INTRODUCTION TO CHEMISTRY.

I. MATTER AND FORCE.

§ 1. EXPERIENCE, or the repeated evidence of our senses, and the irresistible persuasion of the mind that "like causes will ever produce like effects," constitute the sound foundation of natural knowledge*.

The convictions arising from these impressions have directed the intellect of man, in all ages and in all stations, to control the powers which have been imparted to the material universe to his own advantage; the maintenance of a bare existence in savage life being dependant upon them no less than the polished arts of civilized society. It is strange, however, to remark how long a time elapsed, even in a state of high intellectual culture, before it was discovered that the same principles which teach the mere child that fire will burn, that water will flow, and that a moving stone will inflict a blow, and to guide his conduct accordingly, would lead to that higher acquaintance with the powers of nature, which we distinguish by the title of natural philosophy. The powers of reason had been exercised with success upon abstract science for ages before the voice of Bacon proclaimed, and insisted earnestly upon, the advantages of extending experience by experiment, and of adopting the accurate observation of phenomena, as the only safe guide in physical investigations; but from the moment that this course entered upon by the patient student of nature, natural science

was

Some eminent philosophers, however, maintain that the whole of our knowledge is not a mere collection of deductions from experience, but that there are ideas of which the mind has a perception, and propositions of which we have a conviction, antecedent to experience; that there are certain general and universal propositions in science of which we have an innate conception. But it has been well observed, that this opposition of views, after all, may be only apparent; for whether certain truths have been originally impressed upon our intellectual being, capable of being called forth by circumstances, or whether our minds have been originally so constructed as to be most permanently struck by those analogies amongst natural things which are really dependent upon their nature, as that nature is known to their Creator, the mind of man, on either view of the subject, is represented as in harmony with universal nature, and therefore capable of attaining real knowledge.

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has advanced with a constantly accelerating progress, extending the power of mind over the forces pertaining to matter in a corresponding degree.

It deeply concerns the student who proposes to himself to enter upon any branch of such investigations, that he should have a right perception of these truths; that he should correctly distinguish the difference between abstract and natural science, and clearly perceive the road along which his course must tend.

The contrast of these two great divisions of science has been forcibly represented by one of the living masters of both. "A clever man," Sir John Herschel has observed*, "shut up alone, and allowed unlimited time, might reason out for himself all the truths of mathematics, by proceeding from those simple notions of space, and number, of which he cannot divest himself, without ceasing to think; but he could never tell, by any effort of reasoning, what would become of a lump of sugar, if immersed in water; or what impression would be produced on the eye by mixing the colours yellow and blue."

§ 2. Experience, then, must be his guide; not the mere passive experience of observation, but the active experience of experiment: that is, he must not only carefully observe phenomena as they spontaneously present themselves to him in the ordinary course of nature, but he must purposely contrive and vary circumstances, in order that he may observe them.

To personal experience he must also add the well-attested experience of others; and the experience of past ages, as well as of the present; and as by following this course the generality of mankind attain to such an acquaintance with the properties of matter as ensures their comfortable existence, with which sensual object they are content; so he has but to persevere in the same, and it will lead him to that intimate knowledge of the order of creation, which constitutes science, and which is an object of ambition worthy of a rational creature.

The immediate wants of their nature early taught the human race to direct the agency of heat to their supply; and the accumulated experience of ages, widely diffused, has given the most unreflecting a command over that principle which strongly contrasts with the general ignorance concerning the no less general and powerful principle of electricity, the very existence of which could scarcely be said to have been recognised till within the * HERSCHEL'S Discourse on Natural Philosophy, p. 76.