air is ready to come forth spontaneously. In this circumstance, should the temperature of the air sink a very few degrees, rain will inevitably fall. To what extent, however, it is more difficult to determine; for we often observe the air pouring down a heavy shower one moment, and so dry as to absorb moisture the next.

The earth is thus surrounded with two distinct atmospheres, mechanically mixed. The vapour or condensable elastic fluid, struggles to rise in a medium, whose heat decreases by expansion, at a much more rapid rate than its own; whence it is condensed in vesicular strata in the upper regions. Its latent heat is disengaged in the condensation, and imparted to the air; thus tending to temper the inequalities of the medium in which it moves, and to constrain it to its own law. This process must evidently disturb the equilibrium of the aerial fluid, by modifying its temperature and density. The system of atmospheric currents is also affected by the unequal expansion. The air at the surface of the globe is usually far from the term of aqueous saturation, in consequence of the condensing influence of the cold strata above. Thus the current of vapour which is constantly moving from the hotter to the colder regions, may pass from the equator to the poles, without producing that condensation in mass, which would otherwise have clouded the whole depth of the atmosphere, with precipitating moisture. The clouds are thereby confined to parallel and nearly horizontal planes, with intervening clear spaces. The mechanical influence of each fluid being proportional to

ATMOSPHERE OF THE PRIMEVAL GLOBE. 69

its elasticity, that of vapour compared with air, can never at most exceed the ratio of 1 to 30; so that the general character of the mixed atmosphere, is derived from the permanently elastic constituent. This controls and distributes the other by its movements. An important re-action, however, takes place. By gradual, but almost insensible expansions, the equipoised strata of the atmosphere are disturbed, storms arise, which agitate the mighty ocean, and prevent that stagnation of air and water, which would prove injurious to organic beings. But the disturbing forces contain the elements of counteraction; and the tempest soon exhausts its resources, and leads in a calm.-Daniell's Essays.

Thus we perceive, that the mechanism ordained by INFINITE WISDOM, " to divide the waters which are under the firmament, from the waters which are above the firmament," is inferior to none of those refined and beautiful adaptations which lie most obvious to human sight, in the kingdoms of life, or in the starry heavens. But for this delicate adjustment of conflicting elements, the clouds and concrete vapours would have obscured the sky, to an indefinite distance, concealing for ever the glorious orbs which circulate in celestial space.

On a subject so transcendent and mysterious as the state of the new born atmosphere, it becomes not man to dogmatise. It is, therefore, in perfect humility, that I offer the following suggestions. No cause hitherto operated, that we can assign, why the sub-aqueous globe should possess any dif ference of temperature at its equator and poles. Even those who believe that the creation of light,

implies the creation of the sun, suppose that his beams could not penetrate to the terrestrial sphere on account of the dense vapours which still involved it. Mr. Daniell, in his 35th table, represents very faithfully, I believe, the condition of an atmosphere of air, to which vapour was admitted from a sphere of equal temperature covered with water. "A perpetual struggle," says he, "would ensue between the temperature due to the density of the air, and the constituent temperature of the vapour, accompanied by perpetual evaporation below, and simultaneous condensation above. No winds or lateral currents would be established, but an increasing circulation in a vertical direction."

On the gathering of the waters into one place, and the appearance of the dry land, the cause of the universal cloud which veiled nature being removed, its face should have been now cheered partially at least, with the sun's beam, had his orb been invested with luminiferous influence. But it was not so for another day elapsed, before the Sun, Moon, and Stars, were set as lights in the firmament.

We cannot conclude this chapter, without adverting again to the philosophical precision with which Moses has defined the main function of the firmament to separate the waters from the waters; ages before Philosophers had any idea of the mechanism of clouds. This has at length been happily developed by Mr. Daniell.

SEPARATION OF LAND AND WATER.

71

CHAP. IV.-PRIMEVAL LAND AND OCEAN.

pro

CIRCUMSTANCES which will transpire in the progress of our researches, cause me to assign a different portion between the dry and humid surface in the Primeval Globe, from that which now prevails. I am led to conclude, that the area of the land bore to that of the water, probably the ratio of equality, instead of nearly 100 to 365, as at present. One obvious consequence of this condition was, that the depth of the Primeval ocean was greater, as its superficial expanse was less. By this means, the water came into far deeper and more extensive contact with those ignited, combustible, and explosive materials, which the phenomena of mines and volcanoes, demonstrate to exist within the crust of the globe.

We learn from Physical Astronomy, that the only form compatible with an universal diffusion of waters round a revolving globe, is an oblate spheroid of certain dimensions. To the equilibrium of a fluid mass, thus diffused, it is necessary that any two columns reaching to the surface from any point within the fluid, should balance one another, or should press equally on that point. This equilibrium of the columns will take place in a mass of homogeneous fluid revolving round an axis, if it be formed into an oblate spheroid, such that the polar semi-axis is to the radius of the equator, as the attraction at the equator diminished by the centrifugal force at the same place, to the attraction at

the pole.* A homogeneous fluid of the same mean density with the earth, and revolving on an axis in the space of 23 hours 56' 4" of solar time, as it does, would be in equilibrio, if it had the figure of an oblate spheroid, of which the polar axis was to the equatorial diameter as 229 to 230. This is accordingly the figure which Newton gives to the earth. Est igitur diameter terræ secundum equatorem, ad ipsius diametrum per polos, ut 230 ad 229, Prin. L. iii. prop. 19. But if the mass, supposed to revolve on its axis, be not homogeneous, but be composed of strata that increase in density towards the centre ; the figure of equilibrium will still be an elliptic spheroid, but of less oblateness, (less compressed at the poles,) than if it were homogeneous. This is the predicament more nearly of the earth, whose ellipticity is about 1.

But there are actually considerable irregularities on the surface of the earth, so that the spheroid which agrees best with the degrees measured in France, is one having an ellipticity of; nearly double of what may be accounted the mean ellipticity. These irregularities of shape consist in an unequal magnitude and density, of the great mountain masses and table lands, now standing above the

waters.

But the form of the terrestrial ball was the regular spheroid, while it lay enveloped in the shoreless deep. "And GoD said, Let the waters under the heaven be gathered unto one place,

* Maclaurin’s Fluxions, Vol. II. ý 636–641,