those above the firmament. And, in continuation, the residual waters were separated from the dry land, and the two unitedly stood forth, in pleasing variety, as a fitting pedestal for the plants and animals of the more recent world. Whilst the same principle seems to have been carried out even in the formation of these; for animal and vegetable organic forms, endowed with life and vegetable vitality, were separated from the more inert materials which constituted the terraqueous globe. In short, the great leading feature of the creation seems to have been SEPARATION. A separation between that which was, and which still continues to be, to a certain extent, under the influence of ATTRACTION or DARKNESS, and that which, by the immediate agency of the Creator, has been immutably placed also, in degree, under the dominion of LIGHT

or EXPANSION.

So far as has been revealed we are enabled to trace the extent of this principle of separation; how far it really extends, is not for us, as finite beings, to enquire. The veil which has been thrown over this subject we dare neither touch nor attempt to draw aside: our becoming position is reverential obeisance before it, and to His will who alone knoweth or can know, what might have been the consequences had He not stretched forth His hand "at the beginning," and overruled the influence of "the darkness which reigned upon the face of the universe!" This course, which fortunately puts all conjecture at an end, has been adopted; and our duty now, in place of seeking "to interfere in things which are too high for us," is to receive with reverence, thankfulness, and faith, the revelation which has been made to us respecting it; and, whenever in our power, to endeavour to apply the knowledge, which we have thus acquired, to the glory of the Creator.

SECTION VII.

METEOROLOGICAL PHENOMENA RESULTING FROM THE LIGHT, AND FROM THE EARTH'S PROTOROTATION.

CHAPTER XXIX.

The subject of the previous Chapter continued. Atmospheric phenomena. Scientific evidence of the manner in which the Aerial and the Aqueous portions of the Atmosphere respectively act under the influence of a common cause. Scriptural and philological confirmations of these announcements. Application of the information acquired from both of these branches, to the further elucidation of the Dynamical Theory.

FOLLOWING up the design, which we contemplated in the previous chapter, of preparing the mind for the investigations which we shall soon have to undertake in a subsequent part of this work, we shall now proceed to enquire into some of the other conditions of the atmosphere, namely, the manner in which the aerial and the vaporous portions conduct themselves under meteorological changes affecting them both. For this purpose let us refer to the eighty-eighth Theorem, which states, "That when a space is filled with a mixture of gas and vapour, these two bodies act, under changes of volume, in exactly the same manner as they would if each separately occupied the whole space; the gas dilates and contracts, changing its pressure and temperature with its density. The vapour obeys the same law, so long as no part of it is condensed into a liquid; but as compression renders condensation more easy by the more rapid development of heat, when much compression is used, a portion of that caloric necessary to maintain the vapour in the aeriform state will escape. A corresponding quantity of the vapour will become liquid; and the remainder will be mingled

with the gas, having the same tension which it would have if the gas were not present." And in connection with this, we shall again refer to a clause of the ninety-third Theorem, although it has been already recapitulated, "That whenever," by any meteorological cause," the temperature of the air is reduced below the limit at which the suspended vapour is maintained in a state of saturation, condensation takes place, and rain or aqueous clouds are produced."*

The following are some of the evidences, bearing upon those points which it may be satisfactory and interesting to peruse:

"Clouds," says Professor Whewell, "are produced by aqueous vapour, when it returns to the state of water. This process is condensation, the reverse of evaporation. When vapour exists in the atmosphere, if in any manner the temperature becomes lower than the constituent temperature requisite for the maintenance of the watery state, some of the steam will be condensed and will become water. It is in this manner that the curl of steam from the vent of a steam boiler becomes visible, being cooled down as it rushes into the air. The steam condenses into a fine watery powder, which is carried about by aerial currents. Clouds are of the same nature with such curls, the condensation being generally produced when air, charged with aqueous vapour, is mixed with a colder current, or has its temperature diminished in any other manner. Clouds produce rain. In the formation of a cloud the precipitation of moisture probably forms a fine watery powder, which remains suspended in the air in consequence of the minuteness of its particles; but if from any cause the precipitation is collected in larger portions and becomes drops, these descend by their weight and produce a shower."

At another part of his Treatise, when noticing the laws of electricity, he adds—

"We cannot trace very exactly the precise circumstances in the occurrences of the atmospheric regions, which depend on the influences of the laws of electricity; but we are tolerably certain, from what has been already noticed, that if these laws did not exist, or were very different from what they now are, the action of the clouds and winds, and the course of vegetation, would also be other than it now is. It is, therefore, at any rate very probable that electricity

* See also 94th Theorem and evidences.

has its appointed and important functions in the economy of the atmosphere, and this being so, we see a use in the thunder-storm and the stroke of the lightning. These violent events are, with regard to the elasticity of the atmosphere, what winds are with regard to heat and moisture. They restore the equilibrium where it has been disturbed, and carry the fluid from places where it is superfluous to others where it is deficient. In the natural world, these apparently destructive agents are, like all the other movements and appearances of the atmosphere, parts of a great scheme, of which every discoverable purpose is marked with beneficence as well as wisdom."

"When the air," says the author of the Philosophy of Storms,' near the surface of the earth becomes more heated, or more highly charged with aqueous vapour, which is only 5-8ths the specific gravity of atmospheric air, its equilibrium is unstable, and upmoving columns or streams will be formed. As these columns rise their upper parts will come under less pressure, and the air will therefore expand; as it expands, it will grow colder about one degree and a quarter for every hundred yards of its ascent, as is demonstrated on the nephelescope.

"The ascending columns will carry with them the aqueous vapour which they contain, and, if they rise high enough, the cold produced by expansion, in consequence of diminished pressure, will condense some of the vapour into cloud; for, it is known, that clouds are formed in the receiver of an air-pump when the air is suddenly withdrawn. The height to which the air will have to ascend before it be cold enough to form clouds is a variable quantity, depending on the number of degrees which the dew-point is below the temperature of the air. . . . And the difference between the dew-point and the temperature of the air in degrees is called the complement of the dew-point."+

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"Mists and clouds," says Mr. Hutchinson, seem to consist of a multitude of hollow vesicles or bladders, the coatings of which are inconceivably thin, and similar in structure to those usually blown from soapsuds. These vesicles vary in size, according to the measurement of de Saussure, from 2 to 20 of an English inch in diameter. This is farther proved by the circumstance of

* Bridgewater Treatise, pp. 85, 89, 111, 112. Introduction, pp. viii. lx.

their specific gravity being such, that they remain suspended in the air without any tendency to descend, and even on frequent occasions are seen to ascend; whereas, if they consisted of round drops, without any internal vacuity, their descent would be rapid.

"Clouds, in order to their suspension, must displace a weight of atmosphere equivalent to their own. The dissolution of clouds is effected in two ways, viz.-by falling in rain, or by evaporation and reconversion into invisible vapour.

"That the formation of clouds is a necessary antecedent to rain, is proven by the fact, that rain never falls unless the sky immediately vertical be obscured by clouds. But though clouds be essential to its production, they never produce it until they have acquired a considerable degree of density. But how does it come about that the aqueous vesicles lose their vesicular form, and descend to the earth in drops of rain? . Upon reflecting on the different degrees of rapidity with which rain falls at different times, and in different climates, I am disposed to think that the capacity of the atmosphere for suspending aqueous vesicles is limited, and varies with its temperature; and from the greater density of clouds in warm climates, as well as the greater amount of rain which falls from them in a given time, it seems probable that the capacity of the air for suspending vesicles, like its capacity for holding moisture in invisible solution, increases with its temperature. Provided other things be equally favourable, the annual amount of rain that falls, and the heaviness of the showers, are greatest at the equator, and diminish as we ascend towards either pole. While the rainy direction of winds, in all latitudes beyond the tropics, is when it blows in the lower half of the atmosphere from a warm towards a comparatively cold climate."

"When the air can no longer retain the moisture blended with its particles," observes Dr. Thomson," it descends in drops upon the earth, purifying the atmosphere through which they fall, and fertilizing the ground with refreshing rain. This, or melted snow, is the purest of natural waters, though, in consequence of its solvent power, it generally contains some extraneous ingredients. The amount of rain, or meteoric water, which falls upon the ground is greatest in the tropics, and decreases as we approach the poles.

* Principles of Meteorology, by G. Hutchinson, pp. 122, 152, 172, 196, 197, 321.