Part 3

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.

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 = C^{2}R 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

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

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).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.