“Reflections concerning earthquakes Part III”

Date

3-11-1812

Newspaper

The Georgia Journal

Page and Column

Page 3, column 2, 3, and 4

Newspaper Location

Milledgeville, Georgia

Serial Number

600

Abstract

Another article from Capac concerning earthquake origins.

Transcript

FOR THE GEORGIA JOURNAL. REFLECTIONS CONCERNING EARTHQUAKES. No. III. Of the mechanism of Earthquakes. As we regard Earthquakes as the consequence of the expansive force of classic vapors, it is proper that we make some enquiry into the circumstances that direct this power to the production of its various effects. If an elastic vapor is confined in a cavity less than it would occupy if at liberty, it exerts on all sides an expansive force, which beyond doubt may be and frequently is the most powerful engine that ever exerts its force on the earth. This force being on all sides equal, if it is exerted below the surface of the earth, that part which offers last resistance, will yield first to its power; in which case an enlargement or bursting of the cavity is effected. When in this way the surface of the earth is ruptured, especially if it happens suddenly, an undulatory motion is produced, the extent of which varies in conformity with the circumstances under which it happens. When the rupture happens perpendicularly, or in a direct line from the earth's centre to its surface, motion will be communicated on all sides horizontally, in the same manner that circular waves are raised on water by the falling of a heavy body on its surface; the extent and celerity of this motion will be greater in proportion to the density of the matter through which it passes. If the surface of the earth is ruptured by the same force at two places, the land in the intermediate space losing its support, may sink below its usual height, and in closing, the parts that were previously at some distance, may come in apposition, and if this does not happen the excavation is filled with water. Examples of which may be found in the sinking of the Andes, and of the province in Asia. When a horizontal enlargement is made in a cavity of the earth, it may extend to a great distance without our perceiving its effect on the earth's surface; but if in its progress the earth's surface descends so low as to meet the line in which it passes, an explosion happens, and there is a synchronous motion produced in all the superincumbent earth, as by its gravity it descends to the place from which it was forced. The elastic vapor having escaped and the surface of the earth regained its former position, the same process may be repeated. On this principle the late shocks in the United States admit of explanation. Our country seems to be founded on a stratum of granite running from North East to South West under which the expansive vapor might have been confined and conducted to an outlet in the Pacific or Frozen ocean. But in accounting for these it is not necessary to suppose that there is a cavity of very great extent in the earth. Motion, when commenced in the earth, is conveyed to as much greater distance, & with as much more celerity, than it is in the air as of the earth is more dense than the fluid. If this is true, and the motion produced in the air by the blowing of a horn is conveyed a mile in little more than four seconds, how immense, must be the difference between the time and distance of conveyance of a similar motion commenced in the earth. Motion commenced in the air becomes less as it recedes from its origin; the same is true of the earth, but this also is in conformity with the above rules; so that on the earth it would be conveyed to a great distance without a perceptible difference in its force, or the time of its happening.-But when inequality in the surface of the earth, proceeds as low as the origin of volcanic explosions, the motion is conveyed no further; from which it is easy to perceive that violent earthquakes may happen on islands and not extend to continents, and on these without extending beyond their own boundary. There is notwithstanding reason to believe that the whole earth has been shaken by earthquakes, and that which was attended with the sinking of Lisbon, is well known to have been felt in America. Before I leave the subject, I think it proper to mention a theory of earthquakes, that is not without votaries of respectability. They are believed to depend on the restoration of the equilibrium in the electric matter that is proper to the atmosphere and the earth. What are the reasons in support of this opinion? Is it proven that this disparity of electricity ever happens? Should it happen, would the restoration of its equilibrium be instantaneous? And if suddenly restored, would an earthquake be the consequence? None of these queries can be answered in the affirmative. Since it has been rendered probable that lightning depends on electricity, its influence has been sought for in all the grand operations of nature: But our knowledge of the subjects is so limited, that opinions not grounded on experiments, are not worthy of belief, only a few facts are known concerning it, and why, in the pursuit of an imaginary power, should we grope in a labyrinth of darkness, when by another route we are allowed at least the faint glimmering of a taper. These few hints may serve to assist persons in their reflections on this subject; but I cannot bid it adieu without indulging in some reflections which it seems to suggest. We are naturally led to enquire into the possible effect of these phenomena on the earth. Can we suppose with Dr. Darwin that the Moon was originally a constitutents were raised from the depths of the ocean, by the expansive force of internal fires? Common sense seems to reject such a theory. But the tops of the Andes and other very high mountains were once covered by the waters of the ocean as appears from the numerous shells of maritime animals that are found on them. Where is now the water that once raised the ocean to that height? and where at that time was the habitation of man? All is conjecture! It must be acknowledged, that the facts we have in possession, are sufficient to bewilder us. Then let us view the earth only for the purpose of ascertaining facts, without hoping at present to effect their explanation. Till, by comparing these, we are enabled to form something like a plausible theory; let us, as it seems rational, believe that the continents of the earth have their basis on its centre; that the nature of their constituent parts is such that however they may be removed they will still remain above the surface of the ocean; and that the laws of nature, by which parts of the earth are precipitated to "the great deep" are as necessary for its general preservation, as those by which other parts are supported. But however confident we may be in these opinions, when we feel the earth rocking to and fro like a drunkard the unavoidably experience sensations that are awfully sublime, and terrible it is that we feel, as if we knew ourselves, in the immediate presence of God, and beheld the greatest stretch of his power exercised on the earth. But alas, vain man! how long is it before thou will learn that thy ideas of the greatness of this operation are drawn entirely from thy own insignificance, that in the hour in which thou thinkest that they God has the world, or thy country under the immediate stroke of his power; he dwells in the "calm fields of the rest." An unconcerned spectator of the works of his hands; "equal eye as god of all, A hero perish, or a sparrow fall; Atoms or systems into ruin hurled? An now a bubble burst, and now a world." It we admit our sister planets to be terraneous globes, what idea do we attach to earthquakes when they happen on them. They are, in our fancy, but slight oscillations, or changes in their surfaces, whereby a portion of earth approaches nearer then centre; if the place is the habitation of men; their place of abode, is only a point, in our fancy, and they themselves as insects. Yet in the scale of creation we are not, superior to them; however we maybe persuaded by our fancy that our world is the centre of the universe, and ourselves the top pieces of creation. These extravagancies depend entirely on the narrowness of our minds, and we have reason to say with the humility and devotion of David;--"When I consider thy Heavens, the works of they fingers, the moon and stars, which thou has ordained:--Lord what is man that thou art mindful of him and the son of man that thou visitest him."

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