BALFOUR STEWART, LL.D., F.R.S. PROFESSOR OF NATURAL PHILOSOPHY, OWENS COLLEGE, MANCHESTER. [The Right of Translation and Reproduction is reserved.] PREFACE. IN the following pages I have endeavoured to bring before the student, in an elementary manner, the most important of those laws which regulate the phenomena of nature; but the subject is so extensive that a detailed account cannot be given in such a treatise as this. The various branches of the subject have been so arranged that the student may perceive the connection between them. For many particulars of this arrangement I am indebted to my friend Professor Tait. An account of the various active agents, heat, light, electricity, &c., must always form a large portion of a work on Physics. These have been regarded as varieties energy—the laws of energy forming, as it were, the thread upon which the various divisions of the subject are strung together. The description of these agents is Lot, of course, materially different from that usually given; bat by this means of connecting them together, the adent is constantly reminded of the paramount imporQance of the laws of energy. For the plate representing various spectra, which forms the frontispiece, and for that of the Kew spectroscope, I am indebted to my friend Mr. Lockyer; and I have much pleasure in thanking Mr. George Whipple, of the Kew Observatory, for many suggestions while the work was passing through the press; and also Mr. J. D. Cooper and Mr. Collings for the care they have bestowed upon the illustrations. MANCHESTER, October 1870. |