adapted to particular ends. The subject is one of great and extensive importance, but it appears desirable that the name were altered, though it is sanctioned by high authority; for, when viewed in connexion with the sense in which the word cause is employed in modern science, it expresses a meaning remarkably different. The investigation to which it refers is also of a distinct nature, though one of the highest interest. It leads us chiefly to the inductions of natural religion respecting a great and intelligent First Cause; but it may also be directed to the discovery of truth in regard to the phenomena of nature. One of the most remarkable examples of this last application of it is to be found in the manner in which Harvey was led to the discovery of the circulation of the blood, by observing the valves in the veins, and contemplating the uses to which that peculiar structure might be adapted.

The object of all science is to ascertain these established relations of things, or the tendency of certain events to be uniformly followed by certain other events; in other words, the aptitude of certain bodies to produce or to be followed by certain changes in other bodies in particular circumstances. The object of art is to avail ourselves of the knowledge thus acquired, by bringing bodies into such circumstances as are calculated to lead to those actions upon each other of which we have ascertained them to be capable. Art, therefore, or the production of certain results by the action of bodies upon each other, must be founded upon science, or a knowledge of their fixed and uniform relations and tendencies. This principle applies to all sciences, and to the arts or practical rules which are founded upon them; and the various sciences differ only in the particular substances or events which are their more immediate objects.

In the physical sciences, we investigate the rela

tions of material substances, and their actions upon each other, either of a mechanical or chymical nature. On the relations thus ascertained are founded the mechanical and chymical arts, in which we produce certain results by bringing bodies into such circumstances as are calculated to give rise to their peculiar actions. But mental phenomena have also their relations, which are likewise fixed and uniform; though it may be more difficult to ascertain the truth in regard to them, than in the relations of material things.

The relations or sequences of mental phenomena are to be considered in two points of view; namely, relations to each other, and relations to external things. In regard to both, it seems necessary to divide the phenomena themselves into three classes.

1. Simple intellect, or those powers by which we perceive, remember, and combine facts or events, and compare them with each other: such as perception, memory, imagination, and judgment.

2. Passive emotions, or those by which the mind is affected by certain pleasurable or painful feelings, which are, or may be, confined entirely to the individual who is the subject of them.

3. Active emotions, or those which tend directly to influence the conduct of men, either as moral and responsible beings, or as members of society.

In all these classes, mental phenomena have certain relations to each other and to external things, the investigation of which is the object of particular branches of science; and these lead to certain arts or practical rules which are founded upon them.

Intellectual science investigates the laws and relations of the processes of simple intellect, as perception, memory, imagination, and judgment; and the proper cultivation and regulation of these is the object of the practical art of intellectual education.

The passive emotions may be influenced or excited in two ways; namely, through our relations o other sentient and intelligent beings, and by ma

terial or inanimate things. To the former head are referable many of the tenderest and most interesting feelings of our nature, as love, hope, joy, and sorrow. To the latter belong those emotions which come under the subject of taste, or the tendencies of certain combinations of material things to excite emotions of a pleasurable or painful kind,-as our impressions of the sublime, the beautiful, the terrible, or the ludicrous. The practical rules or processes, connected with the science of the passive emotions, arrange themselves into two classes, corresponding to the two divisions now mentioned. To the former belong the regulation of the emotions, and all those rules of conduct not exactly referable to the higher subject of morals, which bear an extensive influence on the ties of friendship-and the relations of social and domestic intercourse. To the latter belong chiefly those processes which come under the head of the fine arts; namely, the arts of the painter, the sculptor, the architect, the musician,— perhaps we may add, the poet and the dramatist.

The active emotions, or those which influence human conduct, are referable to two classes; namely, those which affect men individually as moral and responsible agents, and those which affect them as united in large bodies constituting civil society. The cultivation of the emotions of the former class, and the investigation of the motives and principles by which they are influenced, belong to the high subjects o morals and religion. The investigation and control of emotions of the latter class come under the science of politics; and the practical art, founded upon it, relates to those measures by which the statesman attempts to control and regulate the conduct of masses of mankind united as members of a great civil community.

In medical science, the objects of our researches are chiefly the relations between external things and the living powers of animal bodies, and the re

lations of these powers to each other;-more particularly in regard to the tendencies of external things to produce certain changes upon living bodies, either as causes of disease or as remedies. The practical art founded upon this science leads to the consideration of the means by which we may avail ourselves of this knowledge, by producing, in the one case, actions upon the body which we wish to produce, and in the other, by counteracting or avoiding actions which we wish to prevent.

In all these sciences, and the practical arts which are founded upon them, the general principles are the same; namely, a careful observation of the natural and uniform relations or tendencies of bodies towards each other; and a bringing of those tendencies into operation for the production of results. All art, therefore, must be founded upon science, or a correct knowledge of these relations; and all science must consist of such a careful observation of facts in regard to the relations, as shall enable us confidently to pronounce upon those which are fixed and uniform. He who follows certain arts or practical rules, without a knowledge of the science on which they are founded, is the mere artisan or the empiric; he cannot advance beyond the precise rules which are given him, or provide for new occurrences and unforeseen difficulties. In regard to science, again, when the relations are assumed hastily, or without a sufficiently extensive observation of facts, the process constitutes false science, or false induction; and when practical rules are founded upon such conclusions, they lead to error and disappointment in the result which is expected.

The views which have now been referred to lead us to principles by which the sciences are distinguished into those which are certain and those which are, in a greater or less degree, uncertain. The certainty of a science depends upon the facility and

correctness with which we ascertain the true relations of things, or trace effects to their true causes, and causes to their true effects, and calculate upon the actions which arise out of these relations taking place with perfect uniformity. This certainty we easily attain in the purely physical sciences, or those in which we have to deal only with inanimate matter. For in our investigation of the relations of ma terial bodies, whether mechanical or chymical, we contrive experiments, in which by placing the bodies in a variety of circumstances towards each other, and excluding all extraneous influence, we come to determine their tendencies with perfect certainty. Having done so, we rely with confidence on these tendencies continuing to be uniform; and should we in any instance be disappointed of the result which we wish to produce, we are able, at once, to detect the nature of some incidental cause by which the result has been prevented, and to obviate the effect of its interference. The consequence of this accurate knowledge of their relations is, that we acquire a power over material things; but this power is entirely limited to a certain control and direction of their natural relations; and we cannot change these relations in the smallest particular. Our power is of course also limited to those objects which are within the reach of our immediate influence; but with respect to those which are beyond this influence, as the heavenly bodies, the result of our knowledge appears in a manner not less striking, in the minute accuracy with which we are enabled to foretel their movements, even at very distant periods. I need only mention the correctness with which the astronomer calculates eclipses and the appearance of comets.

With these characters of certainty in the purely physical sciences, two sources of uncertainty are contrasted in those branches of science in which we have to deal with mental operations, or with the