72. It is required, however, for the validity of this method, first that there should be a strict uniformity in the general laws of nature, from which we can infer that what has been will, in the same conditions, be again; and secondly, that we shall be able to perceive and estimate all the conditions with an entire and exclusive knowledge. The first is granted in all physical phænomena; but in those which we cannot submit to experiment, or investigate by some such method as Bacon has pointed out, we often find our philosophy at fault for want of the second. Such is at present the case with respect to many parts of chemistry; for example, that of organic substances, which we can analyse, but as yet can in very few instances recompose. We do not know, and, if we did know, could not perhaps command, the entire conditions of organic bodies (even structurally, not as living), the _form_, as Bacon calls it, of blood, or milk, or oak galls. But in attempting to subject the actions of men to this inductive philosophy, we are arrested by the want of both the necessary requisitions. Matter can only be diverted from its obedience to unvarying laws by the control of mind; but we have to inquire whether mind is equally the passive instrument of any law. We have to open the great problem of human liberty, and must deny even a disturbing force to the will before we can assume that all actions of mankind must, under given conditions, preserve the same necessary train of sequences as a molecule of matter. But if this be answered affirmatively, we are still almost as far removed from a conclusive result as before. We cannot without contradicting every day experience, maintain that all men are determined alike by the same exterior circumstances; we must have recourse to the differences of temperament, of physical constitution, of casual or habitual association. The former alone, however, are, at the best, subject to our observation, either at the time, or, as is most common, through testimony; of the latter, no being, which does not watch the movements of the soul itself, can reach more than a probable conjecture. Sylla resigned the dictatorship, therefore all men, in the circumstances of Sylla, will do the same, is an argument false in one sense of the word circumstances, and useless at least in any other. It is doubted by many, whether meteorology will ever be well understood, on account of the complexity of the forces concerned, and their remoteness from the apprehension of the senses. Do not the same difficulties apply to human affairs? And while we reflect on these difficulties, to which we must add those which spring from the scantiness of our means of observation, the defectiveness and falsehood of testimony, especially what is called historical, and a thousand other errors to which the various “idola of the world and the cave” expose us, we shall rather be astonished that so many probable rules of civil prudence have been