ning. Although scientific schools had been previously established, both at Cambridge and at New Haven, yet Prof. Cooke was probably the first to introduce into our American colleges the experimental method of teaching physical science. He was, at first, greatly hampered by the inflexible recitation system, then universal, and success was only gained after many trials; but Harvard College may now claim to offer its undergraduates as broad and thorough instruction in the various departments of chemistry, including mineralogy, as any similiar institution in the world. Like most American men of science, Prof. Cooke's first duty was to teach, and his time and energy have accordingly been chiefly spent in developing methods of science-teaching, in building laboratories, in making collections, and in providing the various means of scientific instruction.
In connection with his teaching Prof. Cooke has published the following books:
"Chemical Problems and Reactions, to accompany Stöckhardt's Elements of Chemistry," in 1857; "Elements of Chemical Physics," in 1860; "Principles of Chemical Philosophy," in 1869.
In a notice of the last book the London Chemical News says: "So far as our recollection goes, we do not think that there exists in any language a book on so difficult a subject as this, so carefully, clearly, and lucidly written;" and in noticing the same book the American Journal of Science says: "To Prof. Cooke, more than to any American, is due the credit of having made chemistry an exact and disciplinary study in our colleges."
Prof. Cooke has given many courses of popular lectures in different cities—Lowell, Worcester, Brooklyn, Baltimore, and Washington—besides five courses at the Lowell Institute in Boston. His course of lectures at the Brooklyn Institute, in 1860, was subsequently published under the title of "Religion and Chemistry; or, Proofs of God's Plan in the Atmosphere and its Elements" (1864). In these discourses he aimed to show that the argument for design is not invalidated by the theories of evolution.
A course of lectures on electricity at the Lowell Institute, Boston, in the winter of 1868-'69, was followed by the publication, in the Journal of the Franklin Institute, of a series of papers on the "Absolute System of Electrical Measurements" and on the "Theory of the Voltaic Battery." In the last he developed a new theory of electricity, which has also been embodied in the later editions of his "Chemical Philosophy." This theory, like that of Dufay, admits two electrical fluids; but it regards these as separable constituents of the ether of space. These ethereal fluids, more or less blended, form an atmosphere around every molecule held in place by the immense force of molecular attraction; and when, by the various causes of electrical disturbance, the electrical ethers become more or less isolated on the same or on different molecules the two tend to flow
