492 THE POPULAR SCIENCE MONTHLY. 



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 min- 

 eralogy, 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 fol- 

 lowing books: 



" Chemical Problems and Reactions, to accompany Stockhardt'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 Ameri- 

 can, is due the credit of having made chemistry an exact and dis- 

 ciplinary study in our colleges." 



Prof. Cooke has given many courses of popular lectures in different 

 cities Lowell, Worcester, Brooklyn, Baltimore, and Washington be- 

 sides 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 " Abso- 

 lute System of Electrical Measurements " and on the " Theory of the 

 Voltaic Battery." In the last he developed a new theory of elec- 

 tricity, 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 im- 

 mense 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 



