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had won for himself, by his unwearied striving, a new and nobler nature, and taken a high place among the instructors and best benefactors of mankind. This alone is true happiness-the one worthy end of human exertion or ambition-the only satisfying reward of all labour, and study, and virtuous activity or endurance. Among the shipmates with whom Cook mixed when he first went to sea, there was perhaps no one who ever either raised himself above the condition to which he then belonged in point of outward circumstances, or enlarged in any considerable degree the knowledge or mental resources he then possessed. And some will perhaps say that this was little to be regretted, at least on their own account; that the many who spent their lives in their original sphere were probably as happy as the one who succeeded in rising above it; but this is, indeed, to cast a hasty glance on human life and human nature. That man was never truly happy-happy upon reflection, and while looking to the past or the future—who could not say to himself that he had made something of the faculties God gave him, and had not lived altogether without progression, like one of the inferior animals. We do not speak of mere wealth or station; these are comparatively nothing; are as often missed as attained, even by those who best merit them; and do not of themselves constitute happiness when they are possessed. But there must be some consciousness of an intellectual or moral progress, or there can be no satisfaction, no self-congratulation on reviewing what of life may be already gone, no hope in the prospect of what is yet to come. All men feel this, and feel it strongly; and if they could secure for themselves the source of happiness in question by a wish, would avail themselves of the privilege with sufficient alacrity. Nobody would pass his life in ignorance, if knowledge might be had by merely looking up to the clouds for it it is the labour necessary for its acquirement that scares them; and this labour they have not resolution to encounter. Yet it is, in truth, from the exertion by which it must be obtained that knowledge derives at least half its value; for to this entirely we owe the sense of merit in ourselves which the acquisition brings along with it; and hence no little of the happiness of which we have just described its possession to be the source; besides that, the labour itself soon becomes an enjoyment.' Let these observations meet with a ready reception among youth, in whatever rank in life. Honour and fame are not to be achieved by seeking for them alone, nor are their possession the end and aim of human existence. It is only by an unwearied striving after a new and nobler nature; only by being useful to our fellows, and making the most of those qualities of mind which God has given us, that happiness is to be attained, or that we fulfil the ends of our being.

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N such a country as Britain, where from time immemorial the outlines of hill and valley have remained the same, we instinctively look upon the solid earth on which we tread as a kind of type or standard of durability. The sky is ever changing; the sea is never at rest; the brook, the river, the cataract, the lake are swollen by the storm or dried up by the drought; but the firm framework of the land seems to lie motionless all the while. True, if we watch, we shall find that its surface, even where it consists of the hardest rock, is slowly crumbling away, that it cannot resist the universal process of change which runs through nature. Yet, after all, this decay affects merely the outer skin, and its advance seems to most men so slow that it is not taken into account. Beneath the wasting surface, the solid foundations of the country seem to stand century after century firm as at the first.

So deeply is this faith in the stability of the dry land fixed in the mind, that comparatively few of us ever adequately realise that the tranquillity might come to an end, and that the firm earth on which we and our forefathers have for generations built our cities and towns, might heave and break open under our feet, and our cities

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No. 42.

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might be tossed into ruins. Hardly a year passes, indeed, without tremors of greater or less distinctness being felt in some part of England. Sometimes we read in the papers that throughout the western counties an underground rumbling, as of thunder, has been heard, houses have been shaken, and the inhabitants startled out of sleep; at other times, accounts from the north tell of the rocking of beds, the jingling of dishes, the tinkling of bells, or even of the fall of plaster from walls or ceilings. The narratives are duly read, a little curiosity is excited, and in a few days the subject passes out of mind.

Within the period embraced by human history and tradition, no volcanic eruption nor any earthquake shock of magnitude has been witnessed in the British Islands; we have happily escaped from any visitation of one of the most dreadful calamities which can befall us. And yet there was a time, which, in a geological sense, is not very remote, when a line of volcanos blazed all along the north-west of Britain, and extended even onwards to Iceland. The subterranean fires have for the present died out. We may wander among the old lava-beds and ashes without perhaps ever suspecting what has really been their origin. No hot springs rise from them, nor emanations of gas, such as occur in some districts of extinct volcanos. They have been wasted by the elements, carved into picturesque glens and ravines and mountains, and all trace of their early contour has been wholly effaced. We have, however, no good reason for asserting, or even for suspecting, that the underground forces have finally died out in our region, and that no future volcano or great earthquake is possible. In the past geological history of this country there have been many volcanic periods separated from each other by vast intervals of tranquillity. It is quite possible that the present is another of these intervals, and that the volcanic forces may break out again. From the bygone history of our country, therefore, as well as from its possible future, we have good grounds for taking an interest in all that relates to underground movements.

The present short paper proposes to give a sketch of the effects produced on the surface of the earth by the action of forces which are lodged within the interior. We shall first consider the phenomena of sudden movements, or what are known as earthquakes; next, the nature of volcanos; and lastly, the gradual rising or sinking of wide tracts of land or sea-bed. Having examined these phenomena separately, we may then look at them as a whole, and glance at the theories which have been proposed to account for them.

EARTHQUAKES.

The term earthquake is loosely applied to all subterranean noises or tremors, whether of so slight a kind as to be hardly perceptible, or so violent as to cause vast destruction, and permanently to

alter the face of the earth. Sometimes all that is felt is an indistinct underground rumbling like that of distant thunder, or of a heavily laden wagon drawn along a causeway. Such noises are often

experienced in countries where they are the only evidence of any movement or action going on within the crust of the earth. In Britain, for example, probably no year passes without examples having occurred in different parts of the country, affecting perhaps a whole county or parts of several counties, though not extending over the whole island. From such feeble indications, we can trace a gradual increase of intensity until we reach the great earthquake, when the ground rocks to and fro like a billowy sea, the earth is rent open, cities are reduced to ruins, and the sea is driven with fearful violence over the land. All the different stages of this series of underground movements are classed under the general name of Earthquakes.

It is now well known that the force which produces an earthquake radiates from a central point, in what might be called undulating waves; and that the strength of the undulations, and also the distance to which they proceed, depend on the nature of the rocky strata operated upon. The looser and less elastic the medium, the slower is the rate of motion of the wave; and, on the other hand, the more elastic, homogeneous, and free from fissures the rock is, the more rapidly does it allow the undulations to pass through

its mass.

It has been estimated that the earthquake of Lisbon in 1755 travelled on an average at the rate of 1760 feet in a second. This calculation, however, is merely a rough one, founded on the recorded time at which the shock was felt at different places in the same line of divergence from Lisbon. More accurate observations of the Calabrian earthquake of 1857 gave a rate of about 820 feet per second. It is evident that where the rocks underneath the surface differ greatly among themselves in compactness, and where, even when tolerably uniform in texture, they are broken up by many fissures, the earthquake wave, as it spreads outward, will be constantly varying both in speed and in direction.

Mr Mallet, who has contributed so much to our knowledge of the dynamics of earthquakes, has endeavoured to ascertain the depth at which these concussions take their origin. He believes that there is some point or focus whence the movement is transmitted straight up to the surface. Directly over this focus the shock is first felt, and is recognised as coming up perpendicularly. As we recede from it, we find the angle of emergence of the earth-wave to grow less and less inclined, until the vibration appears to be spreading horizontally outwards, like the rings round the spot where a stone has descended upon the surface of a pool of water. If, now, we can accurately fix, first the central point where the wave has ascended vertically, and then some point outside where the wave has come up

at a certain measured angle, two straight lines drawn in the path of the wave from these two points downward will meet at a certain distance below ground, which will be the point or focus from which the vibration or earth-wave took its rise. Mr Mallet visited Calabria after the great earthquake of December 1857, and succeeded in making a number of observations, from which he arrived at the conclusion that the seat of that earthquake was probably somewhere about seven or eight miles below the surface. He has been led to the belief that earthquake phenomena generally are not to be traced to the operation of forces acting deep within the central mass of the earth, but that, viewed on the great scale, they are quite superficial, never perhaps having their source at a greater depth than thirty miles.

Let us now endeavour to follow the changes which an earthquake brings with it.

The occurrence of a violent earthquake is sometimes preceded by peculiar states of the atmosphere, which, though their meaning may be wholly unguessed at the time, are afterwards connected with the subterranean commotions. Great heat and closeness of the atmosphere, sudden gusts of wind, heavy rains, thunder-storms and other electric discharges, have been observed to occur before an earthquake. But these portents are seldom such as to cause any disquietude at the time, or to furnish any sure prognostication as to whether an earthquake is about to take place; they acquire all their interest from the events which follow them. In the case of a slight shock, a long, low, rumbling noise is sometimes heard in advance, variously compared to the muttering of distant thunder, the discharge of artillery, the growl of a tempest, the roll of heavily laden wagons, the explosion of a mine or of a powder-work, and even to the whistling of a locomotive steam-engine. Windows, glasses, pictures, and other loose objects shake and jingle, doors creak or open, and the inhabitants, who have probably often had experience of these portents, know that it is an earthquake. Sometimes nothing more takes place, and after some anxiety, the people return to their vocations.

Movements of this kind are in many countries the only forms of subterranean movement which have been known within human memory. In Britain, for example, many hundreds of cases are recorded as having taken place in different parts of the country. In the first forty years of the present century, at least two hundred shocks of greater or less consequence occurred. Most of these were observed in Scotland, particularly throughout the southern and central parts of the Highlands. But smart shocks were likewise experienced in the north of England, in the central and southwestern counties, as well as in the south and south-west of Ireland. During that interval, too, the tremors of the ground seemed to come, as it were, by fits and starts. For a year or two, hardly any, and

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