Imágenes de páginas

stomach, and the trachea is the tube through which the air passes into the lungs; a small valve at its superior orifice, whilst it admits the passage of air, prevents that of any other fluid or substance, which, by its irritation in the lungs and air-vessels, would be the occasion of fatal consequences. There is a valve also placed in that orifice of the stomach which enters the intestines; it opens to suffer the food to pass, but prevents its returning.

Within the cranium or skull is situated the brain, enveloped in a very fine membrane full of blood-vessels, and called pia mater; a second membrane, much thicker and stronger, adheres to the internal surface of the cranium; and between these is a third mem. brane, so very delicate and transparent, as to be scarcely perceptible. Besides these parts, each of which has a determinate place, there are others which are dispersed over the whole body, such as bones, ar. teries, veins, lymphatic vessels, muscles, and nerves. The bones are united together by joints, and serve to support the body, to render it capable of motion, and to preserve and protect the softer parts. Veins and arteries circulate the life-sustaining blood throughout the body. The nerves, of which ten principal pair are enumerated, are small white cords; they proceed from the brain, are distributed to every part of the body, and are the organs of sensation and motion. The whole body is full of pores so small as to be imperceptible to the naked eye; and through these is continually exuding a subtle matter called the insensible perspiration. No less wisdom is manifested in the fluid than in the solid parts of the body. The blood, chyle, lymph, bile, marrow, and the different kinds of viscous and glutinous humours secreted by various glands; their different properties, their desti nation, effects, and the manner in which they are se parated and prepared; their circulation and renova

[blocks in formation]

tion; all bespeak the most astonishing art and the profounded wisdom.

Let us now recapitulate all the excellencies of our structure. The bones, by their solidity and their joints, form the foundation of this beautiful superstruc ture; the ligaments are tendinous cords, which unite different parts together: the muscles are fleshy substances, which perform their functions like elastic springs; the nerves, which extend to the most distant parts of the body, communicate the power of sensation, and enable the different organs to perform their functions; whilst the arteries, and veins, like inexhausti ble rivulets, pour the life-streams to every part. The centre of circulation is the heart, from and to which all the blood proceeds; and respiration is performed by means of the lungs. The stomach and intestines are the organs where the food undergoes those changes which are necessary for the support of life. The brain is the common centre from which the nerves proceed to communicate sensation to the body, and enable the senses to receive the impressions which they convey to

the soul.

Adorable Creator! how wonderfully has thou found us! Though the heavens, which so magnificently display the glory, were not to exist, though I was the only being upon the face of the earth, the admirable structure of my body alone would suffice to assure me of the immensity of the power, and convince me of thy immeasurable wisdom; Let us then, as often as we meditate upon this wonderful organization of our bodies, praise Him who has so formed us, and offer up our thanksgiving for his manifest goodness.


FROM the numerous experiments which have been made upon the subject of electricity, no one can

doubt the existence of a matter which, from its singu. lar effects, has excited the attention of Europe for more than half a century. It appears that this fluid is equally diffused though all bodies, but is so extremely subtle that we cannot perceive it, and we only know it to be present from the effects it produces; when put in motion it rushes from one part to another to restore the interrupted equilibrium. It is necessary to distinguish two kinds of electric bodies; those in which the electric fluid may be excited by means of friction, and those which receive their electric power by com. munication with the former. The principal substances which compose the first class, are, glass, pitch, resin, sealing-wax, hair, silks, and air; to the second class belong water, metals, &c. Bodies of the first kind may be made capable of perserving the electric matter collected in them, whilst those of the second class lose it as soon as they receive it*. Machines have been invented, in which, by means of a wheel, a rapid rotation is given to a glass globe, or cylinder, upon which is placed a cushion of silk, against which, whilst whirling round, it rubs. By this friction the globe preserves its electric virtue, which may be extended to any distance by means of metallic bars, or chains which communicate with the glass. If, while the machine is working, we touch the chain, we immediately receive a shock; and, if the room is darkened, a luminous spark will be perceived. Let any number of persons

*Those substances mentioned in the first class, to which may be added diamonds, balsamic and bituminous bodies, as amber, sulphur, &c. the coverings of animals, as feathers, wool, bristles, silk, vitrified bodies, and all substances that, when rubbed, attract light bodies, are called electrics or non-conductors. Those on the contrary in which, when friction is employed, the electric fluid is not excited or put in motion, are called conductors or non-electrics; and they consist chiefly of metals, minerals, aqueous and spirituous liquids, living creatures, and animal and vegetable substances, as trees, plants, bones, shells, &c.

[ocr errors]
[blocks in formation]

join hands and form a circle, and by means of the chain make a communication with the machine; and they will all receive a shock at the same time, which may be more or less violent. The electric fluid may be accumulated to such a degree as to kill by its discharge the largest animals.

This experiment is performed with several glass jars nearly filled with water, and which, connected together by chains, communicate with the glass globe before described. The water communicates to the internal surface of the jars a great quantity of electric matter, their external surface at the same time losing an equal quantity by means of its communication with some conducting body. A vivid flash, loud explosion, and a violent agitation, ignition of combustible mat ter, and the death of the subject of the experiment, are the consequences of this experiment.

There are other effects which are common to all experiments of this kind; such as a sulphureous smell, an agitation in the air, a sudden flash, and the electric matter acquiring a new property. Some experiments have failed because the metallic rods which served as conductors were too angular and pointed. It has been suspected that the electric fluid in such cases was dissipated by means of the points; and this was confirmed when on approaching the face or hand to the point of the rod, a copious stream of electric fluid emanated from them; it was also conjectured, that these points which throw off the electric fluid might attract it, and a number of experiments have since established it as a truth.

Electricity has been applied by physicians in many complaints with great success; and a still greater ad. vantage which we derive from its investigation, is the analogy which naturalists have discovered between e. lectricity and lightning, which has given rise to new conjectures upon the nature of thunder; and has taught

́us to secure our buildings, by means of metallic rods, from the destruction they often suffer during a storm.

Thus we are continually receiving new solutions of the mysteries contained in the great works of nature; and from the success of these investigations we should be excited to more industry, and to pay greater attention to the works of the creation daily offered to our view.


Manner in which Thunder is formed.

FORMERLY, and even to the beginning of the eighteenth century, it was commonly supposed that thunder was occasioned by the agitation of saline, sulphureous, and other substances contained in the air. It was imagined that there was the greatest resemblance between the effect of fire-arms and that of thunder and lightning. But all the means by which men endeavoured to explain and establish this system, were not sufficient to do away the difficulties that presented them. selves, nor to account for the fact. Since that period, however, the phenomena produced by the electric fluid have been more attentively observed, and a very different cause has been assigned to the formation of thunder. The great resemblance between it and electricity has convinced naturalists that they are produced by the same causes, and that electricity is in our hands what thunder is in nature. It will not be difficult to demonstrate this, even to those who are ignorant of natural philosophy, if they will only take the trouble to compare the effects of thunder with those of electricity.

The effects of thunder are known by peals heard at a greater or less distance, and by flashes of fire; buildings struck by it are often consumed by flames;

« AnteriorContinuar »