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THE TELEPHONE




By Professor A. E. Dolbear


_THE TELEPHONE_

With directions for making a Speaking Telephone Illustrated 50 cents


_THE ART OF PROJECTING_

A Manual of Experimentation in Physics, Chemistry, and Natural History,
with the Porte Lumiere and Magic Lantern New Edition Revised Illustrated
$2.00


_MATTER, ETHER, AND MOTION_

The Factors and Relations of Physical Science Illustrated $1.75


          Lee and Shepard Publishers Boston




THE TELEPHONE:

AN ACCOUNT OF THE

_Phenomena of Electricity, Magnetism, and Sound,_

AS INVOLVED IN ITS ACTION.

WITH DIRECTIONS FOR MAKING

A SPEAKING TELEPHONE.

BY

PROF. A. E. DOLBEAR,

TUFTS COLLEGE,

AUTHOR OF "THE ART OF PROJECTING," ETC.

          BOSTON:
          LEE & SHEPARD, PUBLISHERS.




          COPYRIGHT,
          1877,
          BY A. E. DOLBEAR.




PREFACE.


THE popular exhibitions of the speaking-telephone during the past six
months, together with numerous newspaper articles, have created a
widespread interest in the instrument; and it has been thought that a
small book explanatory of its action would meet a public want.

It has seemed to be necessary to call attention to the various phenomena
and inter-actions of the forces involved; and hence the author has
attempted to make plain and intelligible the phenomena of electricity,
magnetism, and sound. Cuts have been inserted where they could be useful
in making the mechanical conditions more intelligible; and a table of
tone-composition has been devised, which shows at a glance the
constituents of the sounds of various musical instruments.

As the speaking-telephone, in which magneto-electric currents were
utilized for the transmission of speech and other kinds of sounds, was
invented by me, I have described at some length my first instrument, and
have also given explicit directions for making a speaking-telephone
which I know, by trial, to be as efficient as any hitherto made; but
nothing in the book is to be taken as a dedication of the invention to
the public, as steps have already been taken to secure letters-patent
according to the laws of the United States.

                                                       A. E. DOLBEAR.

COLLEGE HILL, MASS.




THE TELEPHONE.


ELECTRICITY.

SOME of the phenomena of electricity are manifested upon so large a
scale as to be thrust upon the attention of everybody. Thus lightning,
which accompanies so many showers in warm weather in almost every
latitude, has always excited in some individuals a superstitious awe, as
being an exhibition of supernatural agency; and probably every one feels
more or less dread of it during a thunder-shower, and this for the
reason that it affects so many of the senses at the same time. The flash
may be blinding to the eyes if near to us; the thunder may be deafening
to the ears, and so powerful as to shake the foundations of the hills,
and make the ground upon which we stand to sensibly move: these with the
remembered destructive effects that have been witnessed, of buildings
demolished and large trees torn to splinters in an instant, are quite
sufficient to raise a feeling of dread in the strongest mind. In the
polar regions, both north and south, where thunder-storms are less
frequent, the atmospheric electricity assumes the form called the aurora
borealis, or the aurora australis, according as it is seen north or
south of the equator.

More than two thousand years ago it was noticed by the Greeks that a
certain kind of a mineral which was thrown up on the shores of the
Mediterranean Sea, when rubbed would attract light bodies, such as
shreds of silk or linen and bits of paper. To this substance they gave
the name of Elektron, and the property developed thus by friction was
afterwards called electricity. In 1600 Dr. Gilbert, physician to Queen
Elizabeth, published a book in which he described numerous experiments
demonstrating that electricity could be developed by friction upon a
great variety of substances, such as stones, gems, and resins. The first
machine for developing electricity was made by Otto von Guericke of
Magdeburg, about 1680. His machine