The objects of the universe, or the natural bodies which affect our senses, become known and to Is by their properties, some of which affect one of our senses, whilst others affect some other sense. Thus we perceive luminous bodies through our eyes, sound through our cars, heat or cold by the touch or feel, &c. Some of these properties are called general, like gravity and extension, because they belong to all bodies ; and others, like transparency and fluidity, are called partienlar, because they to certain bodies only. The better we become acquainted with the properties of natural bodies, the more extended the sphere of our powers and of our advantages becomes ; and it is for the discovery of these properties, either in simple or in compound bodies, that experimental inquiries are insti tuted.
In the acquirement of knowledge, the human being has no other assistance besides that of his senses. and of his reason ing faculty. By the first he observes and acquires ideas of self-evident propositions, or properties of natural ; such as the human mind cannot dissent from without manifest violence to its perceptions ; by the second he is led from one of these evident simple propositions, to another strictly depending upon the first, then to a third strictly depending upon the second, and so on, to the acquisition of some idea more complex, and less apparent at the first annunciation. The constant observation of philosophers, with Sir Isaac Newton at their head, and the dictates of plain reasoning, have furnished certain axioms and certain rules of philoso phizing, the propriety of which is too evident to be objected to.
The axioms of philosophy, or the axioms which have been deduced from common and constant experience, are so evi dent, and so generally known, that it will be sufficient to mention a few of them only.
I. Nothing has no property ;. hence :2. No substance, or nothing, can be produced from. nothing.
3. Matter cannot be annihilated, or reduced to nothing.
The propriety of the last axiom may perhaps not he readily admitted by certain persons ; observing that a great many things appear to be utterly destroyed by the action of fire; also that water may be caused to disappear by means of evaporation ; and so forth. But it must be that in these eases the substances are not annihilated ; they are only dispersed, or removed from one place to another, and by being divided into particles very minute, they elude our senses, and escape our immediate notice. Thus, when a
piece of wood is placed upon the fire, the greatest part of it disappears, and a few a.hes only remain, the weight and bulk of which do not amount to the hundredth•part of the weight and bulk of the original piece of wood. In this case the piece of wood is divided into its constituent principles, which tame action of the fire drives different ways. The fluid part, for instance, becomes steam, the light coaly part either adheres to the chimney, or is dispersed the air. &c., so that if, after the combustion, the scattered materials were collected, (which may in a great measure be accomplbdied.) the sum of their weights would equal the weight of the original piece of wood.
4. Every effect has, or is produced by, an adequate cause, and is proportionate to it.
It may, in general, be observed, with respect to these axioms, that we only mean to assert what has been constantly shown, and confirmed by experience, and is not contradicted, either by reasoning, or by any known experiment. But we do not mean to assert that they are as evident as the axioms of geometry ; nor do we in the least presume to prescribe limits to the agency of the Almighty Creator of every thing, whose power and whose ends are too fin- removed from the reach of our finite understandings.
thus stated the principal axioms of philosophy, it is in the next place necessary to mention the rules of phi losophizing, which have been formed, after mature consi deration, fin• the purpose of preventing errors as Inuch as possible, and of leading the student of nature, along the shortest and safest path, to the attainment of true and knowledge. These rules !nay be reduced to four, viz.
I. We are to admit no more causes of natural things, than such as are both true, and sufficient to explain the appearances.
2. Therefore, to the same natural effects we must, as far as possible, assign the same causes.
3. Such qualities of bodies as are not capable of increase, or of decrease, and which are found to belong to all bodies within the reach of our experience, are to be esteemed the universal qualities of all bodies whatsoever.
4. In experimental philosophy we are to look upon propo sitions collected by general induction from phenomena, as accurately, or very nearly true, notwithstanding any contrary hypothesis that may be imagined, till such time as other phe nomena occur, by which they may either be corrected, or may be shown to be liable to exceptions.