was cut
short by the appearance of metal filaments.

In 1803 a new element was discovered and named tantalum. It is a dark,
lustrous, hard metal. Pure tantalum is harder than steel; it may be
drawn into fine wire; and its melting-point is very high (about
5100 deg.F.). It is seen to possess properties desirable for filaments, but
for some reason it did not attract attention for a long time. A century
elapsed after its discovery before von Bolton produced the first
tantalum filament lamp. Owing to the low electrical resistance of
tantalum, a filament in order to operate satisfactorily on a standard
voltage must be long and thin. This necessitates storing away a
considerable length of wire in the bulb without permitting the loops to
come into contact with each other. After the filaments have been in
operation for a few hundred hours they become brittle and faults
develop. When examined under a microscope, parts of the filament
operated on alternating current appear to be offset. The explanation of
this defect goes deeply into crystalline structure. The tantalum
filament was quickly followed by osmium and by tungsten in this country.

The osmium filament appeared in 1905 and its invention is due to
Welsbach, who had produced the marvelous gas-mantle. Owing to its
extreme brittleness, osmium was finely divided and made into a paste of
organic material. The filaments were squirted through dies and, after
being formed and dried, they were heated to a high temperature. The
organic matter disappeared and the fine metallic particles were
sintered. This made a very brittle lamp, but its high efficiency served
to introduce it.

In 1870 when Scheele discovered a new element, known in this country as
tungsten, no one realized that it was to revolutionize artificial
lighting and to alter the course of some of the byways of civilization.
This metal--which is known as "wolfram" in Germany, and to some extent
in English-speaking countries--is one of the heaviest of elements,
having a specific gravity of 19.1. It is 50 per cent. heavier than
mercury and nearly twice as heavy as lead. It was early used in German
silver to the extent of 1 or 2 per cent. to make platinoid, an alloy
possessing a high resistance which varies only slightly as the
temperature changes. This made an excellent material for electrical
resistors. The melting-point of tungsten is about 5350 deg.F., which makes
it desirable for filaments, but it was very brittle a