distinctive in the form of a crystal, he cannot distinguish a cube from a square prism, even if he had a goniometer and could use it. And the like impossibility hangs over all the other subjects. To report facts for scientific purposes without some aid from theory, is not only useless, but impossible. When Mr. Spedding says, "I could wish that men of science would apply themselves earnestly to the solution of this practical problem: What measures are to be taken in order that the greatest variety of judicious observations of nature all over the world may be carried on in concert upon a common plan and brought to a common centre:"--he is urging upon men of science to do what they have always done, so far as they have had any power, and in proportion as the state of science rendered such a procedure possible and profitable to science. In Astronomy, it has been done from the times of the Greeks and even of the Chaldeans, having been begun _as soon as_ the heavens were reduced to law at all. In meteorology, it has been done extensively, though to little purpose, because the weather has _not yet_ been reduced to rule. Men of science have shown how barometers, thermometers, hygrometers, and the like, may be constructed; and these may be now read by any one as easily as a clock; but of ten thousand meteorological registers thus kept by ordinary observers, what good has come to science? Again: The laws of the tides have been in a great measure determined by observations in all parts of the globe, _because_ theory pointed out what was to be observed. In like manner the facts of terrestrial magnetism were ascertained with tolerable completeness by extended observations, _then_, and then only, when a most recondite and profound branch of mathematics had pointed out what was to be observed, and most ingenious instruments had been devised by men of science for observing. And even with these, it requires an education to use the instruments. But in many cases no education in the use of instruments devised by others can supersede the necessity of a theoretical and suggestive spirit in the inquirer himself. He must devise his own instruments and his own methods, if he is to make any discovery. What chemist, or inquirer about polarities, or about optical laws yet undiscovered, can make any progress by using another man's experiments and observations? He must invent at every step of his observation; and the observer and theorist can no more be dissevered, than the body and soul of the inquirer.