PRACTICAL ELECTRICITY.

A

LABORATORY AND LECTURE COURSE

For First Year Students of Electrical Engineering,

BASED ON THE

International Definitions of the Electrical Units

COMPLETELY RE-WRITTEN

BY

W. E. AYRTON, F.R.S., Assoc. M. INST. C. E.

Dean, and Professor of Electrical Engineering, of the City and Guilds of
London Central Technical College; Technological Examiner in Electric
Lighting and Power Transmission to the City and Guilds Institute;
Past President of the Institution of Electrical Engineers,
and of the Physical Society

VOLUME I.

CURRENT, PRESSURE, RESISTANCE, ENERGY, POWER AND CELLS

First Edition February 1887.
Reprinted September 1887, 1888, 1889, January 1891,

July 1891, 1892, February 1893, April 1893, May 1894, January 1896.
New Revised and Enlarged Edition October 1896,

Reprinted 1897.

75987

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PREFACE.

EXACTLY ten years have elapsed since the preface to the first edition of this book was written-a decade which has seen a vast development in the applications of electricity to industrial purposes, and the springing up in all parts of the kingdom of Technical Schools and Colleges where much attention is devoted to the study of electrotechnics. Hence, to-day it is far more easy for a student to connect his experimental apparatus with the electric light mains and use a comparatively large current at a pressure of 100 volts, than it was in 1886 to obtain a small current at a much lower pressure from the battery which he had to set up for the purpose. This possibility of carrying out the experiments on a larger scale has led to considerable simplification in certain cases; for example, in experimentally determining the heat equivalent of electric energy, it is no longer necessary to distract the beginner's attention with a variety of corrections for the loss of heat, &c.

After many issues of the book had appeared in its original form, it seemed desirable to bring it up to date; and since the practice, not unfrequently resorted to by writers, of inserting a number of new patches in an antiquated ground work, would be out of place in a book which had been written to aid electrotechnical teaching and not for purposes of profit, a proposition was made to entirely rewrite it. This the publishers accepted; and, guided by the success which the book had achieved, they generously, and I anticipate wisely, modified the arrangements so as to justify my devoting a large amount