WATER RAISED-CLOUDS FORMED.

is vast beyond what most people suppose. Every ten square inches of surface of water, yields in vapour, every twenty-four hours, a cubic inch of water; and each square foot, half a wine pint; every space of four feet square, a gallon; a mile square, six thousand nine hundred and fourteen tuns; and a square degree of sixty-nine English miles will evaporate thirty-three millions of tuns a day; and the whole Mediterranean, computed to contain one hundred and sixty square degrees, at least five thousand two hundred and eighty millions of tuns each day. P

Clouds are formed probably of vast numbers of spherules, or small globes of water filled with air, which, being heated by the sun, become specifically lighter than the lower stratum of the atmosphere; and consequently, like so many balloons, ascend till they arrive at the same temperature of air with their own in rarity. Being collected together, these spherules form clouds, which float along the denser stratum of air, till being pressed together, they form drops of water, which become again specifically heavier than the air which supports them, and consequently descend in gentle showers upon the earth. So that air contributes to the formation of clouds, the support and conveyance of them to different parts of the earth where the God of Providence sees them wanted, and forms a medium to prevent the water from

P Philosophical Transactions.

ATMOSPHERIC PRESSURE.

rushing down in torrents, and to make it distil gently upon the tender herb.

Besides these, air is subservient to various other

important purposes :-by refracting the rays of light,

it diffuses them more widely over the earth; it supports combustion; when agitated into winds, it aids the interests of commerce, and a variety of necessary arts of civilized society. Its separate properties act independently of the rest in various cases. Its pressure raises water in the pump. It is owing to this pressure, that water is retained in its liquid and useful state; not frozen; neither vapour :-were it not for this pressure, as soon as ice has imbibed heat enough to melt it, evaporation would immediately raise it into the atmosphere, where it would be retained, and dissipated in the higher regions.-Were it not for this pressure of the atmosphere constringing the vessels in animals and vegetables, the elastic fluids contained in the finer vessels would inevitably burst them, and life would become extinct."

By being rarefied in the lungs of animals, and expelled unfit for respiration, air ascends through the denser medium of the wholesome atmosphere, and no longer annoys the animal. Were it not possessed of this property, it would form itself about their mouths

It has been calculated that the weight of air, which presses upon the whole surface of the earth, is equal to that of a globe of lead sixty miles in diameter.

NATURE OF LIGHT AND HEAT.

a poisonous atmosphere, and must immediately prove destructive. Air constitutes the medium of sounds, which, without it, could not be heard; and consequently, two of the noblest organs of the human economy, the organ of speech and that of hearing, would at once be rendered useless, and society lose some of its principal endearments.-What a vast variety of purposes were to be accomplished by this one element! and the more we examine its nature, the more we are convinced of its suitableness to these ends. This is wisdom!

It has been ascertained by experiment, that no other gaseous body, with which we are acquainted, can be substituted for atmospheric air. All the other gases have been tried, but they all prove fatal to the animal which is made to breathe them."

LIGHT and HEAT are those important fluids employed by the God of Nature to aid in carrying on the curious operations of vegetable and animal life. On the real nature and causes of these fluids, it becomes me to be silent, since the greatest philosophers that ever existed have differed very widely in opinion, and remain yet at variance: however, all agree that they are matter in a fluid state, and the most subtile of all those fluids with which we are acquainted. Whether light be the same thing as heat, is not yet determined :-however, this seems to

Dr. Thomson.

IMPORTANCE OF LIGHT AND HEAT.

be agreed upon, that light is always accompanied by heat. If they be different modifications of the same body, they act separately under those different modifications; for the one is often found carrying on its operations, where the other is not perceived. Heat naturally tends to separate the particles of most substances, and is, no doubt, one of the grand agents in promoting the digestion of food in the stomachs of animals. When it is withdrawn from fluids, in general they congeal, It is essential to vegetation; for, without it, seeds will not germinate, plants cannot grow, neither can animals. It blends itself with all substances in this system. However close their texture may be, and impervious to other bodies, heat enters into their pores with facility, and knows no obstruction.

LIGHT, as such, is also of indispensable importance in this world. Without light, what a horrid The eye, so curiously fashioned

chaos would it be!

by the Hand of unerring skill, would be of no use.

The intensity of light and heat is inversely as the squares of the distances from the body from which they proceed. For instance,---at one foot, the intensity is one degree; at two, the intensity is four times less; at three, the intensity is nine times less; at four, sixteen, &c.

t

It is worthy of remark, as it tends to discover the goodness of God, that the use of fire is entrusted exclusively to man. Most other creatures have a natural dread of it, and flee from it. Were it at the control of the brute creation, what dreadful havock would they make!

VELOCITY OF LIGHT-NATURE OF THE SUN.

This organ is made for the purpose of vision; and light is created to perfect the design: the one is exactly adapted to the other. Solar light is of essential importance to the perfection of vegetation. Without it, vegetables may grow, but they are destitute of their beautiful colours, and their fragrant odours. It is light which paints the lively green on the leaf; the red, the blue, the purple, and the unnumbered beauties on the flower.

The velocity with which light passes from a luminous body is almost inconceivable". It completes a distance of one hundred and sixty thousand miles in one second of time. The rays of light flowing from the sun, fall upon our atmosphere, (as before mentioned) when they are refracted and reflected in all directions, and cover at once one half of this globe with their splendour, diffusing, wherever they come, life and gladness.

The air does not appear to be heated by the rays of the sun passing through it; but when they meet with an opaque body like the earth, heat is produced, and diffused through the surrounding atmosphere. This accounts for the fact, that the further we are

" Dr. Herschel imagines that the sun is an opaque body, probably an habitable world; and that the light and heat, which we receive from it, are owing to an atmosphere which it has of elastic fluids, of a phosphorescent nature, by the decomposition of which light and heat are evolved. He also thinks that light and heat are distinct fluids.