The theory put forward respecting volcanic energy, however, by the eminent13 seismologist Mallet14, promises not merely to take the place of all others, but to gain a degree of acceptance which has not been accorded to any theory previously15 enunciated16. It is, in principle, exceedingly simple, though many of the details (into which I do not propose to enter) involve questions of considerable difficulty.
Let us, in the first place, consider briefly17 the various explanations which had been already advanced.
There was first the chemical theory of volcanic energy, the favourite theory of Sir Humphry Davy. It is possible to produce on a small scale nearly all the phenomena due to subterranean activity, by simply bringing together certain152 substances, and leaving them to undergo the chemical changes due to their association. As a familiar instance of explosive action thus occasioned, we need only mention the results experienced when any one unfamiliar18 with the methods of treating lime endeavours over hastily to “slake” or “slack” it with water. Indeed, one of the strong points of the chemical theory consisted in the circumstance that volcanoes only occur where water can reach the subterranean regions—or, as Mallet expresses it, that “without water there is no volcano.” But the theory is disposed of by the fact, now generally admitted, that the chemical energies of our earth’s materials were almost wholly exhausted19 before the surface was consolidated20.
Another inviting21 theory is that according to which the earth is regarded as a mere2 shell of solid matter surrounding a molten nucleus22. There is every reason to believe that the whole interior of the earth is in a state of intense heat; and if the increase of heat with depth (as shown in our mines) is supposed to continue uniformly, we find that at very moderate depths a degree of heat must prevail sufficient to liquefy any known solids under ordinary conditions. But the conditions under which matter exists a few miles only below the surface of the earth are not ordinary. The pressure enormously exceeds any which our physicists23 can obtain experimentally. The ordinary distinction between solids and liquids cannot exist at that enormous pressure. A mass of cold steel could be as plastic as any of the glutinous24 liquids, while the structural25 change which a solid undergoes in the process of liquefying could not take place under such pressure even at an enormously high temperature. It is now generally admitted that if the earth really has a molten nucleus, the solid crust must, nevertheless, be far too thick to be in any way disturbed by changes affecting the liquid matter beneath.
Yet another theory has found advocates. The mathematician26 Hopkins, whose analysis of the molten-nucleus theory was mainly effective in showing that theory to be untenable,153 suggested that there may be isolated27 subterranean lakes of fiery28 matter, and that these may be the true seat of volcanic energy. But such lakes could not maintain their heat for ages, if surrounded (as the theory requires) by cooler solid matter, especially as the theory also requires that water should have access to them. It will be observed also that none of the theories just described affords any direct account of those various features of the earth’s surface—mountain ranges, table-lands, volcanic regions, and so on—which are undoubtedly29 due to the action of subterranean forces. The theory advanced by Mr. Mallet is open to none of these objections. It seems, indeed, competent to explain all the facts which have hitherto appeared most perplexing.
It is recognized by physicists that our earth is gradually parting with its heat. As it cools it contracts. Now if this process of contraction30 took place uniformly, no subterranean action would result. But if the interior contracts more quickly than the crust, the latter must in some way or other force its way down to the retreating nucleus. Mr. Mallet shows that the hotter internal portion must contract faster than the relatively31 cool crust; and then he shows that the shrinkage of the crust is competent to occasion all the known phenomena of volcanic action. In the distant ages when the earth was still fashioning, the shrinkage produced the irregularities of level which we recognize in the elevation32 of the land and the depression of the ocean-bed. Then came the period when as the crust shrank it formed corrugations, in other words, when the foldings and elevations33 of the somewhat thickened crust gave rise to the mountain-ranges of the earth. Lastly, as the globe gradually lost its extremely high temperature, the continuance of the same process of shrinkage led no longer to the formation of ridges34 and table-lands, but to local crushing-down and dislocation. This process is still going on, and Mr. Mallet not only recognizes here the origin of earthquakes, and of the changes of level now in progress, but the true cause of154 volcanic heat. The modern theory of heat as a form of motion here comes into play. As the solid crust closes in upon the shrinking nucleus, the work expended35 in crushing down and dislocating the parts of the crust is transformed into heat, by which, at the places where the process goes on with greatest energy, “the materials of the rock so crushed and of that adjacent to it are heated even to fusion36. The access of water to such points determines volcanic eruption37.”
Now all this is not mere theorising. Mr. Mallet does not come before the scientific world with an ingenious speculation38, which may or may not be confirmed by observation and experiment. He has measured and weighed the forces of which he speaks. He is able to tell precisely39 what proportion of the actual energy which must be developed as the earth contracts is necessary for the production of observed volcanic phenomena. It is probable that nine-tenths of those who have read these lines would be disposed to think that the contraction of the earth must be far too slow to produce effects so stupendous as those which we recognize in the volcano and the earthquake. But Mr. Mallet is able to show, by calculations which cannot be disputed, that less than one-fourth of the heat at present annually40 lost by the earth is sufficient to account for the total annual volcanic action, according to the best data at present in our possession.
As I have said, I do not propose to follow out Mr. Mallet’s admirable theory into all its details. I content myself with pointing out how excellently it accounts for certain peculiarities41 of the earth’s surface configuration. Few that have studied carefully drawn42 charts of the chief mountain-ranges can have failed to notice that the arrangement of these ranges does not accord with the idea of upheaval43 through the action of internal forces. But it will be at once recognized that the aspect of the mountain-ranges accords exactly with what would be expected to result from such a process of contraction as Mr. Mallet155 has indicated. The shrivelled skin of an apple affords no inapt representation of the corrugated44 surface of our earth, and according to the new theory, the shrivelling of such a skin is precisely analogous45 to the processes at work upon the earth when mountain-ranges were being formed. Again, there are few students of geology who have not found a source of perplexity in the foldings and overlappings of strata46 in mountainous regions. No forces of upheaval seem competent to produce this arrangement. But by the new theory this feature of the earth’s surface is at once explained; indeed, no other arrangement could be looked for.
It is worthy47 of notice that Mr. Mallet’s theory of Volcanic energy is completely opposed to ordinary ideas respecting earthquakes and volcanoes. We have been accustomed vaguely48 to regard these phenomena as due to the eruptive outbursting power of the earth’s interior; we shall now have to consider them as due to the subsidence and shrinkage of the earth’s exterior49. Mountains have not been upheaved, but valleys have sunk down. And in another respect the new theory tends to modify views which have been generally entertained in recent times. Our most eminent geologists50 have taught that the earth’s internal forces may be as active now as in the epochs when the mountain-ranges were formed. But Mr. Mallet’s theory tends to show that the volcanic energy of the earth is a declining force. Its chief action had already been exerted when mountains began to be formed; what remains51 now is but the minutest fraction of the volcanic energy of the mountain-forming era; and each year, as the earth parts with more and more of its internal heat, the sources of her subterranean energy are more and more exhausted. The thought once entertained by astronomers52 that the earth might explode like a bomb, her scattered53 fragments producing a ring of bodies resembling the zone of asteroids54, seems further than ever from probability; if ever there was any danger of such a catastrophe55, the danger has long since passed away.
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1
treatises
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| n.专题著作，专题论文，专著( treatise的名词复数 ) | |
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mere
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| adj.纯粹的；仅仅，只不过 | |
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configuration
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| n.结构，布局，形态，(计算机)配置 | |
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remarkable
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| adj.显著的，异常的，非凡的，值得注意的 | |
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phenomena
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| n.现象 | |
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subterranean
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| adj.地下的，地表下的 | |
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volcanic
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| adj.火山的；象火山的；由火山引起的 | |
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astronomer
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| n.天文学家 | |
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orb
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| n.太阳；星球；v.弄圆；成球形 | |
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orbs
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| abbr.off-reservation boarding school 在校寄宿学校n.球，天体，圆形物( orb的名词复数 ) | |
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geologist
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| n.地质学家 | |
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agitate
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| vi.(for,against)煽动，鼓动；vt.搅动 | |
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eminent
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| adj.显赫的，杰出的，有名的，优良的 | |
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mallet
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| n.槌棒 | |
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previously
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| adv.以前，先前（地） | |
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enunciated
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| v.（清晰地）发音( enunciate的过去式和过去分词 )；确切地说明 | |
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briefly
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| adv.简单地，简短地 | |
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unfamiliar
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| adj.陌生的，不熟悉的 | |
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exhausted
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| adj.极其疲惫的，精疲力尽的 | |
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consolidated
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| a.联合的 | |
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inviting
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| adj.诱人的，引人注目的 | |
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nucleus
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| n.核，核心，原子核 | |
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physicists
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| 物理学家( physicist的名词复数 ) | |
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glutinous
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| adj.粘的，胶状的 | |
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structural
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| adj.构造的，组织的，建筑（用）的 | |
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mathematician
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| n.数学家 | |
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isolated
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| adj.与世隔绝的 | |
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fiery
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| adj.燃烧着的，火红的；暴躁的；激烈的 | |
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undoubtedly
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| adv.确实地，无疑地 | |
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contraction
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| n.缩略词，缩写式，害病 | |
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relatively
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| adv.比较...地，相对地 | |
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elevation
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| n.高度；海拔；高地；上升；提高 | |
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elevations
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| （水平或数量）提高( elevation的名词复数 )； 高地； 海拔； 提升 | |
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ridges
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| n.脊( ridge的名词复数 )；山脊；脊状突起；大气层的)高压脊 | |
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expended
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| v.花费( expend的过去式和过去分词 )；使用（钱等）做某事；用光；耗尽 | |
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fusion
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| n.溶化；熔解；熔化状态，熔和；熔接 | |
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eruption
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| n.火山爆发；（战争等）爆发；（疾病等）发作 | |
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speculation
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| n.思索，沉思；猜测；投机 | |
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precisely
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| adv.恰好，正好，精确地，细致地 | |
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annually
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| adv.一年一次，每年 | |
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peculiarities
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| n. 特质, 特性, 怪癖, 古怪 | |
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drawn
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| v.拖，拉，拔出；adj.憔悴的，紧张的 | |
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upheaval
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| n.胀起，(地壳)的隆起；剧变，动乱 | |
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corrugated
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| adj.波纹的；缩成皱纹的；波纹面的；波纹状的v.（使某物）起皱褶(corrugate的过去式和过去分词) | |
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analogous
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| adj.相似的；类似的 | |
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46
strata
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| n.地层（复数）；社会阶层 | |
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47
worthy
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| adj.(of)值得的，配得上的；有价值的 | |
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48
vaguely
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| adv.含糊地，暖昧地 | |
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49
exterior
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| adj.外部的，外在的；表面的 | |
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50
geologists
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| 地质学家，地质学者( geologist的名词复数 ) | |
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51
remains
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| n.剩余物，残留物；遗体，遗迹 | |
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52
astronomers
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| n.天文学者，天文学家( astronomer的名词复数 ) | |
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53
scattered
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| adj.分散的，稀疏的；散步的；疏疏落落的 | |
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54
asteroids
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| n.小行星( asteroid的名词复数 )；海盘车，海星 | |
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55
catastrophe
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| n.大灾难，大祸 | |
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