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SMITHSONIAN MISCELLANEOUS COLLECTIONS
VOLUME 76, NUMBER 2

HISTORY OF ELECTRIC LIGHT

BY
HENRY SCHROEDER
Harrison, New Jersey

FOR THE INCREASE
AND DIFFVSION OF
KNOWLEDGE AMONG MEN

SMITHSONIAN
INSTITVTION
WASHINGTON 1846

(Publication 2717)

CITY OF WASHINGTON
PUBLISHED BY THE SMITHSONIAN INSTITUTION
AUGUST 15, 1923

The Lord Baltimore Press
BALTIMORE, MD., U. S. A.

CONTENTS

LIST OF ILLUSTRATIONS

Portion of the Electrical Exhibit in the United States National Museum.

Section devoted to the historical development of the electric light and dynamo.

FOREWORD

In the year 1884 a Section of Transportation was organized in the United States National Museum for the purpose of preparing and assembling educational exhibits of a few objects of railroad machinery which had been obtained both from the Centennial Exhibition held in Philadelphia in 1876 and still earlier as incidentals to ethnological collections, and to secure other collections relating to the railway industry.

From this beginning the section was expanded to include the whole field of engineering and is designated at present as the Divisions of Mineral and Mechanical Technology. The growth and enlargement of the collections has been particularly marked in the fields of mining and mineral industries; mechanical engineering, especially pertaining to the steam engine, internal combustion engine and locomotive; naval architecture, and electrical engineering, particularly the development of the telegraph, telephone and the electric light.

In the acquisition of objects visualizing the history of electric light the Museum has been rather fortunate, particularly as regards the developments in the United States. Thus mention may be made of the original Patent Office models of the more important dynamos, arc lights and incandescent lights, together with original commercial apparatus after these models; a unit of the equipment used in the first commercially successful installation on land of an incandescent lighting system, presented by Joseph E. Hinds in whose engraving establishment in New York City the installation was made in 1881; and a large series of incandescent lights, mainly originals, visualizing chronologically the developments of the Edison light from its inception, presented at intervals since the year 1898 by the General Electric Company.

The object of all collections in the Divisions is to visualize broadly the steps by which advances have been made in each field of engineering; to show the layman the fundamental and general principles which are the basis for the developments; and to familiarize the engineer with branches of engineering other than his own. Normally when a subject is completely covered by a collection of objects, a paper is prepared and published describing the collection and the story it portrays. In the present instance, however, on account of the uncertainty of the time of completing the collection, if it is possible ever to bring this about, it was thought advisable to publish Mr. Schroeder’s paper which draws upon the Museum collection as completely as possible.

Carl W. Mitman,
Curator, Divisions of Mineral and
Mechanical Technology,
U. S. National Museum.

CHRONOLOGY OF ELECTRIC LIGHT

1800—Allesandro Volta demonstrated his discovery that electricity can be generated by chemical means. The Volt, the unit of electric pressure, is named in his honor for this discovery of the electric battery.

1802—Sir Humphry Davy demonstrated that electric current can heat carbon and strips of metal to incandescence and give light.

1809—Sir Humphry Davy demonstrated that current will give a brilliant flame between the ends of two carbon pencils which are first allowed to touch each other and then pulled apart. This light he called the “arc” on account of its arch shape.

1820—André Marie Ampère discovered that current flowing through a coiled wire gives it the properties of a magnet. The Ampere, the unit of flow of electric current, is named in his honor for this discovery.

1825—Georg Simon Ohm discovered the relation between the voltage, ampereage and resistance in an electric circuit, which is called Ohm’s Law. The Ohm, the unit of electric resistance, is named in his honor for this discovery.

1831—Michael Faraday discovered that electricity can be generated by moving a wire in the neighborhood of a magnet, the principle of the dynamo.

1840—Sir William Robert Grove demonstrated his experimental incandescent lamp in which platinum is made incandescent by current flowing through it.

1841—Frederick De Moleyns obtained the first patent on an incandescent lamp. The burner was powdered charcoal operating in an exhausted glass globe.

1845—Thomas Wright obtained the first patent on an arc light.

1845—J. W. Starr invented an incandescent lamp consisting of a carbon pencil operating in the vacuum above a column of mercury.

1856—Joseph Lacassagne and Henry Thiers invented the “differential” method of control of the arc which was universally used twenty years later when the arc lamp was commercially established.

1862—The first commercial installation of an electric light. An arc light was put in a lighthouse in England.

1866—Sir Charles Wheatstone invented the “self-excited” dynamo, now universally used.

1872—Lodyguine invented an incandescent lamp having a graphite burner operating in nitrogen gas.

1876—Paul Jablochkoff invented the “electric candle,” an arc light commercially used for lighting the boulevards in Paris.

1877–8—Arc light systems commercially established in the United States by William Wallace and Prof. Moses Farmer, Edward Weston, Charles F. Brush and Prof. Elihu Thomson and Edwin J. Houston.

1879—Thomas Alva Edison invented an incandescent lamp consisting of a high resistance carbon filament operating in a high vacuum maintained by an all glass globe. These principles are used in all incandescent lamps made today. He also invented a completely new system of distributing electricity at constant pressure, now universally used.

1882—Lucien Goulard and John D. Gibbs invented a series alternating current system of distributing electric current. This has not been commercially used.

1886—William Stanley invented a constant pressure alternating current system of distribution. This is universally used where current is to be distributed long distances.

1893—Louis B. Marks invented the enclosed carbon arc lamp.

1898—Bremer’s invention of the flame arc lamp, having carbons impregnated with various salts, commercially established.

1900—Dr. Walther Nernst’s invention of the Nernst lamp commercially established. The burner consisted of various oxides, such as zirconia, which operated in the open air.

1901—Dr. Peter Cooper Hewitt’s invention of the mercury arc light commercially established.

1902—The magnetite arc lamp was developed by C. A. B. Halvorson, Jr. This has a new method of control of the arc. The negative electrode consists of a mixture of magnetite and other substances packed in an iron tube.

1904—D. McFarlan Moore’s invention of the Moore vacuum tube light commercially established. This consisted of a long tube, made in lengths up to 200 feet, from which the air had been exhausted to about a thousandth of an atmosphere. High voltage current passing through this rarefied atmosphere caused it to glow. Rarefied carbon dioxide gas was later used.

1905—Dr. Auer von Welsbach’s invention of the osmium incandescent lamp commercially established, but only on a small scale in Europe. The metal osmium, used for the filament which operated in vacuum, is rarer and more expensive than platinum.

1905—Dr. Willis R. Whitney’s invention of the Gem incandescent lamp commercially established. The carbon filament had been heated to a very high temperature in an electric resistance furnace invented by him. The lamp was 25 per cent more efficient than the regular carbon lamp.

1906—Dr. Werner von Bolton’s invention of the tantalum incandescent lamp commercially established.

1907—Alexander Just and Franz Hanaman’s invention of the tungsten filament incandescent lamp commercially established.

1911—Dr. William D. Coolidge’s invention of drawn tungsten wire commercially established.

1913—Dr. Irving Langmuir’s invention of the gas-filled tungsten filament incandescent lamp commercially established.

HISTORY OF ELECTRIC LIGHT

By HENRY SCHROEDER,
HARRISON, NEW JERSEY.

EARLY RECORDS OF ELECTRICITY AND MAGNETISM

About twenty-five centuries ago, Thales, a Greek philosopher, recorded the fact that if amber is rubbed it will attract light objects. The Greeks called amber “elektron,” from which we get the word “electricity.” About two hundred and fifty years later, Aristotle, another Greek philosopher, mentioned that the lodestone would attract iron. Lodestone is an iron ore (Fe₃O₄), having magnetic qualities and is now called magnetite. The word “magnet” comes from the fact that the best specimens of lodestones came from Magnesia, a city in Asia Minor. Plutarch, a Greek biographer, wrote about 100 A. D., that iron is sometimes attracted and at other times repelled by a lodestone. This indicates that the piece of iron was magnetised by the lodestone.

In 1180, Alexander Neckham, an English Monk, described the compass, which probably had been invented by sailors of the northern countries of Europe, although its invention has been credited to the Chinese. Early compasses probably consisted of an iron needle, magnetised by a lodestone, mounted on a piece of wood floating in water. The word lodestone or “leading stone” comes from the fact that it would point towards the north if suspended like a compass.

William Gilbert, physician to Queen Elizabeth of England, wrote a book about the year 1600 giving all the information then known on the subject. He also described his experiments, showing, among other things, the existence of magnetic lines of force and of north and south poles in a magnet. Robert Norman had discovered a few years previously that a compass needle mounted on a horizontal axis would dip downward. Gilbert cut a large lodestone into a sphere, and observed that the needle did not dip at the equator of this sphere, the dip increasing to 90 degrees as the poles were approached. From this he deduced that the earth was a magnet with the magnetic north pole at the geographic north pole. It has since been determined that these two poles do not coincide. Gilbert suggested the use of the dipping needle to determine latitude. He also discovered that other substances, beside amber, would attract light objects if rubbed.

MACHINES GENERATING ELECTRICITY BY FRICTION

Otto Von Guericke was mayor of the city of Magdeburg as well as a philosopher. About 1650 he made a machine consisting of a ball of sulphur mounted on a shaft which could be rotated. Electricity was generated when the hand was pressed against the globe as it rotated. He also discovered that electricity could be conducted away from the globe by a chain and would appear at the other end of the chain. Von Guericke also invented the vacuum air pump. In 1709, Francis Hawksbee, an Englishman, made a similar machine, using a hollow glass globe which could be exhausted. The exhausted globe when rotated at high speed and rubbed by hand would produce a glowing light. This “electric light” as it was called, created great excitement when it was shown before the Royal Society, a gathering of scientists, in London.

Otto Von Guericke’s Electric Machine, 1650.

A ball of sulphur was rotated, electricity being generated when it rubbed against the hand.

Stephen Gray, twenty years later, showed the Royal Society that electricity could be conducted about a thousand feet by a hemp thread, supported by silk threads. If metal supports were used, this could not be done. Charles du Fay, a Frenchman, repeated Gray’s experiments, and showed in 1733 that the substances which were insulators, and which Gilbert had discovered, would become electrified if rubbed. Those substances which Gilbert could not electrify were conductors of electricity.

THE LEYDEN JAR

The thought came to Von Kleist, Bishop of Pomerania, Germany, about 1745, that electricity could be stored. The frictional machines generated so small an amount of electricity (though, as is now known, at a very high pressure—several thousand volts) that he thought he could increase the quantity by storing it. Knowing that glass was an insulator and water a conductor, he filled a glass bottle partly full of water with a nail in the cork to connect the machine with the water. Holding the bottle in one hand and turning the machine with the other for a few minutes, he then disconnected the bottle from the machine. When he touched the nail with his other hand he received a shock which nearly stunned him. This was called the Leyden jar, the forerunner of the present condenser. It received its name from the fact that its discovery was also made a short time after by experimenters in the University of Leyden. Further experiments showed that the hand holding the bottle was as essential as the water inside, so these were substituted by tin foil coatings inside and outside the bottle.

Benjamin Franklin, American statesman, scientist and printer, made numerous experiments with the Leyden jar. He connected several jars in parallel, as he called it, which gave a discharge strong enough to kill a turkey. He also connected the jars in series, or “in cascade” as he called it, thus establishing the principle of parallel and series connections. Noticing the similarity between the electric spark and lightning, Franklin in 1752, performed his famous kite experiment. Flying a kite in a thunderstorm, he drew electricity from the clouds to charge Leyden jars, which were later discharged, proving that lightning and electricity were the same. This led him to invent the lightning rod.

ELECTRICITY GENERATED BY CHEMICAL MEANS

Luigi Galvani was an Italian scientist. About 1785, so the story goes, his wife was in delicate health, and some frog legs were being skinned to make her a nourishing soup. An assistant holding the legs with a metal clamp and cutting the skin with a scalpel, happened to let the clamp and scalpel touch each other. To his amazement the frog legs twitched. Galvani repeated the experiment many times by touching the nerve with a metal rod and the muscle with a different metal rod and allowing the rods to touch, and propounded the theory of animal electricity in a paper he published in 1791.

Allesandro Volta, a professor of physics in the University of Pavia, Italy, read about Galvani’s work and repeated his experiments. He found that the extent of the movement of the frog legs depended on the metals used for the rods, and thus believed that the electric charge was produced by the contact of dissimilar metals with the moisture in the muscles. To prove his point he made a pile of silver and zinc discs with cloths, wet with salt water, between them. This was in 1799, and he described his pile in March, 1800, in a letter to the Royal Society in London.

Voltaic Pile, 1799.

Volta discovered that electricity could be generated by chemical means and made a pile of silver and zinc discs with cloths, wet with salt water, between them. This was the forerunner of the present-day dry battery. Photograph courtesy Prof. Chas. F. Chandler Museum, Columbia University, New York.

This was an epoch-making discovery as it was the forerunner of the present-day primary battery. Volta soon found that the generation of electricity became weaker as the cloths became dry, so to overcome this he made his “crown of cups.” This consisted of a series of cups containing salt water in which strips of silver and zinc were dipped. Each strip of silver in one cup was connected to the zinc strip in the next cup, the end strips of silver and zinc being terminals of the battery. This was the first time that a continuous supply of electricity in reasonable quantities was made available, so the Volt, the unit of electrical pressure was named in his honor. It was later shown that the chemical affinity of one of the metals in the liquid was converted into electric energy. The chemical action of Volta’s battery is that the salt water attacks the zinc when the circuit is closed forming zinc chloride, caustic soda and hydrogen gas. The chemical equation is:

Zn + 2NaCl + 2H₂O = ZnCl₂ + 2NaOH + H₂

IMPROVEMENT OF VOLTA’S BATTERY

It was early suggested that sheets of silver and zinc be soldered together back to back and that a trough be divided into cells by these bimetal sheets being put into grooves cut in the sides and bottom of the trough. This is the reason why one unit of a battery is called a “cell.” It was soon found that a more powerful cell could be made if copper, zinc and dilute sulphuric acid were used. The zinc is dissolved by the acid forming zinc sulphate and hydrogen gas, thus:

Zn + H₂SO₄ = ZnSO₄ + H₂

The hydrogen gas appears as bubbles on the copper and reduces the open circuit voltage (about 0.8 volt per cell) as current is taken from the battery. This is called “polarization.” Owing to minute impurities in the zinc, it is attacked by the acid even when no current is taken from the battery, the impurities forming with the zinc a short circuited local cell. This is called “local action,” and this difficulty was at first overcome by removing the zinc from the acid when the battery was not in use.

DAVY’S DISCOVERIES

Sir Humphry Davy was a well-known English chemist, and with the aid of powerful batteries constructed for the Royal Institution in London, he made numerous experiments on the chemical effects of electricity. He decomposed a number of substances and discovered the elements boron, potassium and sodium. He heated strips of various metals to incandescence by passing current through them, and showed that platinum would stay incandescent for some time without oxidizing. This was about 1802.

In the early frictional machines, the presence of electricity was shown by the fact that sparks could be obtained. Similarly the breaking of the circuit of a battery would give a spark. Davy, about 1809, demonstrated that this spark could be maintained for a long time with the large battery of 2000 cells he had had constructed. Using two sticks of charcoal connected by wires to the terminals of this very powerful battery, he demonstrated before the Royal Society the light produced by touching the sticks together and then holding them apart horizontally about three inches. The brilliant flame obtained he called an “arc” because of its arch shape, the heated gases, rising, assuming this form. Davy was given the degree of LL. D. for his distinguished research work, and was knighted on the eve of his marriage, April 11, 1812.

RESEARCHES OF OERSTED, AMPÈRE, SCHWEIGGER AND STURGEON

Hans Christian Oersted was a professor of physics at the University of Copenhagen in Denmark. One day in 1819, while addressing his students, he happened to hold a wire, through which current was flowing, over a large compass. To his surprise he saw the compass was deflected from its true position. He promptly made a number of experiments and discovered that by reversing the current the compass was deflected in the opposite direction. Oersted announced his discovery in 1820.

André Marie Ampère was a professor of mathematics in the Ecole Polytechnic in Paris. Hearing of Oersted’s discovery, he immediately made some experiments and made the further discovery in 1820 that if the wire is coiled and current passed through it, the coil had all the properties of a magnet.

These two discoveries led to the invention of Schweigger in 1820, of the galvanometer (or “multiplier” as it was then called), a very sensitive instrument for measuring electric currents. It consisted of a delicate compass needle suspended in a coil of many turns of wire. Current in the coil deflected the needle, the direction and amount of deflection indicating the direction and strength of the current. Ampère further made the discovery that currents in opposite directions repel and in the same directions attract each other. He also gave a rule for determining the direction of the current by the deflection of the compass needle. He developed the theory that magnetism is caused by electricity flowing around the circumference of the body magnetised. The Ampere, the unit of flow of electric current, was named in honor of his discoveries.

In 1825 it was shown by Sturgeon that if a bar of iron were placed in the coil, its magnetic strength would be very greatly increased, which he called an electro-magnet.

OHM’S LAW

Georg Simon Ohm was born in Bavaria, the oldest son of a poor blacksmith. With the aid of friends he went to college and became a teacher. It had been shown that the rate of transfer of heat from one end to the other of a metal bar is proportional to the difference of temperature between the ends. About 1825, Ohm, by analogy and experiment, found that the current in a conductor is proportional to the difference of electric pressure (voltage) between its ends. He further showed that with a given difference of voltage, the current in different conductors is inversely proportional to the resistance of the conductor. Ohm therefore propounded the law that the current flowing in a circuit is equal to the voltage on that circuit divided by the resistance of the circuit. In honor of this discovery, the unit of electrical resistance is called the Ohm. This law is usually expressed as:

C = E/R

“C” meaning current (in amperes), “E” meaning electromotive force or voltage (in volts) and “R” meaning resistance (in ohms).

This is one of the fundamental laws of electricity and if thoroughly understood, will solve many electrical problems. Thus, if any two of the above units are known, the third can be determined. Examples: An incandescent lamp on a 120-volt circuit consumes 0.4 ampere, hence its resistance under such conditions is 300 ohms. Several trolley cars at the end of a line take 100 amperes to run them and the resistance of the overhead wire from the power house to the trolley cars is half an ohm; the drop in voltage on the line between the power house and trolley cars is therefore 50 volts, so that if the voltage at the power house were 600, it would be 550 volts at the end of the line.

Critics derided Ohm’s law so that he was forced out of his position as teacher in the High School in Cologne. Finally after ten years Ohm began to find supporters and in 1841 his law was publicly recognized by the Royal Society of London which presented him with the Copley medal.

INVENTION OF THE DYNAMO

Michael Faraday was an English scientist. Born of parents in poor circumstances, he became a bookbinder and studied books on electricity and chemistry. He finally obtained a position as laboratory assistant to Sir Humphry Davy helping him with his lectures and experiments. He also made a number of experiments himself and succeeded in liquifying chlorine gas for which he was elected to a Fellowship in the Royal Institution in 1824. Following up Oersted’s and Ampère’s work, he endeavored to find the relation between electricity and magnetism. Finally on Oct. 17, 1831, he made the experiment of moving a permanent bar magnet in and out of a coil of wire connected to a galvanometer. This generated electricity in the coil which deflected the galvanometer needle. A few days after, Oct. 28, 1831, he mounted a copper disk on a shaft so that the disk could be rotated between the poles of a permanent horseshoe magnet. The shaft and edge of the disk were connected by brushes and wires to a galvanometer, the needle of which was deflected as the disk was rotated. A paper on his invention was read before the Royal Society on November 24, 1831, which appeared in printed form in January, 1832.

Faraday’s Dynamo, 1831.

Faraday discovered that electricity could be generated by means of a permanent magnet. This principle is used in all dynamos.

Faraday did not develop his invention any further, being satisfied, as in all his work, in pure research. His was a notable invention but it remained for others to make it practicable. Hippolyte Pixii, a Frenchman, made a dynamo in 1832 consisting of a permanent horseshoe magnet which could be rotated between two wire bobbins mounted on a soft iron core. The wires from the bobbins were connected to a pair of brushes touching a commutator mounted on the shaft holding the magnet, and other brushes carried the current from the commutator so that the alternating current generated was rectified into direct current.

Pixii’s Dynamo, 1832.

Pixii made an improvement by rotating a permanent magnet in the neighborhood of coils of wire mounted on a soft iron core. A commutator rectified the alternating current generated into direct current. This dynamo is in the collection of the Smithsonian Institution.

E. M. Clarke, an Englishman made, in 1834, another dynamo in which the bobbins rotated alongside of the poles of a permanent horseshoe magnet. He also made a commutator so that the machine produced direct current. None of these machines gave more than feeble current at low pressure. The large primary batteries that had been made were much more powerful, although expensive to operate. It has been estimated that the cost of current from the 2000-cell battery to operate the demonstration of the arc light by Davy, was six dollars a minute. At present retail rates for electricity sold by lighting companies, six dollars would operate Davy’s arc light about 500 hours or 30,000 times as long.

DANIELL’S BATTERY

Daniell’s Cell, 1836.

Daniell invented a battery consisting of zinc, copper and copper sulphate. Later the porous cup was dispensed with, which was used to keep the sulphuric acid formed separate from the solution of copper sulphate, the two liquids then being kept apart by their difference in specific gravity. It was then called the Gravity Battery and for years was used in telegraphy.

It was soon discovered that if the zinc electrode were rubbed with mercury (amalgamated), the local action would practically cease, and if the hydrogen bubbles were removed, the operating voltage of the cell would be increased. John Frederic Daniell, an English chemist, invented a cell in 1836 to overcome these difficulties. His cell consisted of a glass jar containing a saturated solution of copper sulphate (CuSO₄). A copper cylinder, open at both ends and perforated with holes, was put into this solution. On the outside of the copper cylinder there was a copper ring, located below the surface of the solution, acting as a shelf to support crystals of copper sulphate. Inside the cylinder there was a porous earthenware jar containing dilute sulphuric acid and an amalgamated zinc rod. The two liquids were therefore kept apart but in contact with each other through the pores of the jar. The hydrogen gas given off by the action of the sulphuric acid on the zinc, combined with the dissolved copper sulphate, formed sulphuric acid and metallic copper. The latter was deposited on the copper cylinder which acted as the other electrode. Thus the copper sulphate acted as a depolarizer.

The chemical reactions in this cell are,

In inner porous jar: Zn + H₂SO₄ = ZnSO₄ + H₂
In outer glass jar: H₂ + CuSO₄ = H₂SO₄ + Cu

This cell had an open circuit voltage of a little over one volt. Later the porous cup was dispensed with, the two liquids being kept apart by the difference of their specific gravities. This was known as the Gravity cell, and for years was used in telegraphy.

Grove’s Cell, 1838.

This consisted of zinc, sulphuric acid, nitric acid and platinum. It made a very powerful battery. The nitric acid is called the depolarizer as it absorbs the hydrogen gas formed, thus improving the operating voltage.

GROVE’S BATTERY

Sir William Robert Grove, an English Judge and scientist, invented a cell in 1838 consisting of a platinum electrode in strong nitric acid in a porous earthenware jar. This jar was put in dilute sulphuric acid in a glass jar in which there was an amalgamated zinc plate for the other electrode. This had an open circuit voltage of about 1.9 volts. The porous jar was used to prevent the nitric acid from attacking the zinc. The nitric acid was used for the purpose of combining with the hydrogen gas set free by the action of the sulphuric acid on the zinc, and hence was the depolarizing agent. Hydrogen combining with nitric acid forms nitrous peroxide and water. Part of the nitrous peroxide is dissolved in the water, and the rest escapes as fumes which, however, are very suffocating.

The chemical equations of this cell are as follows:

In outer glass jar: Zn + H₂SO₄ = ZnSO₄ + H₂
In inner porous jar: H₂ + 2HNO₃ = N₂O₄ + 2H₂O

An interesting thing about Grove’s cell is that it was planned in accordance with a theory. Grove knew that the electrical energy of the zinc-sulphuric acid cell came from the chemical affinity of the two reagents, and if the hydrogen gas set free could be combined with oxygen (to form water—H₂O), such chemical affinity should increase the strength of the cell. As the hydrogen gas appears at the other electrode, the oxidizing agent should surround that electrode. Nitric acid was known at that time as one of the most powerful oxidizing liquids, but as it attacks copper, he used platinum for the other electrode. Thus he not only overcame the difficulty of polarization by the hydrogen gas, but also increased the voltage of the cell by the added chemical action of the combination of hydrogen and oxygen.

GROVE’S DEMONSTRATION OF INCANDESCENT LIGHTING

In 1840 Grove made an experimental lamp by attaching the ends of a coil of platinum wire to copper wires, the lower parts of which were well varnished for insulation. The platinum wire was covered by a glass tumbler, the open end set in a glass dish partly filled with water. This prevented draughts of air from cooling the incandescent platinum, and the small amount of oxygen of the air in the tumbler reduced the amount of oxidization of the platinum that would otherwise occur. With current supplied by a large number of cells of his battery, he lighted the auditorium of the Royal Institution with these lamps during one of the lectures he gave. This lamp gave only a feeble light as there was danger of melting the platinum and platinum gives but little light unless operated close to its melting temperature. It also required a lot of current to operate it as the air tended to cool the incandescent platinum. The demonstration was only of scientific interest, the cost of current being much too great (estimated at several hundred dollars a kilowatt hour) to make it commercial.

GRENET BATTERY

It was discovered that chromic anhydride gives up oxygen easier than nitric acid and consequently if used would give a higher voltage than Grove’s nitric acid battery. It also has the advantage of a lesser tendency to attack zinc directly if it happens to come in contact with it. Grenet developed a cell having a liquid consisting of a mixture of potassium bichromate (K₂Cr₂O₇) and sulphuric acid. A porous cell was therefore not used to keep the two liquids apart. This had the advantage of reducing the internal resistance. The chemical reaction was:

K_{2}Cr_{2}O_{7} (potassium bichromate) + 7H_{2}SO_{4} (sulphuric acid) + 3Zn (zinc) = 3ZnSO₄ (zinc sulphate) + K₂SO₄ (potassium sulphate) + Cr₂ (SO₄)₃ (chromium sulphate) + 7H₂O (water).

In order to prevent the useless consumption of zinc on open circuit, the zinc was attached to a sliding rod and could be drawn up into the neck of the bottle-shaped jar containing the liquid.

Grove’s Incandescent Lamp, 1840.

Grove made an experimental lamp, using platinum for the burner which was protected from draughts of air by a glass tumbler.

DE MOLEYNS’ INCANDESCENT LAMP

Frederick De Moleyns, an Englishman, has the honor of having obtained the first patent on an incandescent lamp. This was in 1841 and his lamp was quite novel. It consisted of a spherical glass globe, in the upper part of which was a tube containing powdered charcoal. This tube was open at the bottom inside the globe and through it ran a platinum wire, the end below the tube being coiled. Another platinum wire coiled at its upper end came up through the lower part of the globe but did not quite touch the other platinum coil. The powdered charcoal filled the two coils of platinum wire and bridged the gap between. Current passing through this charcoal bridge heated it to incandescence. The air in the globe having been removed as far as was possible with the hand air pumps then available, the charcoal did not immediately burn up, the small amount consumed being replaced by the supply in the tube. The idea was ingenious but the lamp was impractical as the globe rapidly blackened from the evaporation of the incandescent charcoal.

De Moleyns’ Incandescent Lamp, 1841.

This consisted of two coils of platinum wire containing powdered charcoal operating in a vacuum. It is only of interest as the first incandescent lamp on which a patent (British) was granted.

EARLY DEVELOPMENTS OF THE ARC LAMP

It had been found that most of the light of the arc came from the tip of the positive electrode, and that the charcoal electrodes were rapidly consumed, the positive electrode about twice as fast as the negative. Mechanisms were designed to take care of this, together with devices to start the arc by allowing the electrodes to touch each other and then pulling them apart the proper distance. This distance varied from one-eighth to three-quarters of an inch.

In 1840 Bunsen, the German chemist who invented the bunsen burner, devised a process for making hard dense carbon pencils which lasted much longer than the charcoal previously used. The dense carbon from the inside of the retorts of gas making plants was ground up and mixed with molasses, moulded into shape and baked at a high temperature. Bunsen also, in 1843, cheapened Grove’s battery by substituting a hard carbon plate in place of the platinum electrode.

Wright’s Arc Lamp, 1845.

This lamp is also only of interest as the first arc lamp on which a patent (British) was granted. Four arcs played between the five carbon discs.

Thomas Wright, an Englishman, was the first to patent an arc lamp. This was in 1845, and the lamp was a hand regulated device consisting of five carbon disks normally touching each other and rotated by clockwork. Two of the disks could be drawn outward by thumb screws, which was to be done after the current was turned on thus establishing four arcs, one between each pair of disks. The next year, 1846, W. E. Staite, another Englishman, made an arc lamp having two vertical carbon pencils. The upper was stationary. The lower was movable and actuated by clockwork directed by ratchets which in turn were regulated by an electro-magnet controlled by the current flowing through the arc. Thus the lower carbon would be moved up or down as required.

Archereau, a Frenchman, made a very simple arc lamp in 1848. The upper carbon was fixed and the lower one was mounted on a piece of iron which could be drawn down into a coil of wire. The weight of the lower electrode was overbalanced by a counterweight, so that when no current was flowing the two carbons would touch. When current was turned on, it flowed through the two carbons and through the coil of wire (solenoid) which then became energized and pulled the lower carbon down, thus striking the arc. Two of these arc lamps were installed in Paris and caused considerable excitement. After a few weeks of unreliable operation, it was found that the cost of current from the batteries was much too great to continue their use commercially. The dynamo had not progressed far enough to permit its use.

Archereau’s Arc Lamp, 1848.

This simple arc was controlled by an electro-magnet, and two lamps were installed for street lighting in Paris, current being obtained from batteries.

JOULE’S LAW

Joule was an Englishman, and in 1842 began investigating the relation between mechanical energy and heat. He first showed that, by allowing a weight to drop from a considerable height and turn a paddle wheel in water, the temperature of the water would increase in relation to the work done in turning the wheel. It is now known that 778 foot-pounds (1 lb. falling 778 feet, 10 lbs. falling 77.8 feet or 778 lbs. falling one foot, etc.) is the mechanical equivalent of energy equal to raising one pound of water one degree Fahrenheit. The rate of energy (power) is the energy divided by a unit of time; thus one horsepower is 33,000 foot-pounds per minute. Joule next investigated the relation between heat and electric current. He made a device consisting of a vessel of water in which there were a thermometer and an insulated coil of wire having a considerable resistance. He found that an electric current heated the water, and making many combinations of the amount and length of time of current flowing and of the resistance of the wire, he deduced the law that the energy in an electric circuit is proportional to the square of the amount of current flowing multiplied by the length of time and multiplied by the resistance of the wire.

The rate of electrical energy (electric power) is therefore proportional to the square of current multiplied by the resistance. The electrical unit of power is now called the Watt, named in honor of James Watt, the Englishman, who made great improvements to the steam engine about a century ago. Thus, watts = C²R and substituting the value of R from Ohm’s law, C = E/R, we get

Watts = Volts × Amperes

The watt is a small unit of electric power, as can be seen from the fact that 746 watts are equal to one horsepower. The kilowatt, kilo being the Greek word for thousand, is 1000 watts.

This term is an important one in the electrical industry. For example, dynamos are rated in kilowatts, expressed as KW; the largest one made so far is 50,000 KW which is 66,666 horsepower. Edison’s first commercial dynamo had a capacity of 6 KW although the terms watts and kilowatts were not in use at that time. The ordinary sizes of incandescent lamps now used in the home are 25, 40 and 50 watts.

STARR’S INCANDESCENT LAMP

Starr’s Incandescent Lamp, 1845.

This consisted of a short carbon pencil operating in the vacuum above a column of mercury.

J. W. Starr, an American, of Cincinnati, Ohio, assisted financially by Peabody, the philanthropist, went to England where he obtained a patent in 1845 on the lamps he had invented, although the patent was taken out under the name of King, his attorney. One is of passing interest only. It consisted of a strip of platinum, the active length of which could be adjusted to fit the battery strength used, and was covered by a glass globe to protect it from draughts of air. The other, a carbon lamp, was the first real contribution to the art. It consisted of a rod of carbon operating in the vacuum above a column of mercury (Torrecellium vacuum) as in a barometer. A heavy platinum wire was sealed in the upper closed end of a large glass tube, and connected to the carbon rod by an iron clamp. The lower end of the carbon rod was fastened to another iron clamp, the two clamps being held in place and insulated from each other by a porcelain rod. Attached to the lower clamp was a long copper wire. Just below the lower clamp, the glass tube was narrowed down and had a length of more than 30 inches. The tube was then filled with mercury, the bottom of the tube being put into a vessel partly full of mercury. The mercury ran out of the enlarged upper part of the tube, coming to rest in the narrow part of the tube as in a barometer, so that the carbon rod was then in a vacuum. One lamp terminal was the platinum wire extending through the top of the tube, and the other was the mercury. Several of these lamps were put on exhibition in London, but were not a commercial success as they blackened very rapidly. Starr started his return trip to the United States the next year, but died on board the ship when he was but 25 years old.

OTHER EARLY INCANDESCENT LAMPS

Staite’s Incandescent Lamp, 1848.

The burner was of platinum and iridium.

Roberts’ Incandescent Lamp, 1852.

It had a graphite burner operating in vacuum.

In 1848 W. E. Staite, who two years previously had made an arc lamp, invented an incandescent lamp. This consisted of a platinum-iridium burner in the shape of an inverted U, covered by a glass globe. It had a thumb screw for a switch, the whole device being mounted on a bracket which was used for the return wire. E. C. Shepard, another Englishman, obtained a patent two years later on an incandescent lamp consisting of a weighted hollow charcoal cylinder the end of which pressed against a charcoal cone. Current passing through this high resistance contact, heated the charcoal to incandescence. It operated in a glass globe from which the air could be exhausted. M. J. Roberts obtained an English patent in 1852 on an incandescent lamp. This had a graphite rod for a burner, which could be renewed, mounted in a glass globe. The globe was cemented to a metallic cap fastened to a piece of pipe through which the air could be exhausted. After being exhausted, the pipe, having a stop cock, could be screwed on a stand to support the lamp.

Moses G. Farmer, a professor at the Naval Training Station at Newport, Rhode Island, lighted the parlor of his home at 11 Pearl Street, Salem, Mass., during July, 1859, with several incandescent lamps having a strip of platinum for the burner. The novel feature of this lamp was that the platinum strip was narrower at the terminals than in the center. Heat is conducted away from the terminals and by making the burner thin at these points, the greater resistance of the ends of the burner absorbed more electrical energy thus offsetting the heat being conducted away. This made a more uniform degree of incandescence throughout the length of the burner, and Prof. Farmer obtained a patent on this principle many years later (1882).

Farmer’s Incandescent Lamp, 1859.

This experimental platinum lamp was made by Professor Farmer and several of them lighted the parlor of his home in Salem, Mass.

FURTHER ARC LAMP DEVELOPMENTS

During the ten years, 1850 to 1860, several inventors developed arc lamp mechanisms. Among them was M. J. Roberts, who had invented the graphite incandescent lamp. In Roberts’ arc lamp, which he patented in 1852, the lower carbon was stationary. The upper carbon fitted snugly into an iron tube. In the tube was a brass covered iron rod, which by its weight could push the upper carbon down the tube so the two carbons normally were in contact. An electro-magnet in series with the arc was so located that, when energized, it pulled up the iron tube. This magnet also held the brass covered iron rod from pushing the upper carbon down the tube so that the two carbons were pulled apart, striking the arc. When the arc went out, the iron tube dropped back into its original position, the brass covered iron rod was released, pushing the upper carbon down the tube until the two carbons again touched. This closed the circuit again, striking the arc as before.

Roberts’ Arc Lamp, 1852.

The arc was controlled by an electro-magnet which held an iron tube to which the upper carbon was fastened.

Slater and Watson’s Arc Lamp, 1852.

Clutches were used for the first time in this arc lamp to feed the carbons.

In the same year (1852) Slater and Watson obtained an English patent on an arc lamp in which the upper carbon was movable and held in place by two clutches actuated by electro-magnets. The lower carbon was fixed, and normally the two carbons touched each other. When current was turned on, the electro-magnet lifted the clutches which gripped the upper carbon, pulling it up and striking the arc. This was the first time that a clutch was used to allow the carbon to feed as it became consumed.

Henry Chapman, in 1855, made an arc in which the upper carbon was allowed to feed by gravity, but held in place by a chain wound around a wheel. On this wheel was a brake actuated by an electro-magnet. The lower carbon was pulled down by an electro-magnet working against a spring. When no current was flowing or when the arc went out, the two carbons touched. With current on, one electro-magnet set the brake and held the upper carbon stationary. The other electro-magnet pulled the lower carbon down, thus striking the arc.

None of these mechanisms regulated the length of the arc. It was not until 1856 that Joseph Lacassagne and Henry Thiers, Frenchmen, invented the so-called “differential” method of control, which made the carbons feed when the arc voltage, and hence length, became too great. This principle was used in commercial arc lamps several years afterward when they were operated on series circuits, as it had the added advantage of preventing the feeding of one arc lamp affecting another on the same circuit. This differential control consists in principle of two electro-magnets, one in series with, and opposing the pull of the other which is in shunt with the arc. The series magnet pulls the carbons apart and strikes the arc. As the arc increases in length, its voltage rises, thereby increasing the current flowing through the shunt magnet. This increases the strength of the shunt magnet and, when the arc becomes too long, the strength of the shunt becomes greater than that of the series magnet, thus making the carbons feed.

Diagram of “Differential” Method of Control of an Arc Lamp.

This principle, invented by Lacassagne and Thiers, was used in all arc lamps when they were commercially introduced on a large scale more than twenty years later.

The actual method adopted by Lacassagne and Thiers was different from this, but it had this principle. They used a column of mercury on which the lower carbon floated. The upper carbon was stationary. The height of the mercury column was regulated by a valve connected with a reservoir of mercury. The pull of the series magnet closed the valve fixing the height of the column. The pull of the shunt magnet tended to open the valve, and when it overcame the pull of the series magnet it allowed mercury to flow from the reservoir, raising the height of the column bringing the carbons nearer together. This reduced the arc voltage and shunt magnet strength until the valve closed again. Thus the carbons were always kept the proper distance apart. In first starting the arc, or if the arc should go out, current would only flow through the shunt magnet, bringing the two carbons together until they touched. Current would then flow through the contact of the two carbons and through the series magnet, shutting the valve. There were no means of pulling the carbons apart to strike the arc. Current flowing through the high resistance of the poor contact of the two carbons, heated their tips to incandescence. The incandescent tips would begin to burn away, thus after a time starting an arc. The arc, however, once started was maintained the proper length.

Lacassagne and Thiers’ Differentially Controlled Arc Lamp, 1856.

The lower carbon floated on a column of mercury whose height was “differentially” controlled by series and shunt magnets.

In 1857, Serrin took out his first patent on an arc lamp, the general principles of which were the same as in others he made. The mechanism consisted of two drums, one double the diameter of the other. Both carbons were movable, the upper one feeding down, and the lower one feeding up, being connected with chains wound around the drums. The difference in consumption of the two carbons was therefore compensated for by the difference in size of the drums, thus maintaining the location of the arc in a fixed position. A train of wheels controlled by a pawl and regulated by an electro-magnet, controlled the movement of the carbons. The weight of the upper carbon and its holder actuates the train of wheels.

Serrin’s Arc Lamp, 1857.

This type of arc was not differentially controlled but was the first commercial lamp later used. Both carbons were movable, held by chains wound around drums which were controlled by ratchets actuated by an electro-magnet.

DEVELOPMENT OF THE DYNAMO, 1840–1860

During the first few years after 1840 the dynamo was only a laboratory experiment. Woolrich devised a machine which had several pairs of magnets and double the number of coils in order to make the current obtained less pulsating. Wheatstone in 1845 patented the use of electro-magnets in place of permanent magnets. Brett in 1848 suggested that the current, generated in the coils, be allowed to flow through a coil surrounding each permanent magnet to further strengthen the magnets. Pulvermacher in 1849 proposed the use of thin plates of iron for the bobbins, to reduce the eddy currents generated in the iron. Sinsteden in 1851 suggested that the current from a permanent magnet machine be used to excite the field coils of an electro-magnet machine.

In 1855 Soren Hjorth, of Copenhagen, Denmark, patented a dynamo having both permanent and electro-magnets, the latter being excited by currents first induced in the bobbins by the permanent magnets. In 1856 Dr. Werner Siemens invented the shuttle wound armature. This consisted of a single coil of wire wound lengthwise and counter sunk in a long cylindrical piece of iron. This revolved between the magnet poles which were shaped to fit the cylindrical armature.

Siemens’ Dynamo, 1856.

This dynamo was an improvement over others on account of the construction of its “shuttle” armature.

THE FIRST COMMERCIAL INSTALLATION OF AN ELECTRIC LIGHT

In 1862 a Serrin type of arc lamp was installed in the Dungeness lighthouse in England. Current was supplied by a dynamo made by the Alliance Company, which had been originally designed in 1850 by Nollet, a professor of Physics in the Military School in Brussels. Nollet’s original design was of a dynamo having several rows of permanent magnets mounted radially on a stationary frame, with an equal number of bobbins mounted on a shaft which rotated and had a commutator so direct current could be obtained. A company was formed to sell hydrogen gas for illuminating purposes, the gas to be made by the decomposition of water with current from this machine. Nollet died and the company failed, but it was reorganized as the Alliance Company a few years later to exploit the arc lamp.

Alliance Dynamo, 1862.

This was the dynamo used in the first commercial installation of an arc light in the Dungeness Lighthouse, England, 1862.

About the only change made in the dynamo was to substitute collector rings for the commutator to overcome the difficulties of commutation. Alternating current was therefore generated in this first commercial machine. It had a capacity for but one arc light, which probably consumed less than ten amperes at about 45 volts, hence delivered in the present terminology not over 450 watts or about two-thirds of a horsepower. As the bobbins of the armature undoubtedly had a considerable resistance, the machine had an efficiency of not over 50 per cent and therefore required at least one and a quarter horsepower to drive it.

FURTHER DYNAMO DEVELOPMENTS

In the summer of 1886 Sir Charles Wheatstone constructed a self-excited machine on the principle of using the residual magnetism in the field poles to set up a feeble current in the armature which, passing through the field coils, gradually strengthened the fields until they built up to normal strength. It was later found that this idea had been thought of by an unknown man, being disclosed by a clause in a provisional 1858 English patent taken out by his agent. Wheatstone’s machine was shown to the Royal Society in London and a paper on it read before the Society on February 14, 1867. The field coils were shunt wound.

Wheatstone’s Self-Excited Dynamo, 1866.

This machine was the first self-excited dynamo by use of the residual magnetism in the field poles.

Dr. Werner Siemens also made a self-excited machine, having series fields, a paper on which was read before the Academy of Sciences in Berlin on January 17, 1867. This paper was forwarded to the Royal Society in London and presented at the same meeting at which Wheatstone’s dynamo was described. Wheatstone probably preceded Siemens in this re-discovery of the principle of self-excitation, but both are given the merit of it. However, S. A. Varley on December 24, 1866, obtained a provisional English patent on this, which was not published until July, 1867.

Gramme’s Dynamo, 1871.

These were commercially used, their main feature being the “ring” wound armature.

Gramme’s “Ring” Armature.

Wire coils, surrounding an iron wire core, were all connected together in an endless ring, each coil being tapped with a wire connected to a commutator bar.

In 1870 Gramme, a Frenchman, patented his well-known ring armature. The idea had been previously thought of by Elias, a Hollander, in 1842, and by Pacinnotti, an Italian, as shown by the crude motors (not dynamos) they had made. Gramme’s armature consisted of an iron wire core coated with a bituminous compound in order to reduce the eddy currents. This core was wound with insulated wire coils, all connected together in series as one single endless coil. Each coil was tapped with a wire connected to a commutator bar. His first machine, having permanent magnets for fields, was submitted to the French Academy of Sciences in 1871. Later machines were made with self-excited field coils, which were used in commercial service. They had, however a high resistance armature, so that their efficiency did not exceed 50 per cent.

Alteneck’s Dynamo with “Drum” Wound Armature, 1872.

The armature winding was entirely on the surface of the armature core, a principle now used in all dynamos.

Von Hefner Alteneck, an engineer with Siemens, invented the drum wound armature in 1872. The wires of the armature were all on the surface of the armature core, the wires being tapped at frequent points for connection with the commutator bars. Thus in the early seventies, commercial dynamos were available for use in arc lighting, and a few installations were made in Europe.

RUSSIAN INCANDESCENT LAMP INVENTORS

In 1872 Lodyguine, a Russian scientist, made an incandescent lamp consisting of a “V” shaped piece of graphite for a burner, which operated in nitrogen gas. He lighted the Admiralty Dockyard at St. Petersburg with about two hundred of these lamps. In 1872 the Russian Academy of Sciences awarded him a prize of 50,000 rubles (a lot of real money at that time) for his invention. A company with a capital of 200,000 rubles (then equal to about $100,000) was formed but as the lamp was so expensive to operate and had such a short life, about twelve hours, the project failed.

Lodyguine’s Incandescent Lamp, 1872.

The burner was made of graphite and operated in nitrogen gas.

Konn’s Incandescent Lamp, 1875.

In this lamp the graphite rods operated in a vacuum.

Kosloff, another Russian, in 1875 patented a graphite in nitrogen incandescent lamp, which had several graphite rods for burners, so arranged that when one failed another was automatically connected. Konn, also a Russian, made a lamp similar to Kosloff’s except that the graphite rods operated in a vacuum. Bouliguine, another Russian, in 1876 made an incandescent lamp having a long graphite rod, only the upper part of which was in circuit. As this part burned out, the rod was automatically pushed up so that a fresh portion then was in circuit. It operated in a vacuum. None of these lamps was commercial as they blackened rapidly and were too expensive to maintain.

Bouliguine’s Incandescent Lamp, 1876.

A long graphite rod, the upper part of which only was in circuit, operated in vacuum. As this part burned out, the rod was automatically shoved up, a fresh portion then being in the circuit.

THE JABLOCHKOFF “CANDLE”

Paul Jablochkoff was a Russian army officer and an engineer. In the early seventies he came to Paris and developed a novel arc light. This consisted of a pair of carbons held together side by side and insulated from each other by a mineral known as kaolin which vaporized as the carbons were consumed. There was no mechanism, the arc being started by a thin piece of carbon across the tips of the carbons. Current burned this bridge, starting the arc. The early carbons were about five inches long, and the positive carbon was twice as thick as the negative to compensate for the unequal consumption on direct current. This, however, did not work satisfactorily. Later the length of the carbons was increased, the carbon made of equal thickness and burned on alternating current of about eight or nine amperes at about 45 volts. He made an alternating current generator which had a stationary exterior armature with interior revolving field poles. Several “candles,” as they were called, were put in one fixture to permit all night service and an automatic device was developed, located in each fixture, so that should one “candle” go out for any reason, another was switched into service.

Jablochkoff “Candle,” 1876.

This simple arc consisted of a pair of carbons held together side by side and insulated from each other by kaolin. Several boulevards in Paris were lighted with these arc lights. This arc lamp is in the collection of the Smithsonian Institution.

In 1876 many of these “candles” were installed and later several of the boulevards in Paris were lighted with them. This was the first large installation of the arc light, and was the beginning of its commercial introduction. Henry Wilde made some improvements in the candle by eliminating the kaolin between the carbons which gave Jablochkoff’s arc its peculiar color. Wilde’s arc was started by allowing the ends of the carbons to touch each other, a magnet swinging them apart thus striking the arc.

Jablochkoff’s Alternating Current Dynamo, 1876.

This dynamo had a stationary exterior armature and internal revolving field poles. Alternating current was used for the Jablochkoff “candle” to overcome the difficulties of unequal consumption of the carbons on direct current.

COMMERCIAL INTRODUCTION OF THE DIFFERENTIALLY CONTROLLED ARC LAMP

About the same time Lontin, a Frenchman, improved Serrin’s arc lamp mechanism by the application of series and shunt magnets. This is the differential principle which was invented by Lacassagne and Thiers in 1855 but which apparently had been forgotten. Several of these lamps were commercially installed in France beginning with 1876.

ARC LIGHTING IN THE UNITED STATES

Wallace-Farmer Arc Lamp, 1875.

This “differentially controlled” arc lamp consisted of two slabs of carbon between which the arc played. In the original lamp the carbon slabs were mounted on pieces of wood held in place by bolts, adjustment being made by hitting the upper carbon slab with a hammer. This lamp is in the collection of the Smithsonian Institution.

Wallace-Farmer Dynamo, 1875.

This was the first commercial dynamo used in the United States for arc lighting. This dynamo is in the collection of the Smithsonian Institution.

About 1875 William Wallace of Ansonia, Connecticut, made an arc light consisting of two rectangular carbon plates mounted on a wooden frame. The arc played between the two edges of the plates, which lasted much longer than rods. When the edges had burned away so that the arc then became unduly long, the carbon plates were brought closer together by hitting them with a hammer. Wallace became associated with Moses G. Farmer, and they improved this crude arc by fastening the upper carbon plate to a rod which was held by a clutch controlled by a magnet. This magnet had two coils in one, the inner winding in series with the arc, and outer one in shunt and opposing the series winding. The arc was therefore differentially controlled.

Weston’s Arc Lamp, 1876.

This lamp is in the collection of the Smithsonian Institution.

They also developed a series wound direct current dynamo. The armature consisted of a number of bobbins, all connected together in an endless ring. Each bobbin was also connected to a commutator bar. There were two sets of bobbins, commutators and field poles, the equivalent of two machines in one, which could be connected either to separate circuits, or together in series on one circuit. The Wallace-Farmer system was commercially used. The arc consumed about 20 amperes at about 35 volts, but as the carbon plates cooled the arc, the efficiency was poor. The arc flickered back and forth on the edges of the carbons casting dancing shadows. The carbons, while lasting about 50 hours, were not uniform in density, so the arc would flare up and cast off soot and sparks.

Edward Weston of Newark, New Jersey, also developed an arc lighting system. His commercial lamp had carbon rods, one above the other, and the arc was also differentially controlled. An oil dash pot prevented undue pumping of the carbons. His dynamo had a drum-wound armature, and had several horizontal field coils on each side of one pair of poles between which the armature revolved. The system was designed for about 20 amperes, each are taking about 35 volts.

Brush’s Dynamo, 1877.

This dynamo was used for many years for commercial arc lighting.

Diagram of Brush Armature.

The armature was not a closed circuit. For description of its operation, see text.

Charles F. Brush made a very successful arc lighting system in 1878. His dynamo was unique in that the armature had eight coils, one end of each pair of opposite coils being connected together and the other ends connected to a commutator segment. Thus the armature itself was not a closed circuit. The machine had two pairs of horizontal poles between which the coils revolved. One end of the one pair of coils in the most active position was connected, by means of two of the four brushes, in series with one end of the two pairs of coils in the lesser active position. The latter two pairs of coils were connected in multiple with each other by means of the brushes touching adjacent commutator segments. The outside circuit was connected to the other two brushes, one of which was connected to the other end of the most active pair of coils. The other brush was connected to the other end of the two lesser active pairs of coils. The one pair of coils in the least active position was out of circuit. The field coils were connected in series with the outside circuit.

Brush’s Arc Lamp, 1877.

The carbons were differentially controlled. This lamp was used for many years. This lamp is in the collection of the Smithsonian Institution.

Brush’s arc lamp was also differentially controlled. It was designed for about 10 amperes at about 45 volts. The carbons were copper plated to increase their conductivity. Two pairs of carbons were used for all-night service, each pair lasting about eight hours. A very simple device was used to automatically switch the arc from one to the other pair of carbons, when the first pair was consumed. This device consisted of a triangular-shaped piece of iron connected to the solenoid controlling the arc. There was a groove on each of the outer two corners of this triangle, one groove wider than the other. An iron washer surrounded each upper carbon. The edge of each washer rested in a groove. The washer in the narrow groove made a comparatively tight fit about its carbon. The other washer in the wider groove had a loose fit about its carbon. Pins prevented the washer from falling below given points. Both pairs of carbons touched each other at the start. When current was turned on, the solenoid lifted the triangle, the loose-fitting washer gripped its carbon first, so that current then only passed through the other pair of carbons which were still touching each other. The further movement of the solenoid then separated these carbons, the arc starting between them. When this pair of carbons became consumed, they could not feed any more so that the solenoid would then allow the other pair of carbons to touch, transferring the arc to that pair.

Thomson-Houston Arc Dynamo, 1878.

This dynamo was standard for many years. This machine is in the collection of the Smithsonian Institution.

Elihu Thomson and Edwin J. Houston in 1878 made a very successful and complete arc light system. Their dynamo was specially designed to fit the requirements of the series arc lamp. The Thomson-Houston machine was a bipolar, having an armature consisting of three coils, one end of each of the three coils having a common terminal, or “Y” connected, as it is called. The other end of each coil was connected to a commutator segment. The machine was to a great extent self-regulating, that is the current was inherently constant with fluctuating load, as occurs when the lamps feed or when the number of lamps burning at one time should change for any reason. This regulation was accomplished by what is called “armature reaction,” which is the effect the magnetization of the armature has on the field strength. Close regulation was obtained by a separate electro-magnet, in series with the circuit, which shifted the brushes as the load changed. As there were but three commutator segments, one for each coil, excessive sparking was prevented by an air blast.

Diagram of T-H Arc Lighting System.

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

Thomson-Houston Arc Lamp, 1878.

This is an early model with a single pair of carbons.

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.

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.

Sawyer’s Incandescent Lamp, 1878.

This had a graphite burner operating in nitrogen gas.

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.