The favor with which this book has been received has brought about the
preparation of this new edition. The present volume has been enlarged
by the addition of certain new material and it has been entirely
reset. Some new illustrations have been made, and in its new dress
the book, it is hoped, will be found to afford an even larger measure
of usefulness. The principles of the science remain the same, but the
author is glad of the opportunity to note certain developments in their
application.
W. H. M.
EDISON LABORATORY, _April, 1915_.