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OBSERVATORY LIBRARY

SIX LECTURES,

DELIVERED IN 1868, BEFORE THE SOCIETY OF
APOTHECARIES OF LONDON.

HENRY E. ROSCOE, B.A, Ph.d. F.E.S.

PROFESSOR OF CHEMISTRY IN OWENS COLLEGE, MANCHESTER.

WITH APPENDICES, COLOURED PLATES, AND ILLUSTRATIONS.

D. APPLETON AND CO. GRAND STREET.

1869.

[The Light of Translation and Reproduction is reserved.]

LONDON:

It. CLAY, SONS, AND TAYLOR, PRINTERS,

BREAD STREET HILL.

PREFACE.

In publishing the following Lectures I have endeavoured to preserve the elementary character which they naturally assumed in delivery, thinking it best to give further detail in a series of Appendices. If the book thus assumes less of the character of a complete treatise than might be desirable, it gains in value for the general reader, inasmuch as the science of Spectrum Analysis is at present in such a rapid state of growth that much of the subject is incomplete, and, therefore, necessarily unsuited to the public at large. I hope, however, that the addition of many extracts from the most important Memoirs on the subject may prove interesting to all, as it will certainly be useful to those specially engaged in scientific inquiry, as indicating the habits of exact research and accurate observation by which alone such striking results have been attained. For the permission to reproduce exact copies of Kirchhoff's, Angstrom's, and Huggins' maps, together with the Tables of the positions of the dark solar and bright metallic lines, I have to thank the above-named gentlemen. These maps will render the work valuable to the student for a reference, whilst the chromolithographic plates of the spectra of the metals of the alkalies and alkaline earths, and of the spectra of the stars, nebulae, and non-metallic elements, serve to give some idea of the peculiar beauty of the real phenomena thus represented.

Since last summer, when these Lectures were delivered, our knowledge of the constitution of the sun especially has made giant strides, and although I have been unable to introduce these newest facts into the text of the Lectures, I have still brought forward the most important of these discoveries in the Appendices to Lecture V.

As the latest news on this subject, I may mention the arrangement contrived by Mr. Huggins, by which the wonderful changes of the red solar prominences can all be viewed at once; changes so enormously rapid that Mr. Lockyer has observed one of these red solar flames, 27,000 miles in length, disappear altogether in less than ten minutes. Mr. Lockyer has also succeeded in seeing in the flames the red (c) line of hydrogen, as well as the line in the violet, which he finds corresponds to the line marked 2796 on KirchhofFs map, and not, as was supposed, identical with Fraunhofer's line G.

At the end of the volume will be found a tolerably complete List of Memoirs forming the literature on the subject.

My thanks are due to Mr. J. D. Cooper and Mr. Collings for the very great care which they have bestowed upon the illustrations, and especially upon the difficult task of reproducing Kirchhoff's maps in four tints.

H. E. R.

Manchester, April 1869.

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