SIX LECTURES, DELIVERED IN 1868, BEFORE THE SOCIETY OF BY Enfield SHENRY E. ROSCOE, B.A. PH.D. F.R.S. PROFESSOR OF CHEMISTRY IN THE OWENS COLLEGE, MANCHESTER. WITH APPENDices, colourED PLATES, AND ILLUSTRATIONS. THIRD EDITION. London: MACMILLAN AND CO. 1873. [The Right of Translation and Reproduction is reserved.] Harvard College Library, LONDON: R. CLAY, SONS, AND TAYLOR, PRINTERS, BREAD STREET HILL. PREFACE TO THE THIRD EDITION. In this edition of my Lectures on Spectrum Analysis I have endeavoured to introduce all the more important facts and conclusions resulting from investigations which have been carried on during the last two years. As regards the general subject, the interesting question as to whether an elementary body possesses more than one spectrum has received much attention; and from experiments on the spectrum of nitrogen, referred to in Lecture IV., it seems that we must, with Ångström, probably answer this question in the negative. Another important inquiry, though one as yet far from being in a satisfactory position, refers to the question as to whether the wave-lengths of the various bright lines in the spectrum of an element stand in any simple or harmonic ratio to one another: the results of observations on this point are found on page 317. The secret of the singular spectrum of the Bessemer flame has at length been unravelled; it proves to be identical with that of oxide of manganese: a drawing of the two spectra is found on page 175. In solar and stellar chemistry the additions to our knowledge have been numerous and important. The phenomena of two total solar eclipses have been carefully observed by spectroscopists and astronomers of all nations; and, thanks to their efforts, whilst much still remains to be settled concerning the solar corona and the zodiacal- and auroral-lights, it is certain that our knowledge of the chemistry and physics of our luminary has progressed immensely. Indeed, the discussion of the details of the observations, and of the different views of the several observers, has already quite passed beyond the limits of a work of this kind, so that I have felt obliged to confine myself to a brief Summary, at the end of Lecture V., of the chief and generally recognized results of later inquiry. In order, however, to render more evident the basis upon which our knowledge of solar chemistry rests, I have (with the Author's kind permission) introduced at page 308 an extract from Professor Balfour Stewart's admirable chapter on Radiation and Absorption. With respect to the metals whose presence has been detected in the sun, I have to notice an error which |