With the exception, however, of poetry, architecture, and generally of the arts that are addressed to the taste and the imagination, for which nations in an early stage of civilisation seem to have a peculiar aptitude, the arts of an unscientific age contain many rules ineffectual for their intended purposes, and many that are positively opposed to them. Thus the medicine of the middle ages ordered plants with yellow flowers to be used in cases of jaundice, and those with red flowers in fevers, and directed fomentations and ointments to be applied not to the wound but to the sword. At length a man arrives with wider views or less docile habits of mind, who is not satisfied to obey what often appear to him to be arbitrary rules, though he is told that they are the results of experience. He endeavours to account for the effects which he sees produced, that is to say, to refer them to some general laws of matter or of mind. To do this is to create a science. As soon as scientific habits of thought prevail, men are teazed by any appearance for which they cannot account. Their first motive is to question its reality. Evidence of mesmeric clairvoyance has been produced enough to satisfy a sceptical inquirer, if the phenomenon itself could be accounted for. But we cannot refer it to any general law, and therefore the greater part of those who think about it, deny its existence; many suspend their opinion, and scarcely any are complete believers. If its existence should ever be thoroughly established, the whole scientific world will be engaged in searching for the general principles to which it is to be referred; for no one will be satisfied with accepting it as an insulated unexplained fact. I have said that a single art generally draws its premises from many different sciences. So a single science generally affords premises to many different arts. How numerous are the sciences which are applicable to the art of war. How numerous are the arts which depend in part on the principles of chemistry. And it is obvious that every increase of human knowledge must increase the influence of science on art. Under this influence many new rules are laid down, and many, which were supposed to be founded on experience, are abandoned as unnecessary or injurious. The art becomes in some respects more simple and in others more complex: more complex because its precepts become more diversified and more detailed; more simple because, instead of being thrown together with little apparent connection, they are grouped under the general principles supplied by science.