refraction index.

A. PRIVAT-DESCHANEL,

FORMERLY PROFESSOR OF PHYSICS IN THE LYCÉE LOUIS-LE-GRAND,

INSPECTOR OF THE ACADEMY OF PARIS.

TRANSLATED AND EDITED, WITH

EXTENSIVE MODIFICATIONS

By J. D. EVERETT, M. A., D. C. L.. F. R. S., F. R. S. E.,

PROFESSOR OF NATURAL PHILOSOPHY IN THE QUEEN'S COLLEGE, BELFAST.

PREFACE TO THE TENTH EDITION OF

PART III.

THIS Part, even in its original form, was to a great extent rewritten rather

than translated from the French. In the sixth edition it received important

modifications, especially in the department of Current Electricity, in which

there was a complete rearrangement of subjects. A collection of Examples,

with answers, was at the same time added. In the seventh and eighth editions

new matter was introduced under the heads of Storage Batteries, Selenium

Cell and Photophone, Dynamo Machines, Incandescent Electric Lamps, Voss

Machine, and Quadruplex Telegraphy. The ninth edition gave a fuller ac-

count of the Voss Machine, with illustration, an investigation relative to the

work done in moving charged conductors, with application to Thomson's

Quadrant Electrometer, and a table of Electro-chemical Equivalents. The

tenth edition contains a much fuller account of the theory of Thermo-

electricity, some additions relating to electrical Transmission of Power, and

later information respecting Specific Inductive Capacity, and modern Electrical

Machines.

BELFAST, November, 1888.

NOTE PREFIXED TO FIRST EDITION.

THE accurate method of treating electrical subjects which has been established
in this country by Sir Wm. Thomson and his coadjutors, has not yet been
adopted in France; and some of Faraday's electro-magnetic work appears to
be still very imperfectly appreciated by French writers. The Editor has
accordingly found it necessary to recast a considerable portion of the present
volume, besides introducing two new chapters and an Appendix. Potential
and lines of force are not so much as mentioned in the original.