bviously necessary to first secure a mold
carrying the record in negative or reversed form. From this could be
molded, or cast, positive copies which would be identical with the
original. While the art of electroplating would naturally suggest
itself as the means of making such a mold, an apparently insurmountable
obstacle appeared on the very threshold. Wax, being a non-conductor,
cannot be electroplated unless a conducting surface be first applied.
The coatings ordinarily used in electro-deposition were entirely out of
the question on account of coarseness, the deepest waves of the record
being less than one-thousandth of an inch in depth, and many of them
probably ten to one hundred times as shallow. Edison finally decided
to apply a preliminary metallic coating of infinitesimal thinness, and
accomplished this object by a remarkable process known as the vacuous
deposit. With this he applied to the original record a film of gold
probably no thicker than one three-hundred-thousandth of an inch, or
several hundred times less than the depth of an average wave. Three
hundred such layers placed one on top of the other would make a sheet no
thicker than tissue-paper.

The process consists in placing in a vacuum two leaves, or electrodes,
of gold, and between them the original record. A constant discharge of
electricity of high tension between the electrodes is effected by means
of an induction-coil. The metal is vaporized by this discharge, and is
carried by it directly toward and deposited upon the original record,
thus forming the minute film of gold above mentioned. The record is
constantly rotated until its entire surface is coated. A sectional
diagram of the apparatus (Fig. 6.) will aid to a clearer understanding
of this ingenious process.

After the gold film is formed in the manner described above, a heavy
backing of baser metal is electroplated upon it, thus forming a
substantial mold, from which the original record is extracted by
breakage or shrinkage.

Duplicate records in any quantity may now be made from this mold by
surrounding it with a cold-water jacket and dipping it in a molten
wax-like material. This congeals on the record surface just as melted
butter would collect on a cold knife, and when the mold is removed the
surplus wax falls out, leaving a heavy deposit of the material which
forms the duplicate record. Numerous ingenious inventions have been made
by Edison providing for a variety of rapid and e