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 of 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 material 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

powers of living bodies. The first of these depends upon the circumstance, that, in investigating the relations and tendencies in these cases, we are generally obliged to trust to observation alone, as the phenomena happen to be presented to us, and cannot confirm or correct these observations by direct experiment. And as the actual connexions in which the phenomena occur to us are often very different from their true relations, it is in many cases extremely difficult to ascertain the true relations; that is, to refer effects to their true causes, and to trace causes to their true effects. Hence just conclusions are arrived at slowly, and after a long course of occasional observations; and we may be obliged to go on for a long time without acquiring any conclusions which we feel to be worthy of confidence. In these sciences, therefore, there is great temptation to grasp at premature inductions; and when such have been brought forward with confidence, there is often difficulty in exposing their fallacy; for in such a case it may happen, that as long a course of observation is required for exposing the false conclusion, as for ascertaining the true. In physical science, on the other hand, a single experiment may often overturn the most plausible hypothesis, or may establish one which was proposed in conjecture.

The second source of uncertainty in this class of sciences consists in the fact, that, even after we have ascertained the true relations of things, we may be disappointed of the results which we wish to produce, when we bring their tendencies into operation. This arises from the interposition of other causes, by which the true tendencies are modified or counteracted, and the operation of which we are not able either to calculate upon or to control. The new causes, which operate in this manner, are chiefly certain powers in living animal bodies, and the wills, feelings, and propensities of masses of human beings, which we have not the means of reducing to

any fixed or uniform laws. As examples of the uncertain sciences, therefore, we may mention medicine and political economy; and their uncertainty is referable to the same sources, namely, the difficulty of ascertaining the true relations of things, or of tracing effects to their true causes, and causes to their true effects;-and the intervention of new causes which elude our observation, while they interfere with the natural tendencies of things, and defeat our attempts to produce certain results by bringing these into action. The scientific physician well knows the difficulty of ascertaining the true relations of those things which are the proper objects of his attention, and the uncertainty which attends all his efforts to produce particular results. A person, for example, affected with a disease, recovers under the use of a particular remedy. A second is affected with the same disease, and uses this remedy without any benefit; while a third recovers under a very different remedy, or without any treatment at all. And even in those cases in which he has distinctly ascertained true relations, new causes intervene and disappoint his endeavours to produce results by means of these relations. He knows, for example, a disease which would certainly be relieved by the full operation of diuretics;-and he knows various substances which have unquestionably diuretic virtues. But in a particular instance he may fail entirely in relieving the disease by the most assiduous use of these remedies;-for the real and true tendencies of these bodies are interrupted by certain other causes in the constitution itself, which entirely elude his observation, and are in no degree under his control.

It is unnecessary to point out the similarity of these facts to the uncertainty experienced by the statesman in his attempts to influence the interests, the propensities, and the actions of masses of mankind; or to show how often measures which have