The original phonograph, as invented by Edison, remained in its crude and immature state for almost ten years--still the object of philosophical interest, and as a convenient text-book illustration of the effect of sound vibration. It continued to be a theme of curious interest to the imaginative, and the subject of much fiction, while its neglected commercial possibilities were still more or less vaguely referred to. During this period of arrested development, Edison was continuously working on the invention and commercial exploitation of the incandescent lamp. In 1887 his time was comparatively free, and the phonograph was then taken up with renewed energy, and the effort made to overcome its mechanical defects and to furnish a commercial instrument, so that its early promise might be realized. The important changes made from that time up to 1890 converted the phonograph from a scientific toy into a successful industrial apparatus. The idea of forming the record on tinfoil had been early abandoned, and in its stead was substituted a cylinder of wax-like material, in which the record was cut by a minute chisel-like gouging tool. Such a record or phonogram, as it was then called, could be removed from the machine or replaced at any time, many reproductions could be obtained without wearing out the record, and whenever desired the record could be shaved off by a turning-tool so as to present a fresh surface on which a new record could be formed, something like an ancient palimpsest. A wax cylinder having walls less than one-quarter of an inch in thickness could be used for 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!