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abounding vitality, now a desolation. But what is the cause of all this? It is only mechanical. The earth's axis of rotation is inclined to the plane of her orbit of revolution round the sun.

Let that wonderful phenomenon and its explanation be a lesson to us; let it profoundly impress us with the importance of physical agents and physical laws. They intervene in the life and death of man personally and socially. External events become interwoven in our constitution; their periodicities create periodicities in us. Day and night are incorporated in our waking and sleeping; summer and winter compel us to exhibit cycles in our life.

depends on

They who have paid attention to the subject have long ago ascertained that the possibility of human Individual existence on the earth depends on conditions existence altogether of a material kind. Since it is only physical conwithin a narrow range of temperature that life ditions. can be maintained, it is needful that our planet should be at a definite mean distance from the source of light and heat, the sun; and that the form of her orbit should be so little eccentric as to approach closely to a circle. if her mass were lager or less than it is, the weight of all living and lifeless things on her surface would no longer be the same; but absolute weight is one of the primary elements of organic construction. A change in the time of her diurnal otation, as affecting the length of the day and night, must at once be followed by a corresponding modification of the periodicities of the nervous system of animals; a change in her orbitual translation round the sun, as determining the duration of the year, would, in like manner, give rise to a marked effect. If the year were

shorter, we should live faster and die sooner.

interbalanced

In the present economy of our globe, natural agents are relied upon as the means of regulation and of Animal and gove: nment. Through heat, the distribution vegetable life and arrangement of the vegetable tribes are by materi.. accomplished; through their mutual relations conditions. with the atmospheric air, plants and animals are interbalanced, and neither permitted to obtain a superiority. Considering the magnitude of this condition, and its

necessity to general life, it might seem worthy of incessant Divine intervention, yet it is in fact accomplished automatically.

And also ap

Of past organic history the same remark may be made. The condensation of carbon from the air, and its inclusion in the strata. constitute the chief epoch in the organic life of the earth, giving a possibility for the pearances and appearance of the hot-blooded and more inextinctions tellectual animal tribes. That great event was determined. occasioned by the influence of the rays of the sun. And as such influences have thus been connected with the appearance of organisms, so likewise have they been concerned in the removal. Of the myriads of species which have become extinct, doub less every one has passed away through the advent of material conditions incompatible with its continuance. Even now, a fall of ha fadozen degrees in the mean temperature of any latitude would occasion the vanishing of the forms of warmer climates, and the advent of those of the colder. obscuration of the rays of the sun for a few years would compel a redistribution of plants and animals all over the earth; many would totally disappear, and everywhere new comers would be seen.

Permanence

of organisms

due to immobility of ex

ternal condi

tions.

An

The permanence of organic forms is altogether dependent on the invariability of the material conditions under which they live. Any variation therein, no matter how insignificant it might be, would be forthwith followed by a corresponding variation in the form. The present invariability of the world of organization is the direct consequence of the physical equilibrium, and so it will continue as long as the inen temperature, the annual supply of light. the composition of the air, the distribution of water, oceanic and atmospheric currents, and other such agencies remain unaltered; but if any one of these, or of a hundred other incidents that might be mentioned, should suffer modification, in an instant the fanciful doctrine of the immutability of species would be brought to its true value. The organic world appears to be in repose, because natural influences have reached an equilibrium. A marble may remain for ever motionless upon a level table; but let the

surface be a little inclined, and the marble will quickly run off. What should we say of him, who, contemplating it in its state of rest, asserted that it was impossible for it ever to move?

lowed by or

changes.

They who can see no difference between the race-horse and the Shetland pony, the bantam and the Shanghai fowl, the greyhound and the poodle dog, who altogether deny that impressions can be made on species, and see in the long succession of extinct forms, the ancient existence of which they must acknowledge, the evidences of a continuous and creative intervention, forget that mundane effects Orderly seobserve definite sequences, event following event quence of conin the necessity of the case, and thus constitu- ditions is folting a chain, each link of which hangs on a pre- derly organic ceding, and holds a succeeding one. Physical influences thus following one another, and bearing to each other the inter-relation of cause and effect, stand in their totality to the whole organic world as causes, it representing the effect, and the order of succession existing among them is perpetuated or embodied in it. Thus, in those ancient times to which we have referred, the sunlight acting on the leaves of plants disturbed the chemical constitution of the atmosphere, gave rise to the accumulation of a more energetic element therein, diminished the mechanical pressure, and changed the rate of evaporation from the sea, a series of events following one another so necessarily that we foresee their order, and, in their turn, making an impression on the vegetable and animal economy. The natural influences, thus varying in an orderly way, controlled botanical events, and made them change correspondingly. The orderly procedure of the one must be imitated in the orderly procedure of the other. And the same holds good in the animal kingdom; the recognized variation in the material conditions is copied in the organic effects, in vigour of motion, energy of life, intellectual power.

When, therefore, we notice such orderly successions, we must not at once assign them to a direct intervention, the issue of wise predeterminations of a voluntary agent; we must first satisfy ourselves how far they are dependent on mundane or material conditions, occurring in a definite

and necessary series, ever bearing in mind the important principle that an orderly sequence of inorganic events necessarily involves an orderly and corresponding progression of organic life.

Universal control of physical

To this doctrine of the control of physical agencies over organic forms I acknowledge no exception, not even in the case of man. The varied aspects he presents in different countries are the necessary organisms. consequences of those influences.

agents over

The case of

man.

He who advocates the doctrine of the unity of the human race is plainly forced to the admission of the absolute control of such agents over the organization of man, since the originally-created type has been brought to exhibit very different aspects in different parts of the world, apparently in accordance with the climate and other purely material circumstances. To those circumstances it is scarcely necessary to add manner of life, for that itself arises from them. The doctrine of unity demands as its essential postulate an admission of the paramount control of physical agents over the human aspect and organization, else how could it be that, proceeding from the same stock, all shades of complexion in the skin, and variety in the form of the skull, should have arisen? Experience assures us that these are changes assumed only by slow degrees, and not with abruptness; they come as a cumulative effect. They plainly enforce the doctrine that national type is not to be regarded as a definite or final thing, a seeming immobility in this particular being due to the attainment of a correspondence with the conditions to which the type is exposed. Let those conditions be changed, and it begins forthwith to change too. I repeat it, therefore, that he who receives the doctrine of the unity of the human race, must al o accept, in view of the present state of humanity on various parts of the surface of our planet, its necessary postulate, the complete control of physical agents. whether natural, or arising artificially from the arts of civilization and the secular progress of nations toward a correspondence with the conditions to which they are exposed.

To the same conclusion a'so must he be brought who advocates the origin of different races from different

centres. It comes to the same thing, whichever of those doctrines we adopt. Each brings us to the admission of the transitory nature of typical forms, to their transmutations and extinctions.

Variations in the aspect of men are best seen when an examination is made of nations arranged in a northerly and southerly direction; the result is such as Human variawould ensue to an emigrant passing slowly along

tions.

a meridional track; but the case would be quite different if the movement were along a parallel of latitude. In this latter direction the variations of climate are far less marked, and depend much more on geographical than on astronomical causes. In emigrations of this kind there is never that rapid change of aspect. complexion, and intellectual power which must occur in the other. Thus, though the mean temperature of Europe increases from Poland to France, chiefly through the influence of the great Atlantic current transferring heat from the Gulf of Mexico and tropical ocean, that rise is far less than would be encountered on passing through the same distance to the south. By the arts of civilization man can much more easily avoid the difficulties arising from variations along a parallel of latitude than those upon a meridian, for the simple reason that in that case those variations are less.

But it is not only complexion, development of the brain. and, therefore, intellectual power, which are thus affected. With difference of climate there must be differences of manners and customs, that is, differences in the modes of civilization. These are facts which deserve our Their politimost serious attention, since such differences are cal result. inevitably connected with political results. If homogeneousness be an element of strength, an empire that lies east and west must be more powerful than one that lies north and south. I cannot but think that this was no inconsiderable cause of the greatness and permanence of Rome and that it lightened the task of the emperors, often hard enough, in government. There is a natural tendency to homogeneousness in the east and west direction, a tendency to diversity and antagonism in the north and south and hence it is that government under the latter circumstances will always demand the highest grade of statesmanship.

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