The “T-H” (Thompson-Houston) lamp employed the shunt feed principle.
The carbons were normally separated, being in most types drawn apart
by a spring. A high resistance magnet, shunted around the arc, served
to draw the carbons together. This occurred on starting the lamp and
thereafter the voltage of the arc was held constant by the balance
between the spring and the shunt magnet. As the carbon burned away the
mechanism advanced to a point where a clutch was tripped, the carbons
brought together, and the cycle repeated. Both the T-H and Brush
systems were extensively used in street lighting, for which they were
the standard when the open arc was superseded by the enclosed.
OTHER AMERICAN ARC LIGHT SYSTEMS
[Illustration: THOMSON-HOUSTON ARC LAMP, 1878.
This is an early model with a single pair of carbons.]
[Illustration: THOMSON DOUBLE CARBON ARC LAMP.
This later model, having two pairs of carbons, was commercially used
for many years. This lamp is in the collection of the Smithsonian
Institution.]
Beginning with about 1880, several arc light systems were developed.
Among these were the Vanderpoele, Hochausen, Waterhouse, Maxim,
Schuyler and Wood. The direct current carbon arc is inherently more
efficient than the alternating current lamp, owing to the fact that the
continuous flow of current in one direction maintains on the positive
carbon a larger crater at the vaporizing point of carbon. This source
furnishes the largest proportion of light, the smaller crater in the
negative carbon much less. With the alternating current arc, the large
crater is formed first on the upper and then on the lower carbon. On
account of the cooling between alternations, the mean temperature falls
below the vaporizing point of carbon, thus accounting for the lower
efficiency of the alternating current arc.
[Illustration: MAXIM DYNAMO.
This dynamo is in the collection of the Smithsonian Institution.]
For this reason all these systems used direct current and the 10 ampere
ultimately displaced the 20 ampere system. The 10 ampere circuit
was later standardized at 9.6 amperes, 50 volts per lamp. The lamp
therefore consumed 480 watts giving an efficiency of about 15 lumens
per watt. This lamp gave an average of 575 candlepower (spherical) in
all directions, though it was called the 2000 cp (candlepower) arc as
under the best possible conditions it could give this candlepower in
one direction. Later a 6.6 ampere arc was developed. This was called
the “1200 cp” lamp and was not quite as efficient as the 9.6 ampere
lamp.
“SUB-DIVIDING THE ELECTRIC LIGHT”
While the arc lamp was being commercially established, it was at once
seen that it was too large a unit for household use. Many inventors
attacked the problem of making a smaller unit, or, as it was called,
“sub-dividing the electric light.” In the United States there were four
men prominent in this work: William E. Sawyer, Moses G. Farmer, Hiram
S. Maxim and Thomas A. Edison. These men did not make smaller arc lamps
but all attempted to make an incandescent lamp that would operate on
the arc circuits.
[Illustration: SAWYER’S INCANDESCENT LAMP, 1878.
This had a graphite burner operating in nitrogen gas.]
[Illustration: FARMER’S INCANDESCENT LAMP, 1878.
The graphite burner operated in nitrogen gas. This lamp is in the
collection of the Smithsonian Institution.]
Sawyer made several lamps in the years 1878–79 along the lines of the
Russian scientists. All his lamps had a thick carbon burner operating
in nitrogen gas. They had a long glass tube closed at one end and the
other cemented to a brass base through which the gas was put in. Heavy
fluted wires connected the burner with the base to radiate the heat,
in order to keep the joint in the base cool. The burner was renewable
by opening the cemented joint. Farmer’s lamp consisted of a pair of
heavy copper rods mounted on a rubber cork, between which a graphite
rod was mounted. This was inserted in a glass bulb and operated in
nitrogen gas. Maxim made a lamp having a carbon burner operating in a
rarefied hydrocarbon vapor. He also made a lamp consisting of a sheet
of platinum operating in air.
EDISON’S INVENTION OF A PRACTICAL INCANDESCENT LAMP
Edison began the study of the problem in the spring of 1878. He had a
well-equipped laboratory at Menlo Park, New Jersey, with several able
assistants and a number of workmen, about a hundred people all told.
He had made a number of well-known inventions, among which were the
quadruplex telegraph whereby four messages could be sent simultaneously
over one wire, the carbon telephone transmitter without which Bell’s
telephone receiver would have been impracticable, and the phonograph.
All of these are in use today, so Edison was eminently fitted to attack
the problem.
[Illustration: MAXIM’S INCANDESCENT LAMP, 1878.
The carbon burner operated in a rarefied hydrocarbon vapor. This lamp
is in the collection of the Smithsonian Institution.]
Edison’s first experiments were to confirm the failures of other
experimenters. Convinced of the seeming impossibility of carbon, he
turned his attention to platinum as a light giving element. Realizing
the importance of operating platinum close to its melting temperature,
he designed a lamp which had a thermostatic arrangement so that
the burner would be automatically short circuited the moment its
temperature became dangerously close to melting. The burner consisted
of a double helix of platinum wire within which was a rod. When the
temperature of the platinum became too high, the rod in expanding
would short circuit the platinum. The platinum cooled at once, the
rod contracted opening the short circuit and allowing current to flow
through the burner again. His first incandescent lamp patent covered
this lamp. His next patent covered a similar lamp with an improved
thermostat consisting of an expanding diaphragm. Both of these lamps
were designed for use on series circuits.
[Illustration: EDISON’S FIRST EXPERIMENTAL LAMP, 1878.
The burner was a coil of platinum wire which was protected from
operating at too high a temperature by a thermostat.]
The only system of distributing electricity, known at that time, was
the series system. In this system current generated in the dynamo
armature flowed through the field coils, out to one lamp after another
over a wire, and then back to the dynamo. There were no means by which
one lamp could be turned on and off without doing the same with all the
others on the circuit. Edison realized that while this was satisfactory
for street lighting where arcs were generally used, it never would
be commercial for household lighting. He therefore decided that a
practical incandescent electric lighting system must be patterned
after gas lighting with which it would compete. He therefore made
an intensive study of gas distribution and reasoned that a constant
pressure electrical system could be made similar to that of gas.
The first problem was therefore to design a dynamo that would give a
constant pressure instead of constant current. He therefore reasoned
that the internal resistance of the armature must be very low or the
voltage would fall as current was taken from the dynamo. Scientists
had shown that the most economical use of electricity from a primary
battery was where the external resistance of the load was the same as
the internal resistance of the battery, or in other words, 50 per cent
was the maximum possible efficiency.
[Illustration: DIAGRAM OF CONSTANT CURRENT SERIES SYSTEM.
This, in 1878, was the only method of distributing electric current.]
[Illustration: DIAGRAM OF EDISON’S MULTIPLE SYSTEM, 1879.
Edison invented the multiple system of distributing electric current,
now universally used.]
When Edison proposed a very low resistance armature so that the dynamo
would have an efficiency of 90 per cent at full load, he was ridiculed.
Nevertheless he went ahead and made one which attained this. The
armature consisted of drum-wound insulated copper rods, the armature
core having circular sheets of iron with paper between to reduce the
eddy currents. There were two vertical fields above and connected in
shunt with the armature. It generated electricity at about a hundred
volts constant pressure and could supply current up to about 60
amperes at this pressure. It therefore had a capacity, in the present
terminology, of about 6 kilowatts (or 8 horsepower).
[Illustration: EDISON DYNAMO, 1879.
Edison made a dynamo that was 90 per cent efficient which scientists
said was impossible. This dynamo is in the collection of the
Smithsonian Institution and was one of the machines on the steamship
Columbia, the first commercial installation of the Edison lamp.]
A multiple system of distribution would make each lamp independent of
every other and with a dynamo made for such a system, the next thing
was to design a lamp for it. Having a pressure of about a hundred volts
to contend with, the lamp, in order to take a small amount of current,
must, to comply with Ohm’s law, have a high resistance. He therefore
wound many feet of fine platinum wire on a spool of pipe clay and
made his first high resistance lamp. He used his diaphragm thermostat
to protect the platinum from melting, and, as now seems obvious but
was not to all so-called electricians at that time, the thermostat
was arranged to open circuit instead of short circuit the burner when
it became too hot. This lamp apparently solved the problem, and, in
order to protect the platinum from the oxygen of the air, he coated
it with oxide of zirconium. Unfortunately zirconia, while an insulator
at ordinary temperatures, becomes, as is now known, a conductor of
electricity when heated, so that the lamp short circuited itself when
it was lighted.
[Illustration: EDISON’S HIGH RESISTANCE PLATINUM LAMP, 1879.
This lamp had a high resistance burner, necessary for the multiple
system.]
[Illustration: EDISON’S HIGH RESISTANCE PLATINUM IN VACUUM LAMP, 1879.
This experimental lamp led to the invention of the successful carbon
filament lamp.]
During his experiments he had found that platinum became exceedingly
hard after it had been heated several times to incandescence by current
flowing through it. This apparently raised its melting temperature so
he was able to increase the operating temperature and therefore greatly
increase the candlepower of his lamps after they had been heated a few
times. Examination of the platinum under a microscope showed it to be
much less porous after heating, so he reasoned that gases were occluded
throughout the platinum and were driven out by the heat. This led him
to make a lamp with a platinum wire to operate in vacuum, as he thought
that more of the occluded gases would come out under such circumstances.
[Illustration: EDISON’S CARBON LAMP OF OCTOBER 21, 1879.
This experimental lamp, having a high resistance carbon filament
operating in a high vacuum maintained by an all-glass globe, was the
keystone of Edison’s successful incandescent lighting system. All
incandescent lamps made today embody the basic features of this lamp.
This replica is in the Smithsonian Institution exhibit of Edison lamps.
The original was destroyed.]
These lamps were expensive to make, and, knowing that he could get the
requisite high resistance at much less cost from a long and slender
piece of carbon, he thought he might be able to make the carbon last
in the high vacuum he had been able to obtain from the newly invented
Geissler and Sprengel mercury air pumps. After several trials he
finally was able to carbonize a piece of ordinary sewing thread. This
he mounted in a one-piece all glass globe, all joints fused by melting
the glass together, which he considered was essential in order to
maintain the high vacuum. Platinum wires were fused in the glass to
connect the carbonized thread inside the bulb with the circuit outside
as platinum has the same coefficient of expansion as glass and hence
maintains an airtight joint. He reasoned that there would be occluded
gases in the carbonized thread which would immediately burn up if the
slightest trace of oxygen were present, so he heated the lamp while it
was still on the exhaust pump after a high degree of vacuum had been
obtained. This was accomplished by passing a small amount of current
through the “filament,” as he called it, gently heating it. Immediately
the gases started coming out, and it took eight hours more on the pump
before they stopped. The lamp was then sealed and ready for trial.
[Illustration: DEMONSTRATION OF EDISON’S INCANDESCENT LIGHTING SYSTEM.
Showing view of Menlo Park Laboratory Buildings, 1880.]
On October 21, 1879, current was turned into the lamp and it lasted
forty-five hours before it failed. A patent was applied for on November
4th of that year and granted January 27, 1880. All incandescent lamps
made today embody the basic features of this lamp. Edison immediately
began a searching investigation of the best material for a filament and
soon found that carbonized paper gave several hundred hours life. This
made it commercially possible, so in December, 1879, it was decided
that a public demonstration of his incandescent lighting system should
be made. Wires were run to several houses in Menlo Park, N. J., and
lamps were also mounted on poles, lighting the country roads in the
neighborhood. An article appeared in the New York Herald on Sunday,
December 21, 1879, describing Edison’s invention and telling of the
public demonstration to be given during the Christmas holidays. This
occupied the entire first page of the paper, and created such a furor
that the Pennsylvania Railroad had to run special trains to Menlo
Park to accommodate the crowds. The first commercially successful
installation of the Edison incandescent lamps and lighting system was
made on the steamship Columbia, which started May 2, 1880, on a voyage
around Cape Horn to San Francisco, Calif.
The carbonized paper filament of the first commercial incandescent lamp
was quite fragile. Early in 1880 carbonized bamboo was found to be not
only sturdy but made an even better filament than paper. The shape of
the bulb was also changed from round to pear shape, being blown from
one inch tubing. Later the bulbs were blown directly from molten glass.
[Illustration: DYNAMO ROOM, S. S. COLUMBIA.
The first commercial installation of the Edison Lamp, started May 2,
1880. One of these original dynamos is on exhibit at the Smithsonian
Institution.]
As it was inconvenient to connect the wires to the binding posts of
a new lamp every time a burned out lamp had to be replaced, a base
and socket for it were developed. The earliest form of base consisted
simply of bending the two wires of the lamp back on the neck of the
bulb and holding them in place by wrapping string around the neck. The
socket consisted of two pieces of sheet copper in a hollow piece of
wood. The lamp was inserted in this, the two-wire terminals of the lamp
making contact with the two-sheet copper terminals of the socket, the
lamp being rigidly held in the socket by a thumb screw which forced
the socket terminals tight against the neck of the bulb.
[Illustration: ORIGINAL SOCKET FOR INCANDESCENT LAMPS, 1880.]
[Illustration: WIRE TERMINAL BASE LAMP, 1880.
This crude form of lamp base fitted the original form of lamp socket
pictured above. This lamp is in the exhibit of Edison lamps in the
Smithsonian Institution.]
This crude arrangement was changed in the latter part of 1880 to a
screw shell and a ring for the base terminals, wood being used for
insulation. The socket was correspondingly changed. This was a very
bulky affair, so the base was changed to a cone-shaped ring and a
screw shell for terminals. Wood was used for insulation, which a short
time after was changed to plaster of Paris as this was also used to
fasten the base to the bulb. It was soon found that the tension created
between the two terminals of the base when the lamp was firmly screwed
in the socket often caused the plaster base to pull apart, so the shape
of the base was again changed early in 1881, to the form in use today.
An improved method of connecting the ends of the filament to the
leading-in wires was adopted early in 1881. Formerly this was
accomplished by a delicate clamp having a bolt and nut. The improvement
consisted of copper plating the filament to the leading-in wire.
[Illustration: ORIGINAL SCREW BASE LAMP, 1880.
This first screw base, consisting of a screw shell and ring for
terminals with wood for insulation, was a very bulky affair. This lamp
is in the exhibit of Edison lamps in the Smithsonian Institution.]
[Illustration: IMPROVED SCREW BASE LAMP, 1881.
The terminals of this base consisted of a cone shaped ring and a screw
shell. At first wood was used for insulation, later plaster of paris
which was also used to fasten the base to the bulb. This lamp is in the
exhibit of Edison lamps in the Smithsonian Institution.]
In the early part of the year 1881 the lamps were made “eight to
the horsepower.” Each lamp, therefore, consumed a little less than
100 watts, and was designed to give 16 candlepower in a horizontal
direction. The average candlepower (spherical) in all directions was
about 77 per cent of this, hence as the modern term “lumen” is 12.57
spherical candlepower, these lamps had an initial efficiency of about
1.7 lumens per watt. The lamps blackened considerably during their life
so that just before they burned out their candlepower was less than
half that when new. Thus their mean efficiency throughout life was
about 1.1 l-p-w (lumens per watt). These figures are interesting in
comparison with the modern 100-watt gas-filled tungsten-filament lamp
which has an initial efficiency of 12.9, and a mean efficiency of 11.8,
l-p-w. In other words the equivalent (wattage) size of modern lamp
gives over seven times when new, and eleven times on the average, as
much light for the same energy consumption as Edison’s first commercial
lamp. In the latter part of 1881 the efficiency was changed to “ten
lamps per horsepower,” equivalent to 2¼ l-p-w initially. Two sizes of
lamps were made: 16 cp for use on 110-volt circuits and 8 cp for use
either direct on 55 volts or two in series on 110-volt circuits.
[Illustration: FINAL FORM OF SCREW BASE, 1881.
With plaster of paris, the previous form of base was apt to pull apart
when the lamp was firmly screwed into the socket. The form of the base
was therefore changed to that shown, which overcame these difficulties,
and which has been used ever since. The lamp shown was standard for
three years and is in the exhibit of Edison lamps in the Smithsonian
Institution.]
EDISON’S THREE-WIRE SYSTEM
The distance at which current can be economically delivered at 110
volts pressure is limited, as will be seen from a study of Ohm’s law.
The loss of power in the distributing wires is proportional to the
square of the current flowing. If the voltage be doubled, the amount
of current is halved, for a given amount of electric power delivered,
so that the size of the distributing wires can then be reduced to
one-quarter for a given loss in them. At that time (1881) it was
impossible to make 220-volt lamps, and though they are now available,
their use is uneconomical, as their efficiency is much poorer than that
of 110-volt incandescent lamps.
Edison invented a distributing system that had two 110-volt circuits,
with one wire called the neutral, common to both circuits so that the
pressure on the two outside wires was 220 volts. The neutral wire had
only to be large enough to carry the difference between the currents
flowing in the two circuits. As the load could be so arranged that it
would be approximately equal at all times on both circuits, the neutral
wire could be relatively small in size. Thus the three-wire system
resulted in a saving of 60 per cent in copper over the two-wire system
or, for the same amount of copper, the distance that current could be
delivered was more than doubled.
[Illustration: DIAGRAM OF EDISON’S THREE-WIRE SYSTEM, 1881.
This system reduced the cost of copper in the multiple distributing
system 60 per cent.]
DEVELOPMENT OF THE ALTERNATING CURRENT CONSTANT POTENTIAL SYSTEM
The distance that current can be economically distributed, as has
been shown, depends upon the voltage used. If, therefore, current
could be sent out at a high voltage and the pressure brought down to
that desired at the various points to which it is distributed, such
distribution could cover a much greater area. Lucien Gaulard was a
French inventor and was backed by an Englishman named John D. Gibbs.
About 1882 they patented a series alternating-current system of
distribution. They had invented what is now called a transformer which
consisted of two separate coils of wire mounted on an iron core. All
the primary coils were connected in series, which, when current went
through them, induced a current in the secondary coils. Lamps were
connected in multiple on each of the secondary coils. An American
patent was applied for on the transformer, but was refused on the basis
that “more current cannot be taken from it than is put in.” While
this is true if the word energy were used, the transformer can supply
a greater current at a lower voltage (or vice versa) than is put in,
the ratio being in proportion to the relative number of turns in the
primary and secondary coils. The transformer was treated with ridicule
and Gaulard died under distressing circumstances.
[Illustration: DIAGRAM OF STANLEY’S ALTERNATING CURRENT MULTIPLE
SYSTEM, 1885.
This system is now universally used for distributing electric current
long distances.]
Information regarding the transformer came to the attention of
William Stanley, an American, in the latter part of 1885. He made an
intensive study of the scheme, and developed a transformer in which
the primary coil was connected in multiple on a constant potential
alternating-current high-voltage system. From the secondary coil a
lower constant voltage was obtained. An experimental installation
was made at Great Barrington, Mass., in the early part of 1886, the
first commercial installation being made in Buffalo, New York, in the
latter part of the year. This scheme enabled current to be economically
distributed to much greater distances. The voltage of the high-tension
circuit has been gradually increased as the art has progressed from
about a thousand volts to over two hundred thousand volts pressure in a
recent installation in California, where electric power is transmitted
over two hundred miles.
INCANDESCENT LAMP DEVELOPMENTS, 1884–1894
In 1884 the ring of plaster around the top of the base was omitted; in
1886 an improvement was made by pasting the filament to the leading-in
wires with a carbon paste instead of the electro-plating method; and
in 1888 the length of the base was increased so that it had more
threads. Several concerns started making incandescent lamps, the
filaments being made by carbonizing various substances. “Parchmentized”
thread consisted of ordinary thread passed through sulphuric acid.
“Tamadine” was cellulose in the sheet form, punched out in the shape
of the filament. Squirted cellulose in the form of a thread was also
used. This was made by dissolving absorbent cotton in zinc chloride,
the resulting syrup being squirted through a die into alcohol which
hardened the thread thus formed. This thread was washed in water, dried
in the air and then cut to proper length and carbonized.
[Illustration: STANDARD EDISON LAMP, 1884.
The ring of plaster around the neck of previous lamps was omitted. This
lamp is in the exhibit of Edison lamps in the Smithsonian Institution.]
[Illustration: STANDARD EDISON LAMP, 1888.
The length of the base was increased so it had more threads. This lamp
is in the exhibit of Edison lamps in the Smithsonian Institution.]