The following selections will give an idea of the natural science of the Middle Ages. In introducing them, the Editor will attempt to give some connected account of them to show that though their study seems to involve a few difficulties, their explanation is simple, and will not make too great a demand on the reader's patience. From the earliest times men have asked themselves two questions about nature: "Why?" and "How?" Mediaeval science concerned itself with the former; modern science thinks it has learnt that no answer to that question can be given it, and concerns itself with the latter. It thus happens that the more one becomes in sympathy with the thought of our time, the less one can interest one's self in the work of the past, distinguished as it is by its disregard of all we think important, and by its striving for an unattainable goal. It is, however, necessary, if we would enjoy Chaucer, Dante, and Shakespeare, to obtain some notion of that system of the universe from which they drew so many of their analogies. The symbolism of Dante appears to us unnaturally strained until we know that the science of his day saw everything as symbolic. And how could we appreciate the strength of Chaucer's metaphor: "O firste moving cruel firmament, With thy diurnal swegh that croudest ay, And hurtlest all from Est til Occident, That naturally wold hold another way," without some knowledge of the astronomy of his day? Our first extracts explain themselves. They deal with the mystery of the constitution of substances, as fascinating to us as to the early Greeks, and begin with definitions of matter and form. The principal design of early philosophers in physics was to explain how everything was generated, and to trace the different states through which things pass until they become perfect. They observed that as a thing is not generated out of any other indifferently--for example, that marble is not capable of making flesh, all bodies cannot be compounded of principles alone, connected in a simple way, but imagined they could be made up of a few simple compounds. These ultimate compounds, if we may so express it, were their elements. The number of elements was variously estimated, but was generally taken as four--a number arrived at rather from the consideration of the sensations bodies awaken in us, than from the study of bodies themselves. Aristotle gives us the train of thought by which the number is reached. He considers the qualities observed by the senses, classifying them as Heat, Cold, Dryness or Hardness, and Moistness or Capability of becoming liquid. These may partially co-exist, two at a time, in the same substance. There are thus four possible combinations, Cold and dry, Cold and moist, Hot and dry, Hot and moist. He then names these from their prototypes Earth, Water, Fire, and Air, distinguishing these elements from the actual Earth, etc., of everyday life.