d various kinds of bamboo from other
parts of the world. Thin filaments of split bamboo eventually proved the
best material up to that time. He made many lamps containing filaments
of this material, and even until 1910 bamboo was used to some extent in
certain lamps.

Of these early days, Edison said:

It occurred to me that perhaps a filament of carbon could be
made to stand in sealed glass vessels, or bulbs, which we were
using, exhausted to a high vacuum. Separate lamps were made in
this way independent of the air-pump, and, in October, 1879, we
made lamps of paper carbon, and with carbons of common sewing
thread, placed in a receiver or bulb made entirely of glass,
with the leading-in wires sealed in by fusion. The whole thing
was exhausted by the Sprengel pump to nearly one-millionth of
an atmosphere. The filaments of carbon, although naturally
quite fragile owing to their length and small mass, had a
smaller radiating surface and higher resistance than we had
dared hope. We had virtually reached the position and condition
where the carbons were stable. In other words, the incandescent
lamp as we still know it to-day [1904], in essentially all its
particulars unchanged, had been born.

After Edison's later success with bamboo, Swan invented a process of
squirting filaments of nitrocellulose into a coagulating liquid, after
which they are carbonized. Very fine uniform filaments can be made by
this process and although improvements have been made from time to time,
this method has been employed ever since its invention. In these later
years cotton is dissolved in a suitable solvent such as a solution of
zinc chloride and this material is forced through a small diamond die.
This thread when hardened appears similar to cat-gut. It is cut into
proper lengths and bent upon a form. It is then immersed in plumbago and
heated to a high temperature in order to destroy the organic matter. A
carbon filament is the result. From this point to the finished lamp many
operations are performed, but a discussion of these would lead far
afield. The production of a high vacuum is one of the most important
processes and manufacturers of incandescent lamps have mastered the art
perhaps more thoroughly than any other manufacturers. At least, their
experience in this field made it possible for them to produce quickly
and on a large scale such devices as X-ray tub