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 When it is withdrawn from fluids, in general they congeal.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 by the Hand of unerring skill, would be of no use.

chaos would it be!

* 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.

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.

HOW ATMOSPHERIC HEAT IS PRODUCED.

removed from the surface of the earth, the colder we find it.

This fact seems to countenance a recent and ingenious conjecture, that caloric, or the matter of heat, is not transmitted from the sun; but that it is a subtile fluid originally belonging to our earth. The author of this hypothesis supposes that the sun is the great agent in the production of heat, without imagining it a vast globe of fire. He represents the sun as a great store-house of light,—a power indeed the most active in nature, but no ways destructive. He thinks that light produces heat merely by exciting an insensible action between caloric and the particles of matter contained in bodies; and this system is more analagous to the general principles on which our globe is constructed, than that which is generally embraced, and enables us to solve the great difficulty concerning the distribution of heat among the different planetary bodies; for, according to this view, those nearest the sun may have no more than those at the most remote distance. We have only to suppose, says he, the quantity of caloric to be proportioned to the distance; and if a small quantity exists in the planet Mercury, no more heat may be excited than is done by a larger quantity in Saturn. To intimate the glory of his own infinite essence, Jehovah represents himself to us under the metaphor

NATURE OF THE ELECTRIC FLUID.

of Light. "God is light, and in him is no darkness at all." The adorable Redeemer speaks of himself as being "the light of the world:" and affirms, that "those who follow him shall not walk in darkness, but shall have the light of life." By the glory of his person, the brightness of his example, and the divinity of his instructions, he diffuses moral and spiritual light over a dark world. He is that to his church, which the sun is to our system-the source of all spiritual light, joy, and prosperity. He is a "light to lighten the Gentiles, and the glory of his people Israel."

There is another fluid in combination with this atmosphere, which we must not forget to mention It is ELECTRICITY. Indeed, whether this be another fluid, essentially distinct from that of solar light and fire, is not yet determined. In many particulars they agree, and in some they differ*. Whether it be the same fluid or not, this is certain, that it is every where diffused through our atmosphere, and is employed by the Hand of infinite power and intelligence, to effect many of the wonders of nature. It is a most powerful stimulant, and acts as such on both animal and vegetable organization. Linnæus, with Sir Isaac Newton, and some other eminent philo

* See this subject discussed in the Encyclopædia BritannicaElectricity; and the reasons on both sides stated in Gregory's Economy of Nature, 3d edit. Vol. I. p. 312-315.

USES OF THE ELECTRIC FLUID.

sophers, consider it the medium; in the hand of Providence, of communicating life and energy to the whole animal frame, by means of the nervous system, on which it acts with remarkable facility. The nervous system is certainly much affected by electricity; and consequently, the muscular. As by it a considerable number of diseases are cured, so it is by no means unphilosophical to infer, that by it many diseases are prevented. It is found to be particularly serviceable in promoting the growth of plants: for plants which are placed adjacent to an electrical apparatus which is often used, grow much more rapidly than they do otherwise. And perhaps rain proves more fertilizing than other water, because, descending through the atmosphere, which is always possessed of a considerable portion of this fluid, it may be electrified, and every drop carry some of it to the earth.

In the common operations of nature, the equilibrium is preserved, and the presence of the electrical fluid is not perceived; but when by any cause that equilibrium is destroyed, its awful powers appear in vivid lightnings, the roar of thunder, the rending of trees, the destruction of houses and their astonished inhabitants. The Aurora Borealis, as well as thunder and lightning, and various other meteorological phænomena, show the presence and importance of this fluid in some of the grandest operations of nature, which may be explained by a knowledge of its