receiving a
large number of records, since the maximum depth of the record groove is
hardly ever greater than one one-thousandth of an inch. Later on, and
as the crowning achievement in the phonograph field, from a commercial
point of view, came the duplication of records to the extent of many
thousands from a single "master." This work was actively developed
between the years 1890 and 1898, and its difficulties may be appreciated
when the problem is stated; the copying from a single master of many
millions of excessively minute sound-waves having a maximum width of one
hundredth of an inch, and a maximum depth of one thousandth of an
inch, or less than the thickness of a sheet of tissue-paper. Among the
interesting developments of this process was the coating of the original
or master record with a homogeneous film of gold so thin that three
hundred thousand of these piled one on top of the other would present a
thickness of only one inch!

Another important change was in the nature of a reversal of the original
arrangement, the cylinder or mandrel carrying the record being mounted
in fixed bearings, and the recording or reproducing device being fed
lengthwise, like the cutting-tool of a lathe, as the blank or record was
rotated. It was early recognized that a single needle for forming the
record and the reproduction therefrom was an undesirable arrangement,
since the formation of the record required a very sharp cutting-tool,
while satisfactory and repeated reproduction suggested the use of a
stylus which would result in the minimum wear. After many experiments
and the production of a number of types of machines, the present
recorders and reproducers were evolved, the former consisting of a
very small cylindrical gouging tool having a diameter of about forty
thousandths of an inch, and the latter a ball or button-shaped stylus
with a diameter of about thirty-five thousandths of an inch. By using
an incisor of this sort, the record is formed of a series of connected
gouges with rounded sides, varying in depth and width, and with which
the reproducer automatically engages and maintains its engagement.
Another difficulty encountered in the commercial development of the
phonograph was the adjustment of the recording stylus so as to enter the
wax-like surface to a very slight depth, and of the reproducer so as
to engage exactly the record when formed. The earlier types of machines
were provided with separate screws for eff