Part 14

But this is little. Wonderful as is the extent of the sidereal system as thus viewed, even more wonderful is its infinite variety. We know how largely modern discoveries have increased our estimate of the complexity of the planetary system. Where the ancients recognized but a few planets, we now see, besides the planets, the families of satellites; we see the rings of Saturn, in which minute satellites must be as the sands on the sea-shore for multitude; the wonderful zone of asteroids; myriads on myriads of comets; millions on millions of meteor-systems, gathering more and more richly around the sun, until in his neighbourhood they form the crown of glory which bursts into view when he is totally eclipsed. But wonderful as is the variety seen within the planetary system, the variety within the sidereal system is infinitely more amazing. Besides the single suns, there are groups and systems and streams of primary suns; there are whole galaxies of minor orbs; there are clustering stellar aggregations, showing every variety of richness, of figure, and of distribution; there are all the various forms of nebulæ, resolvable and irresolvable, circular, elliptical, and spiral; and lastly, there are irregular masses of luminous gas, clinging in fantastic convolutions around stars and star-systems. Nor is it unsafe to assert that other forms and variety of structure will yet be discovered, or that hundreds more exist which we may never hope to recognize.

But lastly, even more wonderful than the infinite variety of the sidereal system, is its amazing vitality. Instead of millions of inert masses, we see the whole heavens instinct with energy—astir with busy life. The great masses of luminous vapour, though occupying countless millions of cubic miles of space, are moved by unknown forces like clouds before the summer breeze; star-mist is condensing into clusters; star-clusters are forming into suns; streams and clusters of minor orbs are swayed by unknown attractive energies; and primary suns singly or in systems are pursuing their stately path through space, rejoicing as giants to run their course, extending on all sides the mighty arm of their attraction, gathering from ever-new regions of space supplies of motive energy, to be transformed into the various forms of force—light and heat and electricity—and distributed in lavish abundance to the worlds which circle round them.

Truly may I say, in conclusion, that whether we regard its vast extent, its infinite variety, or the amazing vitality which pervades its every portion, the sidereal system is, of all the subjects man can study, the most imposing and the most stupendous. It is as a book full of mighty problems—of problems which are as yet almost untouched by man, of problems which it might seem hopeless for him to attempt to solve. But those problems are given to him for solution, and he _will_ solve them, whenever he dares attempt to decipher aright the records of that wondrous volume.

_MALLET’S THEORY OF VOLCANOES._

There are few subjects less satisfactorily treated in scientific treatises than that which Humboldt calls the Reaction of the Earth’s Interior. We find, not merely in the configuration of the earth’s crust, but in actual and very remarkable phenomena, evidence of subterranean forces of great activity; and the problems suggested seem in no sense impracticable: yet no theory of the earth’s volcanic energy has yet gained general acceptance. While the astronomer tells us of the constitution of orbs millions of times further away than our own sun, the geologist has hitherto been unable to give an account of the forces which agitate the crust of the orb on which we live.

The theory put forward respecting volcanic energy, however, by the eminent seismologist Mallet, 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 previously enunciated. 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 briefly 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 certain 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 unfamiliar 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 exhausted before the surface was consolidated.

Another inviting theory is that according to which the earth is regarded as a mere shell of solid matter surrounding a molten nucleus. 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 physicists 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 glutinous liquids, while the structural 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 mathematician Hopkins, whose analysis of the molten-nucleus theory was mainly effective in showing that theory to be untenable, suggested that there may be isolated subterranean lakes of fiery 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 undoubtedly 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 contraction 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 relatively 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 elevation 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 elevations 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 ridges 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 of 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 expended 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 fusion. The access of water to such points determines volcanic eruption.”

Now all this is not mere theorising. Mr. Mallet does not come before the scientific world with an ingenious speculation, 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 precisely 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 annually 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 peculiarities of the earth’s surface configuration. Few that have studied carefully drawn charts of the chief mountain-ranges can have failed to notice that the arrangement of these ranges does not accord with the idea of upheaval 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. Mallet has indicated. The shrivelled skin of an apple affords no inapt representation of the corrugated surface of our earth, and according to the new theory, the shrivelling of such a skin is precisely analogous 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 strata 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 worthy of notice that Mr. Mallet’s theory of Volcanic energy is completely opposed to ordinary ideas respecting earthquakes and volcanoes. We have been accustomed vaguely 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 exterior. 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 geologists 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 remains 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 astronomers that the earth might explode like a bomb, her scattered fragments producing a ring of bodies resembling the zone of asteroids, seems further than ever from probability; if ever there was any danger of such a catastrophe, the danger has long since passed away.

_TOWARDS THE NORTH POLE._

The Arctic Expedition which returned to our shores in the autumn of 1876 may be regarded as having finally decided the question whether the North Pole of the earth is accessible by the route through Smith’s Sound—a route which may conveniently and properly be called the American route. Attacks may hereafter be made on the Polar fastness from other directions; but it is exceedingly unlikely that this country, at any rate, will again attempt to reach the Pole along the line of attack followed by Captain Nares’s expedition. I may be forgiven, perhaps, for regarding Arctic voyages made by the seamen of other nations as less likely to be successful than those made by my own countrymen. It is not mere national prejudice which suggests this opinion. It is the simple fact that hitherto the most successful approaches towards both the Northern and the Southern Poles have been made by British sailors. Nearly a quarter of a century has passed since Sir E. Parry made the nearest approach to the North Pole recorded up to that time; and although, in the interval between Parry’s expedition and Nares’s, no expedition had been sent out from our shores with the object of advancing towards the Pole, while America, Sweden, Russia, and Germany sent out several, Parry’s attempt still remained unsurpassed and unequalled. At length it has been surpassed, but it has been by his own countrymen. In like manner, no nation has yet succeeded in approaching the Antarctic Pole so nearly, within many miles, as did Captain Sir J. C. Ross in 1844. Considering these circumstances, and remembering the success which rewarded the efforts of Great Britain in the search for the North-West Passage, it cannot be regarded as national prejudice to assert that events indicate the seamen of this country as exceptionally fitted to contend successfully against the difficulties and the dangers of Arctic exploration. Should England, then, give up the attempt to reach the North Pole by way of Smith’s Sound and its northerly prolongation, it may fairly be considered unlikely that the Pole will ever be reached in that direction.

It may be well to examine the relative probable chances of success along other routes which have either not been so thoroughly tried, or have been tried under less favourable conditions.

Passing over the unfortunate expedition under Hugh Willoughby in 1553, the first attempt to penetrate within the Polar domain was made by Henry Hudson in 1607. The route selected was one which many regard (and I believe correctly) as the one on which there is the best chance of success; namely, the route across the sea lying to the west of Spitzbergen. That Hudson, in the clumsy galleons of Elizabeth’s time, should have penetrated to within eight degrees and a half of the Pole, or to a distance only exceeding Nares’s nearest approach by about 130 miles, proves conclusively, we think, that with modern ships, and especially with the aid of steam, this route might be followed with much better prospect of success than that which was adopted for Nares’s expedition. If the reader will examine a map of the Arctic regions he will find that the western shores of Spitzbergen and the north-eastern shores of Greenland, as far as they have been yet explored, are separated by about 33 degrees of longitude, equivalent on the 80th parallel of latitude to about 335 miles. Across the whole breadth of this sea Arctic voyagers have attempted to sail northwards beyond the 80th parallel, but no one has yet succeeded in the attempt except on the eastern side of that sea. It was here that Hudson—fortunately for him—directed his attack; and he passed a hundred miles to the north of the 80th parallel, being impeded and finally stopped by the packed ice around the north-western shores of Spitzbergen.

Let us consider the fortunes of other attempts which have been made to approach the Pole in this direction.

In 1827 Captain (afterwards Sir Edward) Parry, who had already four times passed beyond the Arctic Circle—viz., in 1818, 1819, 1821–23, and 1824–25—made an attempt to reach the North Pole by way of Spitzbergen. His plan was to follow Hudson’s route until stopped by ice; then to leave his ship, and cross the ice-field with sledges drawn by Esquimaux dogs, and, taking boats along with the party, to cross whatever open water they might find. In this way he succeeded in reaching latitude 82° 45´ north, the highest ever attained until Nares’s expedition succeeded in crossing the 83rd parallel. Parry found that the whole of the ice-field over which his party were laboriously travelling northwards was being carried bodily southwards, and that at length the distance they were able to travel in a day was equalled by the southerly daily drift of the ice-field, so that they made no real progress. He gave up further contest, and returned to his ship the _Hecla_.

It is important to inquire whether the southerly drift which stopped Parry was due to northerly winds or to a southerly current; and if to the latter cause, whether this current probably affects the whole extent of the sea in which Parry’s ice-field was drifting. We know that his party were exposed, during the greater part of their advance from Spitzbergen, to northerly winds. Now the real velocity of these winds must have been greater than their apparent velocity, because the ice-field was moving southwards. Had this not been the case, or had the ice-field been suddenly stopped, the wind would have seemed stronger; precisely as it seems stronger to passengers on board a sailing vessel when, after being before the wind for a time, she is brought across the wind. The ice-field was clearly travelling before the wind, but not nearly so fast as the wind; and therefore there is good reason for believing that the motion of the ice-field was due to the wind alone. If we suppose this to have been really the case, then, as there is no reason for believing that northerly winds prevail uniformly in the Arctic regions, we must regard Parry’s defeat as due to mischance. Another explorer might have southerly instead of northerly winds, and so might be assisted instead of impeded in his advance towards the Pole. Had this been Parry’s fortune, or even if the winds had proved neutral, he would have approached nearer to the Pole than Nares. For Parry reckoned that he had lost more than a hundred miles by the southerly drift of the ice-field, by which amount at least he would have advanced further north. But that was not all; for there can be little doubt that he would have continued his efforts longer but for the Sisyphæan nature of the struggle. It is true he was nearer home when he turned back than he would have been but for the drift, and one of his reasons for turning back was the consideration of the distance which his men had to travel in returning. But he was chiefly influenced (so far as the return journey was concerned) by the danger caused by the movable nature of the ice-field, which might at any time begin to travel northwards, or eastwards, or westwards.

If we suppose that not the wind but Arctic currents carried the ice-field southwards, we must yet admit the probability—nay, almost the certainty—that such currents are only local, and occupy but a part of the breadth of the North Atlantic seas in those high latitudes. The general drift of the North Atlantic surface-water is unquestionably not towards the south but towards the north; and whatever part we suppose the Arctic ice to perform in regulating the system of oceanic circulation—whether, with Carpenter, we consider the descent of the cooled water as the great moving cause of the entire system of circulation, or assign to that motion a less important office (which seems to me the juster opinion)—we must in any case regard the Arctic seas as a region of surface indraught. The current flowing from those seas, which caused (on the hypothesis we are for the moment adopting) the southwardly motion of Parry’s ice-field, must therefore be regarded as in all probability an exceptional phenomenon of those seas. By making the advance from a more eastwardly or more westwardly part of Spitzbergen, a northerly current would probably be met with; or rather, the motion of the ice-field would indicate the presence of such a current, for I question very much whether open water would anywhere be found north of the 83rd parallel. In that case, a party might advance in one longitude and return in another, selecting for their return the longitude in which (always according to our present hypothesis that currents caused the drift) Parry found that a southerly current underlay his route across the ice. On the whole, however, it appears to me more probable that winds, not currents, caused the southerly drift of Parry’s ice-field.

In 1868, a German expedition, under Captain Koldewey, made the first visit to the seas west of Spitzbergen in a steamship, the small but powerful screw steamer _Germania_ (126 tons), advancing northwards a little beyond the 81st parallel. But this voyage can scarcely be regarded as an attempt to approach the Pole on that course; for Koldewey’s instructions were, “to explore the eastern coast of Greenland northwards; and, if he found success in that direction impossible, to make for the mysterious Island of Gilles on the east of Spitzbergen.”

Scoresby in 1806 had made thus far the most northerly voyage in a ship on Hudson’s route, but in 1868 a Swedish expedition attained higher latitudes than had ever or have ever been reached by a ship in that direction. The steamship _Sofia_, strongly built of Swedish iron, and originally intended for winter voyages in the Baltic, was selected for the voyage. Owing to a number of unfortunate delays, it was not until September, 1868, that the _Sofia_ reached the most northerly part of her journey, attaining a point nearly fifteen miles further north than Hudson had reached. To the north broken ice was still found, but it was so closely packed that not even a boat could pass through. Two months earlier in the season the voyagers might have waited for a change of wind and the breaking up of the ice; but in the middle of September this would have been very dangerous. The temperature was already sixteen degrees below the freezing-point, and there was every prospect that in a few weeks, or even days, the seas over which they had reached their present position would be icebound. They turned back from that advanced position; but, with courage worthy of the old Vikings, they made another attack a fortnight later. They were foiled again, as was to be expected, for by this time the sun was already on the wintry side of the equator. They had, indeed, a narrow escape from destruction. “An ice-block with which they came into collision opened a large leak in the ship’s side, and when, after great exertions, they reached the land, the water already stood two feet over the cabin floor.”[21]