III. What is science, and for what purpose do we study it? I use, of course, the word science in its restricted sense, meaning natural science. For two purposes. Nature is a vast and wonderful machine; its mechanism may well arouse both our astonishment and our admiration. If you have a watch that keeps time so that it does not vary more than two or three minutes in a year you are proud of it, and if you should by chance have a watch that did not vary more than one minute in a year you would be a remarkably humble man if you did not boast of it to your acquaintances. But in the heavens the sun and the planets round it have been keeping time for the centuries, and as yet astronomy has not detected an appreciable variation in its time. What a wonderful mechanism is this! If an inventor should construct a furnace which would keep us warm in winter and cool in summer, no manufacturer would be able to supply the orders. But you have within you a furnace such that although you may go from the land of the Esquimaux with the thermometer 40° below zero, to the tropics with the thermometer 110° above zero, this furnace does not allow the habitation in which you dwell to vary more than four or five degrees. What a wonderful mechanism is this nature which we study! And we study this mechanism partly that we may use it, that we may lay hold on these great forces of nature and make them subservient to our will by understanding the laws which regulate and govern them. But nature is more than a machine; nature is also a book, and a wonderful book, written all over in hieroglyphics that require study for their apprehension. It is more than a mechanism. It is a revelation; and it reveals wondrous things to him who knows how to read it aright. Edison and Morse, Copernicus and Newton—they have interpreted nature on the one side; but Wordsworth, and Longfellow, and Bryant—they have interpreted nature on the other, and the one class of interpretations is as valuable as the other. We study nature as a mechanism that we may know how to use it; we study nature as a book that we may know how to read it.