This substitution of mystical fancies for experimental reasoning gave, in the sixteenth and seventeenth centuries, a doubtful and twilight appearance to the various branches of physical philosophy. The learned and sensible Dr. Webster, for instance, writing in detection of supposed witchcraft, assumes, as a string of undeniable facts, opinions which our more experienced age would reject as frivolous fancies; "for example, the effects of healing by the weapon-salve, the sympathetic powder, the curing of various diseases by apprehensions, amulets, or by transplantation." All of which undoubted wonders he accuses the age of desiring to throw on the devil's back--an unnecessary load certainly, since such things do not exist, and it is therefore in vain to seek to account for them. It followed that, while the opposers of the ordinary theory might have struck the deepest blows at the witch hypothesis by an appeal to common sense, they were themselves hampered by articles of philosophical belief which they must have been sensible contained nearly as deep draughts upon human credulity as were made by the Demonologists, against whose doctrine they protested. This error had a doubly bad effect, both as degrading the immediate department in which it occurred, and as affording a protection for falsehood in other branches of science. The champions who, in their own province, were obliged by the imperfect knowledge of the times to admit much that was mystical and inexplicable--those who opined, with Bacon, that warts could be cured by sympathy--who thought, with Napier, that hidden treasures could be discovered by the mathematics--who salved the weapon instead of the wound, and detected murders as well as springs of water by the divining-rod, could not consistently use, to confute the believers in witches, an argument turning on the impossible or the incredible. Such were the obstacles arising from the vanity of philosophers and the imperfection of their science, which suspended the strength of their appeal to reason and common sense against the condemning of wretches to a cruel death on account of crimes which the nature of things rendered in modern times totally impossible. We cannot doubt that they suffered considerably in the contest, which was carried on with much anger and malevolence; but the good seed which they had sown remained uncorrupted in the soil, to bear fruit so soon as the circumstances should be altered which at first impeded its growth. In the next letter I shall take a view of the causes which helped to remove these impediments, in addition, it must always be remembered, to the general increase of knowledge and improvement of experimental philosophy. LETTER VII.