ituted such a costly and exhaustive search
throughout the world for the most perfect of natural fibres, he did not
necessarily feel committed for all time to the exclusive use of that
material for his lamp filaments. While these explorations were in
progress, as indeed long before, he had given much thought to the
production of some artificial compound that would embrace not only the
required homogeneity, but also many other qualifications necessary for
the manufacture of an improved type of lamp which had become desirable
by reason of the rapid adoption of his lighting system.

At the very time Mr. McGowan was making his explorations deep in South
America, and Mr. Ricalton his swift trip around the world, Edison,
after much investigation and experiment, had produced a compound which
promised better results than bamboo fibres. After some changes dictated
by experience, this artificial filament was adopted in the manufacture
of lamps. No radical change was immediately made, however, but the
product of the lamp factory was gradually changed over, during the
course of a few years, from the use of bamboo to the "squirted"
filament, as the new material was called. An artificial compound of one
kind or another has indeed been universally adopted for the purpose
by all manufacturers; hence the incandescing conductors in all
carbon-filament lamps of the present day are made in that way. The fact
remains, however, that for nearly nine years all Edison lamps (many
millions in the aggregate) were made with bamboo filaments, and many of
them for several years after that, until bamboo was finally abandoned in
the early nineties, except for use in a few special types which were so
made until about the end of 1908. The last few years have witnessed
a remarkable advance in the manufacture of incandescent lamps in the
substitution of metallic filaments for those of carbon. It will be
remembered that many of the earlier experiments were based on the use of
strips of platinum; while other rare metals were the subject of casual
trial. No real success was attained in that direction, and for many
years the carbon-filament lamp reigned supreme. During the last four
or five years lamps with filaments made from tantalum and tungsten have
been produced and placed on the market with great success, and are now
largely used. Their price is still very high, however, as compared with
that of the carbon lamp, which has been vastly improved in methods o