rise further. When the tips were hot enough, vaporising carbon became
incandescent giving an intense blue-white light. It was not a cheap method of
lighting however and the intense brightness and UV radiation meant it was
not a practical proposition for domestic use. The term ‘arc lamp’ remains in
use today for bright lights often used to illuminate work spaces, but their
technology is entirely different. But by 1890 there were over 130,000 arc
lamps in use nightly for lighting public spaces such as ‘Broadway’, NY, in the
United States for example, each producing around 700 ‘candlepower’ (cp).
3
For domestic and commercial lighting, the ‘incandescent’ lamp was favoured,
and like the arc lamp it too had a history of many years. The ‘light bulb’—an
evacuated glass bulb containing an electrically heated thread-like ‘filament’—
was made a practical reality by Joseph Wilson Swan and Thomas Alvar
Edison. Almost universally in these early attempts, carbon produced by a
variety of mechanisms, was the preferred choice for the ‘filament’ because it
had the highest melting/sublimation point of any element—the key to a
practical cost effective incandescent light bulb being the longevity of the
filament. The breakthrough for Edison and Swan came in 1879 when they
independently developed an incandescent bulb that lasted a practical length of
time—at best about 13 h! But the contributions of many others were also
important and two of these already had a profound influence on Robert’s life.
Sir William Crookes—who in 1898 had exhorted chemists to rid the world
of its dependency on Chile saltpetre—had earlier developed a carbon filament
from animal and vegetable fibres, ‘parchmentised’ in ‘cuprammonic’ chloride.
His bulbs were tall and narrow with straight sides and his filament was ‘M’
shaped. His main contribution to the light bulb however, was in the vacuum
pumps that he helped develop with Hermann Sprengel
4 for removing air
from the tubes. Without these pumps, the practical light bulb we recognize
today could not have been developed. But for Robert, there was a much more
familiar player in the form of Walther Nernst, whose engagement with the
technology of electric lighting almost by itself defines its importance. Nernst’s
lifelong interest of course was in the interaction of heat and matter and he
found various minerals that became incandescent when heated. These
materials were first used for gas lamps but he quickly saw the possibility of
heating them by electricity. Unlike carbon filaments, the materials he used
were not subject to oxidation at the temperature of incandescence and so
there was no need to enclose them in an evacuated bulb—with obvious
engineering and manufacturing advantages. Any enclosing bulb was used
simply to protect and isolate the hot element (the ‘glower’) from its environment. The glower itself was made from oxides of the rare earth elements.
Nernst lamps gave a higher luminosity at a lower energy consumption than
9 The Auergesellschaft, Berlin
191
incandescent giving an intense blue-white light. It was not a cheap method of
lighting however and the intense brightness and UV radiation meant it was
not a practical proposition for domestic use. The term ‘arc lamp’ remains in
use today for bright lights often used to illuminate work spaces, but their
technology is entirely different. But by 1890 there were over 130,000 arc
lamps in use nightly for lighting public spaces such as ‘Broadway’, NY, in the
United States for example, each producing around 700 ‘candlepower’ (cp).
3
For domestic and commercial lighting, the ‘incandescent’ lamp was favoured,
and like the arc lamp it too had a history of many years. The ‘light bulb’—an
evacuated glass bulb containing an electrically heated thread-like ‘filament’—
was made a practical reality by Joseph Wilson Swan and Thomas Alvar
Edison. Almost universally in these early attempts, carbon produced by a
variety of mechanisms, was the preferred choice for the ‘filament’ because it
had the highest melting/sublimation point of any element—the key to a
practical cost effective incandescent light bulb being the longevity of the
filament. The breakthrough for Edison and Swan came in 1879 when they
independently developed an incandescent bulb that lasted a practical length of
time—at best about 13 h! But the contributions of many others were also
important and two of these already had a profound influence on Robert’s life.
Sir William Crookes—who in 1898 had exhorted chemists to rid the world
of its dependency on Chile saltpetre—had earlier developed a carbon filament
from animal and vegetable fibres, ‘parchmentised’ in ‘cuprammonic’ chloride.
His bulbs were tall and narrow with straight sides and his filament was ‘M’
shaped. His main contribution to the light bulb however, was in the vacuum
pumps that he helped develop with Hermann Sprengel
4 for removing air
from the tubes. Without these pumps, the practical light bulb we recognize
today could not have been developed. But for Robert, there was a much more
familiar player in the form of Walther Nernst, whose engagement with the
technology of electric lighting almost by itself defines its importance. Nernst’s
lifelong interest of course was in the interaction of heat and matter and he
found various minerals that became incandescent when heated. These
materials were first used for gas lamps but he quickly saw the possibility of
heating them by electricity. Unlike carbon filaments, the materials he used
were not subject to oxidation at the temperature of incandescence and so
there was no need to enclose them in an evacuated bulb—with obvious
engineering and manufacturing advantages. Any enclosing bulb was used
simply to protect and isolate the hot element (the ‘glower’) from its environment. The glower itself was made from oxides of the rare earth elements.
Nernst lamps gave a higher luminosity at a lower energy consumption than
9 The Auergesellschaft, Berlin
191