Notwithstanding the great number of books which are written, expressly for the use of schools, and which embrace every subject on which instruction is given, it is a lamentable fact, that the catalogue of those which are well adapted to the intended purpose, is a very short one. Almost all of them have been written, either by those who are without experience as teachers, or by teachers, deficient in a competent knowledge of the subjects, on which they treat. Every intelligent person, who has devoted himself to the instruction of youth, must have felt and deplored, the truth of these observations. In most instances, the improvement of a work already in use, will be more acceptable, than one of equal merit would be, which is entirely new; the introduction of a book into schools, being always attended with some difficulty. The "Conversations on Chemistry," written by Mrs. Marcet, had obtained a well-merited celebrity, and was very extensively adopted as a school-book, before the publication of her "Conversations on Natural Philosophy." This, also, has been much used for the same purpose; but, the observation has been very general, among intelligent teachers, that, in its execution, it is very inferior to the former work. The editor of the edition now presented to the public, had undertaken to add to the work, questions, for the examination of learners; and notes, where he deemed them necessary. He soon found, however, that the latter undertaking would be a very unpleasant one, as he must have pointed out at the bottom of many of the pages, the defects and mistakes in the text; whilst numerous modes of illustration, or forms of expression, which his experience as a teacher, had convinced him would not be clear to the learner, must, of necessity, have remained unaltered. He therefore determined to revise the whole work, and with the most perfect freedom, to make such alterations in the body of it, as should, in his opinion, best adapt it to the purpose for which it was designed. Were the book, as it now stands, carefully compared with the original, it would be found, that, in conformity with this determination, scarcely a page of the latter, remains unchanged. Verbal alterations have been made, errors, in points of fact, have been corrected; and new modes of illustration have been introduced, whenever it was thought that those already employed, could be improved; or when it was known, that, from local causes, they are not familiar, in this country. The editor feels assured, that, in performing this task, he has rendered the book more valuable to the teacher, and more useful to the pupil; and he doubts not that the intelligent author of it, would prefer the mode which has been adopted, to that which was at first proposed.