men he is obliged to judge of the internal operations by external phenomena; and in this manner a degree of uncertainty attends his investigations, which does not occur in physical science. From this source also has probably arisen much of that difference of opinion which we meet with in regard to the mental powers: for, each inquirer having drawn his observations chiefly from one mind, namely, his own, it was scarcely to be expected that there should not be some diversity, or that facts derived in this manner should possess the character of being universal.

The means by which this difficulty can be removed must consist in an extensive collection of facts, illustrating the phenomena of mind in various individuals, and under a variety of circumstances; and there are several points of view in which the subject is peculiarly adapted to the medical observer. Mental manifestations are greatly modified by the condition of those bodily organs by which the mind holds intercourse with external things, especially the brain. It becomes therefore a matter of the greatest interest to ascertain the manner in which the manifestations of mind are affected by diseases of these organs, as well as to observe their condition in that remarkable class of affections commonly called diseases of the mind. Besides, in the affections which are referable to both these classes, we often meet with manifestations of the most interesting kind, and such as are calculated to illustrate, in a very striking manner, important points in the philosophy of the mental powers. It is thus in the power of the observing physician to contribute valuable facts to the science of mind; and it is almost unnecessary to add, that the study may be turned to purposes of immediate importance to his own inquiries. He does not need to be reminded how much the mind acts upon the body-that mental emotions often prove sources of disease, or causes by which his remedies are modified or counteracted-and that, on the other hand, a

remedy may often be introduced by the mind, capable of composing tumults of the corporeal functions, which cannot be tranquillized by physical aid.

From the deep interest which the philosophy of mind thus presents to the medical inquirer, I have been induced to attempt a slight outline of this important subject. In doing so, I do not profess to offer any thing new or original. My object is to present to the younger part of the profession some leading facts, which may serve to direct their further inquiries on a subject of great and general interest.

This slight outline of the functions of mind will be followed by an attempt to trace the rules which ought to guide us in applying these powers to the investigation of truth in any department of knowledge. The practical application of the subject will lead to a general view of the laws or principles of philosophical inquiry and inductive science, and will then be directed in a more particular manner to the purposes of medical investigation. This is attempted in the hope that the principles which it is meant to convey may be of use in giving precision to medical investigations, by illustrating those rules of sound induction which are acted upon in other departments of science.

B2

PRELIMINARY OBSERVATIONS

ON THE

GENERAL NATURE AND OBJECTS
OF SCIENCE.

By the will of the Almighty Creator, all things in nature have been placed in certain relations to each other, which are fixed and uniform. In other words, they have been endowed with capacities of acting and capabilities of being acted upon, according to certain uniform laws; so that their actions take place in the same manner in every instance in which the same bodies are brought together under similar circumstances. We have a conviction, which appears to be original and instinctive, of the general uniformity of these relations; and in this consists our confidence in the regularity of all the operations of nature. But the powers or principles on which the relations depend are entirely hidden from us in our present state of being. The province of human knowledge is merely to observe the facts, and to trace what their relations or sequences are. This is to be accomplished only by a careful and extensive observation of the facts as they pass before us, and by carefully distinguishing their true or uniform relations from connexions which are only incidental and temporary.

In our first observation of any particular series of facts or events, we find a certain number of them placed together in a state of contiguity or apparent connexion. But we are not entitled from this to assume the connexion to be any thing more than incidental juxtaposition. When, in the further progress of observation, we find the same events occurring a certain number of times, in the same relations or sequences to each other, we suspect that their connexion is not merely that of incidental contiguity. We begin to believe that there exists among them such a relation as leads us, when we meet with some of these events, to expect that certain others are to follow. Hence is excited our idea of power in reference to these events, or of the relation of cause and effect. This relation, however, according to the utmost extent of our knowledge of it in any individual instance, is founded entirely upon the fact of certain events uniformly following one another. But when we have found, by sufficient observation, the particular events which do thus follow one another, we conclude that there is a connexion, whatever may be the nature of it, in consequence of which the sequence which we have observed will continue to recur in the same fixed and uniform manner. In other words, we conclude with confidence, that when we observe the first of two such events, the second will follow; and that when we observe the second, the first has preceded it. The first we call cause, the second effect. Thus our general confidence in the uniformity of the true relations or sequences of events is an original or instinctive principle, and not the result 'of experience; but it is by experience that we ascertain what the individual sequences are which observe this uniformity; or, in other words, learn to distinguish connexions which consist of incidental contiguity from those which constitute true and uniform relations.

The natural tendency of the mind appears indeed