time to time to look at the operations and
receive reports of progress."

The history of the development of the telephone transmitter, phonograph,
incandescent lamp, dynamo, electrical distributing systems from central
stations, electric railway, ore-milling, cement, motion pictures, and
a host of minor inventions may be found embedded in the laboratory
note-books. A passing glance at a few pages of these written records
will serve to illustrate, though only to a limited extent, the
thoroughness of Edison's method. It is to be observed that these
references can be but of the most meagre kind, and must be regarded as
merely throwing a side-light on the subject itself. For instance, the
complex problem of a practical telephone transmitter gave rise to a
series of most exhaustive experiments. Combinations in almost infinite
variety, including gums, chemical compounds, oils, minerals, and metals
were suggested by Edison; and his assistants were given long lists
of materials to try with reference to predetermined standards of
articulation, degrees of loudness, and perfection of hissing sounds. The
note-books contain hundreds of pages showing that a great many thousands
of experiments were tried and passed upon. Such remarks as "N. G.";
"Pretty good"; "Whistling good, but no articulation"; "Rattly";
"Articulation, whispering, and whistling good"; "Best to-night so far";
and others are noted opposite the various combinations as they were
tried. Thus, one may follow the investigation through a maze of
experiments which led up to the successful invention of the carbon
button transmitter, the vital device to give the telephone its needed
articulation and perfection.

The two hundred and odd note-books, covering the strenuous period during
which Edison was carrying on his electric-light experiments, tell on
their forty thousand pages or more a fascinating story of the evolution
of a new art in its entirety. From the crude beginnings, through all
the varied phases of this evolution, the operations of a master mind
are apparent from the contents of these pages, in which are recorded the
innumerable experiments, calculations, and tests that ultimately brought
light out of darkness.

The early work on a metallic conductor for lamps gave rise to some very
thorough research on melting and alloying metals, the preparation of
metallic oxides, the coating of fine wires by immersing them in a great
variety of chemical solutions. Followi