Entered according to Act of Congress, in the year 1874, by ARTHUR SEarle, In the Office of the Librarian of Congress, at Washington. LIBRARI. 47531 CAMBRIDGE: PRESS OF JOHN WILSON AND SON. 1 PREFACE. No one, probably, would maintain that a student who had no intention of attempting to read, speak, or write the Greek language, could spend his time. profitably in committing a Greek grammar to memory; yet methods analogous to this are still sometimes employed in the study of science. No practical man, however, needs to be told that learning any number of scientific facts from books cannot be called the study of the subject to which those facts relate, but can only be called picking up general information about the subject. It is well to have a stock of general information about many subjects apart from those which we study thoroughly; but general information can never be exact, and its acquisition ought to constitute the recreative, not the laborious, part of education. The study of a Greek grammar written in Latin will improve the student's knowledge of Latin, but will be worthless as a means of teaching him Greek, unless he follows it up by practice in reading that language. In like manner, the knowledge of any natural science, obtained only from a text-book, is scarcely valuable enough to warrant the consumption of much time in committing the book to memory, although its statements may be made with all the precision attainable by the use of mathe |