 many thousand square miles of ocean which 

 are similarly light-engendering. Here, how- 

 ever, the magic of the light belongs to the or- 

 ganic forces of nature. Light-foaming flashes 

 the bursting wave, the wide level glows with 

 lustrous sparks, and every spark is the vital 

 motion of an invisible animal world. So mani- 

 fold is the source of terrestrial light. And shall 

 we conceive it latent, not yet set free in va- 

 pours, as a means of explaining Moser's pic- 

 tures — a discovery in which reality still pre- 

 sents itself to us as a vision shrouded in mys- 

 tery 1 



As the internal heat of our planet is connect- 

 ed on one hand with the excitement of electro- 

 magnetic currents and the light-producing pro- 

 cess of the earth (a consequence of the burst- 

 ing of a magnetic storm), so on the other hand 



does it also manifest itself a« a principal source 

 of geognostic phenomena. These we shall con- 

 sider in their connection, and in their transition 

 from a merely dynamic concussion, and from 

 the upheaving of continents and mountain mass- 

 es, to the production and effusion of gases and 

 liquids, of boiling mud, and of red hot and molt- 

 en earths, which harden into crystalline rocks. 

 It is no trifling advance in the newer geognosy 

 (the mineralogical portion of the physics of the 

 globe), that it has firmly founded the concate- 

 nation of phenomena here indicated. The 

 views of modern geognosy lead off from mere 

 hypothesis, which trifles or plays with its sub- 

 ject, and seeks to explain, severally and apart, 

 every manifestation of force of the old globe ; 

 they shew the connection of the various matters 

 ejected with what appertains only to change in 

 reference to space — concussion, elevation, de- 

 pression ; they arrange side by side groups of 

 phenomena which at first sight present them- 

 selves as extremely heterogeneous — thermal 

 springs, effusions of carbonic acid gas, escapes 

 of sulphureous vapours, harmless eruptions of 

 mud, and the awful devastations of burning 

 mountains. In a grand picture of nature all 

 this becomes fused in the single conception of 

 the reaction of the interior of a planet upon its 

 crust and surface. So do we recognize in the 

 depths of the earth, in its temperature increas- 

 ing with the distance from the surface, at once 

 the germs of concussive movements, of the 

 gradual elevation of entire continents, or of 

 mountain chains through lengthened chasms, 

 of volcanic eruptions, and of the varied produc 

 tion of mineral species and rocky masses. Buf 

 it is not inorganic nature alone that has felt the 

 force of this reaction of the interior upon the 

 exterior. It is extremely probable that in the 

 primitive world immense discharges of carbonii 

 acid gas mingled with the atmosphere, excitea 

 the faculty possessed by vegetables of separa 

 ting carbon from the air, and that thus, in rev 

 olutions which destroyed extensive forests, in 

 exhaustible supplies of combustible matter — 

 lignites and coals of different kinds — have been 

 buried beneath the upper strata of the earth. 

 The destiny of man we even recognize as m 

 part dependent on the fashion of the outer crast 

 of the globe, on the partitioning of continents, 

 on the direction of their mountain chains unc* 

 high lands. To the inquiring spirit is it givet 

 to mount from link to link in the chain of phe- 

 nomena, till the point is gained at which in thr« 

 incipient consolidation of our planet, in the firs*" 

 transition of the conglobated matter from tb» 

 vaporous form, the internal heat of the earth, 

 that heat which does not belong to the actioi 

 of the sun, was developed. 



In our survey of the causal connection ot 

 geognostical phenomena, we shall begin witit 

 those which, in their principal features, are dy- 

 namical, which consist in motion and a change 

 in space. Earthquakes of every kind and de- 

 gree are distinguished by a series of perpendic 

 ular, or horizontal, or rotatory vibrations fo* 

 lowing each other in rapid succession. In thf* 

 course of the considerable number of earth 

 quakes which I have felt in both hemisphere* 

 of the globe, on shore and at sea, the two firs< 

 kinds of motion have appeared to me very fre- 

 quently to take place together. The explosiv** 



