Knowledge, like wealth hoarded up, has its compound interest, increasing in an almost geometrical ratio. A single discovery in one science sheds a light on all kindred knowledge, which is reflected back again. It is thus that modern discovery proceeds with such rapid steps. A first investigator, groping his way in the dark, cannot form a just idea of the nature and position of objects he may encounter, until time and circumstances make them more familiar. Change of opinion is often produced by more extensive information, and the possession of one new fact at variance with received theories, often leads to an entire reformation of scientific faith. But though our theories alter, our facts remain unchanged; and hence we ought not to be discouraged, remembering that theory is only useful so far as it enables us to collate and reason upon fact. How many are the triumphs which the world of science can boast of, even in our recollection! How much increased is the amount of all knowledge within the present century! We have a new chemistry, a new science of light, that has almost furnished us with one sense more than nature intended we should have. Astronomy has had its Laplace. Mechanics has produced its steam boats and rail roads. Many of the most interesting geographical problems have received their solution—the Niger has been navigated—and the British standard planted on the magnetic pole. The magnet, that riddle of antiquity, has been made to tell its secret in characters of fire. Electricity has furnished its galvanic battery. Physiology has developed more of the nervous structure of man than all the dreams of metaphysicians could have painted. Geology has sprung from the dust and given us animals and plants, the earliest tenants of this earth. New planets have been found, and the periods and orbits of new comets determined. The laws of the elementary constitution of bodies have been fixed, and the relative weight of their _ultimate_ atoms assigned. Botany, mineralogy, and indeed every science, has advanced with rapid steps, and the last half century has added more to human acquirements than the preceding thousand years.