That mental progress is advanced by scientific discovery is a common circumstance. Our ideas of facts, our knowledge of general principles, our views of man, of nature, and of the Universe; and even our modes of thought, have been gradually and profoundly changed by the new knowledge acquired by means of scientific research. This truth is capable of being most extensively illustrated by a multitude of facts in the whole of the sciences, and in the arts, manufactures, and other subjects dependent upon science. For example, in astronomy, great changes, produced by the results of scientific discovery have taken place in our ideas respecting the magnitude of Space and of the Heavenly bodies, the constitution, form, and motion of the Earth, the functions of the Sun and Moon, the distances of the Sun and fixed Stars, the nature of eclipses and comets; and a great many other matters. In terrestrial physics, the mental advances have been equally great in our ideas respecting the causes of tides and of winds, the pressure of the atmosphere, the existence and course of the Gulf Stream, the physical conditions of the Equator and Poles, the conditions upon which day and night, summer and winter depend, the depth of the ocean, the height of the atmosphere, the cause of rainbows, of {86} rain, hail, snow, mist and dew, of thunder and lightning, the composition of air, water, mineral, and organic substances, and other most numerous and varied phenomena. In the subjects of heat, light, electricity, magnetism, chemistry, vegetable and animal physiology, psychology and morality, and the more concrete subjects depending upon them, such as politics, trade, commerce, government, &c., our ideas have equally advanced, in consequence of scientific research; and to fully describe the mental progress resulting from discovery in nearly all branches of human knowledge would require a series of books to be written on the History of all the Sciences. Other causes also, which I need hardly mention, besides scientific discovery, have of course contributed to the mental progress of mankind. We arrive at true ideas, not only by the more certain and systematic process employed in scientific research, but largely also by the uncertain method of trusting to instinct and habit, by adopting dogmatic opinions, and by the semi-scientific plan of following empirical rules.