Imágenes de páginas

external cause. If a child secretes a sweetmeat in a hiding place for a time, and afterwards, on looking for it, finds that it is not there; the infant is instantly conscious that it has been removed by some adequate power, and, if on making enquiry respecting it, the answer was given that nothing had removed it, the assertion would be deemed absurdly untrue, which shews that the child is conscious that no change can take place, without the agency of an adequate cause, or in other words, that every change is an effect.

Now, if the susceptibility to consciousness did not make the child aware of this fact, that every change is an effect, no experience could; for it is a universal truth, and experience can only teach individual facts; thus, if the child had seen its sweetmeats taken away three times, these occurrences would shew that three times a change had taken place, by the agency of a cause, but this would not authorize the conclusion that all changes take place by the instrumentality of causes; besides, mere experience would have impressed a contrary conviction on the child; for the majority of changes that take place around it, arise from causes unseen and unknown, and consequently, if the child were left to the guidance of mere experience, they would impress upon it the notion that change often takes place without any cause, while the fact is, that when a change takes place, though the cause be unseen, still with the consciousness of the change, is the knowledge that it has a cause; indeed, it is impossible for a human being to conceive the notion of a change taking place, without an adequate


The next fact is, that we are conscious that similar causes produce similar effects, which implies that similar effects are produced by similar causes. This, in plain language, merely signifies that similar things are similar, which is a truism. If we take a substance, and throw it into the fire, and observe that the fire burns it, afterwards on doing the same with what appears a similar substance, we expect it also to be burnt, but if it be not so, we are conscious that the substances are not


alike in this respect, however they may resemble one another in some things. The strong resemblance of two things may lead us to suppose them similar in all their abilities, but if on experiment we find that they are not so, we of course are conscious they are not similar things. If a stranger to electricity were to see the flashes of lightning coming from a prime conductor, he might at first suppose it to be fire, but on going near and finding that it did not heat or burn him, he would at once be conscious that it was not fire; for to be such, it must be able to heat and burn him, and without this ability it is not fire. That which excites through the medium of his eyes, the consciousness of a bright blazing figure at a certain distance from him; which excites through the medium of his skin, the cousciousness of heat, and which on putting his finger to it, commenced the painful decomposing process of burning him, he knows to be fire; but, if it be deficient of any one of these abilities, it is dissimilar from fire, and cannot be considered as such. Of course I do not mean when I use the phrase similar things an exact similitude in shape and intensity of ability, for fire is still fire whatever figure it assumes; whatever intensity of brightness, or heat it may display. All then that is meant by saying that two things are similar, is that they are possessed of similar specific properties, however these properties or abilities


be modified. All that we can know of things, are the abilities and susceptibilities of which they are possessed; these form their characteristics, by which they are distinguished from one another, or assimilated. A cannon ball has a certain set of characteristics, it excites a consciousness of a round metallic figure possessed of much weight. Water excites a consciousness of itself in the brain, and our knowledge of it consists of certain facts respecting its appearance to the eye, the sensation of touch which it has the ability of exciting, together with various other characteristics. Now if the solid iron ball be placed in the water, it sinks, and we are made aware that it is possessed of greater ponderosity than water; this then forms one of its distinguishing characteristics; and if afterwards we saw a similar looking ball flung into what appeared to be water, and instead of sinking it swam on the surface, we would at once be made conscious, that either that which appeared to be water was not water, or, that which appeared to be a solid iron ball was not such. We would at once perceive that the fluid was possessed of greater weight than iron, or else either that the ball was not a solid one, or if so, was made not of iron, but of a substance lighter than water. Water is possessed of certain characteristics, one of which is its specific gravity; iron has its characteristics, one of which is its specific gravity; and a triangle is possessed of its characteristics, such as its lines and angles; and the relative gravities are just as essential to the former, as the three angles are to the last mentioned. Any thing to be similar to any one of them has the ability to excite the consciousness of the characteristics of the thing, and to be different, it is possessed of different abilities. This is mere truism, but of much practical importance, as will be seen in the sequel.

Consciousness of external things is excited in the brain through the medium of different nervous organs called senses. The skin not only covers the outside of the body, but also the inside of the mouth, nose, windpipe, lungs, gullet, stomach, duodenum, intestines, &c.; and the nerves in it are instruments for the production of various kinds of consciousness. Bodies coming in contact with any part of the outer skin, the skin of the mouth, or that of the inside of the nose, make us conscious of themselves by causing a sensation in the part; these sensations have different names according to their locality, and the nature of that which is the external causes of them; particles of perfume inhaled through the nose, excite in the brain the knowledge of a sensation of smell existing in the nose, and different things placed in the mouth make us aware of numerous tastes. It has before been explained that whenever a sensation is excited, the consciousness of the change that takes place from its nonentity to its existence includes in itself the know

ledge that such change is effected by something; and by this principle we gain a knowledge of those things which act on our nerves. The sensation all through its continuance, is known to be produced, and the consciousness includes the knowledge both of the sensation and the ability of that which produces it. Now the sensation and the ability of that which excites it are so associated together, that in most languages they have received the same name, smell not only signifies the sensation, but also the fragrant particles which produce it, thus we say the smell of flowers is on the breeze, alluding to the particles of floral perfume; or we speak of the actual sensation called smell existing in the nostrils. In the same way taste refers sometimes to our sensation, and at others to the abilities of different meats to excite it, the former is said to be located in our mouths, the latter in substances external to us; we often hear men say they have a pleasant or disagreeable taste in their mouths, and as frequently that certain meats have peculiar tastes.

There are four kinds of organs; the nerves, in which are susceptible of being acted on, so as to produce feeling and thought, by the things by which the animal is surrounded; these organs are 1st, The Skin ; 2nd, The Muscles ; 3rd, The Ears; 4th, The Eyes. There are several kinds of sensation produced in the skin, but as two of them are appropriated to localities they are considered as distinct; these two are taste and smell: taste is excited in the skin of the tongue, smell in that of the

Touch is a sensation common to all parts of the skin, but more particularly acute at the points of the fingers. Through these senses are excited thoughts of the roughness, smoothness, heat, coldness, sweetness, bitterness, saltness, sourness, fragrance, &c., of things by the action of the things on these senses.

The muscles are acted on by the thoughts and feelings, when they determine on certain motions. The motion of and the degree of resistance given to the muscle, excite feelings in it. These sensations have been erroneously classed with those of the skin, from their being


intimately associated with them. Thoughts of weight, hardness, softness, bodily motion, &c., are excited by the action of things on the muscles ; when we move our hand against an object and find the sensation of resistance excited in the acting muscles, we call the object hard, as for instance, a wall; when the hand is pressed against an object such as a pillow, and but little resistance is given to the muscle, the object is called soft. In our bodily motions, efforts are made to overcome the power of gravitation, and this power thus acting on the animal frame, excites feelings relative to motion. The heaviness or lightness of any thing is known by the sensation of difficulty or ease which it produces in the muscle during the effort to lift it.

In the auditory nerve of animals is excited the sensation of sound, by the vibration of the atmospheric medium: a bell is struck with a hammer, it vibrates, and the vibratory motion is communicated to the air, and by it through the ears to the auditory nerves of those within hearing distance, and immediately they have a sensation of sound excited, or in other words, they hear the bell.

When an object is placed before a camera obscura, by the agency of the rays of light, an image of the object is depicted in it; so, in the eye which is similar to the camera obscura, the light passing from objects, depicts their images on the retina, which is an outspread part of the optic nerve: thus are excited sensations of colour and visible shape, which latter consists of the length, breadth, and linear appearances of things possessing visible abilities : matter such as atmospheric air not having ability to excite vision, is of course unseen.

The principal facts connected with the sensations of seeing and hearing form the two important sciences, optics and accoustics, neither of which come within the sphere of the present enquiry, however closely they may be connected to it. These sensations differ from the others that I have considered, inasmuch as they are excited by things, not in contact or close proximity with

« AnteriorContinuar »