Humanly speaking, we naturally ascribe discoveries to those who have practically demonstrated them; but when we examine all the clues which have been furnished by previous observers, we frequently have misgivings as to the justice of our decisions. In our admiration of the successful labour of the recent inquirer, we sometimes forget the patient industry of the early pioneer. With regard to those laws which govern the human body, we cannot suppose that the development of them can be destined to progress on any plan less determined than other branches of human inquiry. But in all laws of nature we know that there are interferences which, until explained, serve to obscure or altogether to conceal the law from our view. In relation to the Physiological laws, these interferences are very numerous. 1st. Many are furnished by the physical laws; many more arise from the connection of the physiological with the moral laws, and especially from the abuse of (a responsible) volition. These interferences, however, when their nature is clearly developed, beautifully illustrate the laws they at first obscured; for the common characters of subjects, in which the law is usually exemplified, are brought out into higher relief by the very diversities in the midst of which they occur. The progress of mankind towards a popular familiarity with this fact, is necessarily slow; but still we think it plainly perceptible. An individual life, indeed, however distinguished, represents a mere point in time; it affords little scope for considering, much less for estimating, as they occur, the true meaning of various events, which nevertheless ultimately prove to have had important influence on the progress of knowledge. These are world-wide things, which we must survey as the geologist does the facts concerning which he inquires. We must endeavour to combine, in one view, facts over which long periods of time may have rolled away, with such as are still passing around us. This will frequently suggest designs and relations altogether unobservable by the mere abstract inquirer. In the course of the following pages, a further opportunity may occur for a few remarks on such views; the elaborate discussion of the subject would be altogether beyond our present objects.