He was also naturally in a position to a.s.sume the task he set out to accomplish, of undertaking to plan and-build an improved type of machine that should be commercial in having an efficiency of at least 90 per cent. Truly a prodigious undertaking in those dark days, when from the standpoint of Edison"s large experience the most practical and correct electrical treatise was contained in the Encyclopaedia Britannica, and in a German publication which Mr. Upton had brought with him after he had finished his studies with the ill.u.s.trious Helmholtz. It was at this period that Mr. Upton commenced his a.s.sociation with Edison, bringing to the great work the very latest scientific views and the a.s.sistance of the higher mathematics, to which he had devoted his attention for several years previously.
As some account of Edison"s investigations in this connection has already been given in Chapter XII of the narrative, we shall not enlarge upon them here, but quote from An Historical Review, by Charles L.
Clarke, Laboratory a.s.sistant at Menlo Park, 1880-81; Chief Engineer of the Edison Electric Light Company, 1881-84:
"In June, 1879, was published the account of the Edison dynamo-electric machine that survived in the art. This machine went into extensive commercial use, and was notable for its very ma.s.sive and powerful field-magnets and armature of extremely low resistance as compared with the combined external resistance of the supply-mains and lamps. By means of the large ma.s.ses of iron in the field-magnets, and closely fitted joints between the several parts thereof, the magnetic resistance (reluctance) of the iron parts of the magnetic circuit was reduced to a minimum, and the required magnetization effected with the maximum economy. At the same time Mr. Edison announced the commercial necessity of having the armature of the dynamo of low resistance, as compared with the external resistance, in order that a large percentage of the electrical energy developed should be utilized in the lamps, and only a small percentage lost in the armature, albeit this procedure reduced the total generating capacity of the machine. He also proposed to make the resistance of the supply-mains small, as compared with the combined resistance of the lamps in multiple arc, in order to still further increase the percentage of energy utilized in the lamps. And likewise to this end the combined resistance of the generator armatures in multiple arc was kept relatively small by adjusting the number of generators operating in multiple at any time to the number of lamps then in use.
The field-magnet circuits of the dynamos were connected in multiple with a separate energizing source; and the field-current; and strength of field, were regulated to maintain the required amount of electromotive force upon the supply-mains under all conditions of load from the maximum to the minimum number of lamps in use, and to keep the electromotive force of all machines alike."
Among the earliest of Edison"s dynamo experiments were those relating to the core of the armature. He realized at once that the heat generated in a solid core was a prolific source of loss. He experimented with bundles of iron wires variously insulated, also with sheet-iron rolled cylindrically and covered with iron wire wound concentrically. These experiments and many others were tried in a great variety of ways, until, as the result of all this work, Edison arrived at the principle which has remained in the art to this day. He split up the iron core of the armature into thin laminations, separated by paper, thus practically suppressing Foucault currents therein and resulting heating effect.
It was in his machine also that mica was used for the first time as an insulating medium in a commutator. [27]
[Footnote 27: The commercial manufacture of built-up sheets of mica for electrical purposes was first established at the Edison Machine Works, Goerck Street, New York, in 1881.]
Elementary as these principles will appear to the modern student or engineer, they were denounced as nothing short of absurdity at the time of their promulgation--especially so with regard to Edison"s proposal to upset the then settled dictum that the armature resistance should be equal to the external resistance. His proposition was derided in the technical press of the period, both at home and abroad. As public opinion can be best ill.u.s.trated by actual quotation, we shall present a characteristic instance.
In the Scientific American of October 18, 1879, there appeared an ill.u.s.trated article by Mr. Upton on Edison"s dynamo machine, in which Edison"s views and claims were set forth. A subsequent issue contained a somewhat acrimonious letter of criticism by a well-known maker of dynamo machines. At the risk of being lengthy, we must quote nearly all this letter: "I can scarcely conceive it as possible that the article on the above subject "(Edison"s Electric Generator)" in last week"s Scientific American could have been written from statements derived from Mr. Edison himself, inasmuch as so many of the advantages claimed for the machine described and statements of the results obtained are so manifestly absurd as to indicate on the part of both writer and prompter a positive want of knowledge of the electric circuit and the principles governing the construction and operation of electric machines.
"It is not my intention to criticise the design or construction of the machine (not because they are not open to criticism), as I am now and have been for many years engaged in the manufacture of electric machines, but rather to call attention to the impossibility of obtaining the described results without destroying the doctrine of the conservation and correlation of forces.
"It is stated that "the internal resistance of the armature" of this machine "is only 1/2 ohm." On this fact and the disproportion between this resistance and that of the external circuit, the theory of the alleged efficiency of the machine is stated to be based, for we are informed that, "while this generator in general principle is the same as in the best well-known forms, still there is an all-important difference, which is that it will convert and deliver for useful work nearly double the number of foot-pounds that any other machine will under like conditions."" The writer of this critical letter then proceeds to quote Mr. Upton"s statement of this efficiency: ""Now the energy converted is distributed over the whole resistance, hence if the resistance of the machine be represented by 1 and the exterior circuit by 9, then of the total energy converted nine-tenths will be useful, as it is outside of the machine, and one-tenth is lost in the resistance of the machine.""
After this the critic goes on to say:
"How any one acquainted with the laws of the electric circuit can make such statements is what I cannot understand. The statement last quoted is mathematically absurd. It implies either that the machine is CAPABLE OF INCREASING ITS OWN ELECTROMOTIVE FORCE NINE TIMES WITHOUT AN INCREASED EXPENDITURE OF POWER, or that external resistance is NOT resistance to the current induced in the Edison machine.
"Does Mr. Edison, or any one for him, mean to say that r/n enables him to obtain nE, and that C IS NOT = E / (r/n + R)? If so Mr. Edison has discovered something MORE than perpetual motion, and Mr. Keely had better retire from the field.
"Further on the writer (Mr. Upton) gives us another example of this mode of reasoning when, emboldened and satisfied with the absurd theory above exposed, he endeavors to prove the cause of the inefficiency of the Siemens and other machines. Couldn"t the writer of the article see that since C = E/(r + R) that by R/n or by making R = r, the machine would, according to his theory, have returned more useful current to the circuit than could be due to the power employed (and in the ratio indicated), so that there would actually be a creation of force! . . . .
"In conclusion allow me to say that if Mr Edison thinks he has accomplished so much by the REDUCTION OF THE INTERNAL RESISTANCE of his machine, that he has much more to do in this direction before his machine will equal IN THIS RESPECT others already in the market."
Another partic.i.p.ant in the controversy on Edison"s generator was a scientific gentleman, who in a long article published in the Scientific American, in November, 1879, gravely undertook to instruct Edison in the A B C of electrical principles, and then proceeded to demonstrate mathematically the IMPOSSIBILITY of doing WHAT EDISON HAD ACTUALLY DONE.
This critic concludes with a gentle rebuke to the inventor for ill-timed jesting, and a suggestion to furnish AUTHENTIC information!
In the light of facts, as they were and are, this article is so full of humor that we shall indulge in a few quotations It commences in A B C fashion as follows: "Electric machines convert mechanical into electrical energy.... The ratio of yield to consumption is the expression of the efficiency of the machine.... How many foot-pounds of electricity can be got out of 100 foot-pounds of mechanical energy?
Certainly not more than 100: certainly less.... The facts and laws of physics, with the a.s.sistance of mathematical logic, never fail to furnish precious answers to such questions."
The would-be critic then goes on to tabulate tests of certain other dynamo machines by a committee of the Franklin Inst.i.tute in 1879, the results of which showed that these machines returned about 50 per cent.
of the applied mechanical energy, ingenuously remarking: "Why is it that when we have produced the electricity, half of it must slip away? Some persons will be content if they are told simply that it is a way which electricity has of behaving. But there is a satisfactory rational explanation which I believe can be made plain to persons of ordinary intelligence. It ought to be known to all those who are making or using machines. I am grieved to observe that many persons who talk and write glibly about electricity do not understand it; some even ignore or deny the fact to be explained."
Here follows HIS explanation, after which he goes on to say: "At this point plausibly comes in a suggestion that the internal part of the circuit be made very small and the external part very large. Why not (say) make the internal part 1 and the external 9, thus saving nine-tenths and losing only one-tenth? Unfortunately, the suggestion is not practical; a fallacy is concealed in it."
He then goes on to prove his case mathematically, to his own satisfaction, following it sadly by condoling with and a warning to Edison: "But about Edison"s electric generator! . . . No one capable of making the improvements in the telegraph and telephone, for which we are indebted to Mr. Edison, could be other than an accomplished electrician.
His reputation as a scientist, indeed, is smirched by the newspaper exaggerations, and no doubt he will be more careful in future. But there is a danger nearer home, indeed, among his own friends and in his very household.
". . . The writer of page 242" (the original article) "is probably a friend of Mr. Edison, but possibly, alas! a wicked partner. Why does he say such things as these? "Mr. Edison claims that he realizes 90 per cent. of the power applied to this machine in external work." . . .
Perhaps the writer is a humorist, and had in his mind Colonel Sellers, etc., which he could not keep out of a serious discussion; but such jests are not good.
"Mr. Edison has built a very interesting machine, and he has the opportunity of making a valuable contribution to the electrical arts by furnishing authentic accounts of its capabilities."
The foregoing extracts are unavoidably lengthy, but, viewed in the light of facts, serve to ill.u.s.trate most clearly that Edison"s conceptions and work were far and away ahead of the comprehension of his contemporaries in the art, and that his achievements in the line of efficient dynamo design and construction were indeed truly fundamental and revolutionary in character. Much more of similar nature to the above could be quoted from other articles published elsewhere, but the foregoing will serve as instances generally representing all. In the controversy which appeared in the columns of the Scientific American, Mr. Upton, Edison"s mathematician, took up the question on his side, and answered the critics by further elucidations of the principles on which Edison had founded such remarkable and radical improvements in the art. The type of Edison"s first dynamo-electric machine, the description of which gave rise to the above controversy, is shown in Fig. 1.
Any account of Edison"s work on the dynamo would be incomplete did it omit to relate his conception and construction of the great direct-connected steam-driven generator that was the prototype of the colossal units which are used throughout the world to-day.
In the demonstrating plant installed and operated by him at Menlo Park in 1880 ten dynamos of eight horse-power each were driven by a slow-speed engine through a complicated system of counter-shafting, and, to quote from Mr. Clarke"s Historical Review, "it was found that a considerable percentage of the power of the engine was necessarily wasted in friction by this method of driving, and to prevent this waste and thus increase the economy of his system, Mr. Edison conceived the idea of subst.i.tuting a single large dynamo for the several small dynamos, and directly coupling it with the driving engine, and at the same time preserve the requisite high armature speed by using an engine of the high-speed type. He also expected to realize still further gains in economy from the use of a large dynamo in place of several small machines by a more than correspondingly lower armature resistance, less energy for magnetizing the field, and for other minor reasons. To the same end, he intended to supply steam to the engine under a much higher boiler pressure than was customary in stationary-engine driving at that time."
The construction of the first one of these large machines was commenced late in the year 1880. Early in 1881 it was completed and tested, but some radical defects in armature construction were developed, and it was also demonstrated that a rate of engine speed too high for continuously safe and economical operation had been chosen. The machine was laid aside. An accurate ill.u.s.tration of this machine, as it stood in the engine-room at Menlo Park, is given in Van Nostrand"s Engineering Magazine, Vol. XXV, opposite page 439, and a brief description is given on page 450.
With the experience thus gained, Edison began, in the spring of 1881, at the Edison Machine Works, Goerck Street, New York City, the construction of the first successful machine of this type. This was the great machine known as "Jumbo No. 1," which is referred to in the narrative as having been exhibited at the Paris International Electrical Exposition, where it was regarded as the wonder of the electrical world. An intimation of some of the tremendous difficulties encountered in the construction of this machine has already been given in preceding pages, hence we shall not now enlarge on the subject, except to note in pa.s.sing that the terribly destructive effects of the spark of self-induction and the arcing following it were first manifested in this powerful machine, but were finally overcome by Edison after a strenuous application of his powers to the solution of the problem.
It may be of interest, however, to mention some of its dimensions and electrical characteristics, quoting again from Mr. Clarke: "The field-magnet had eight solid cylindrical cores, 8 inches in diameter and 57 inches long, upon each of which was wound an exciting-coil of 3.2 ohms resistance, consisting of 2184 turns of No. 10 B. W. G. insulated copper wire, disposed in six layers. The laminated iron core of the armature, formed of thin iron disks, was 33 3/4 inches long, and had an internal diameter of 12 1/2 inches, and an external diameter of 26 7/16 inches. It was mounted on a 6-inch shaft. The field-poles were 33 3/4 inches long, and 27 1/2 inches inside diameter The armature winding consisted of 146 copper bars on the face of the core, connected into a closed-coil winding by means of 73 copper disks at each end of the core.
The cross-sectional area of each bar was 0.2 square inch their average length was 42.7 inches, and the copper end-disks were 0.065 inch thick.
The commutator had 73 sections. The armature resistance was 0.0092 ohm, [28] of which 0.0055 ohm was in the armature bars and 0.0037 ohm in the end-disks." An ill.u.s.tration of the next latest type of this machine is presented in Fig. 2.
[Footnote 28: Had Edison in Upton"s Scientific American article in 1879 proposed such an exceedingly low armature resistance for this immense generator (although its ratio was proportionate to the original machine), his critics might probably have been sufficiently indignant as to be unable to express themselves coherently.]
The student may find it interesting to look up Edison"s United States Patents Nos. 242,898, 263,133, 263,146, and 246,647, bearing upon the construction of the "Jumbo"; also ill.u.s.trated articles in the technical journals of the time, among which may be mentioned: Scientific American, Vol. XLV, page 367; Engineering, London, Vol. x.x.xII, pages 409 and 419, The Telegraphic Journal and Electrical Review, London, Vol. IX, pages 431-433, 436-446; La Nature, Paris, 9th year, Part II, pages 408-409; Zeitschrift fur Angewandte Elektricitaatslehre, Munich and Leipsic, Vol.
IV, pages 4-14; and Dredge"s Electric Illumination, 1882, Vol. I, page 261.
The further development of these great machines later on, and their extensive practical use, are well known and need no further comment, except in pa.s.sing it may be noted that subsequent machines had each a capacity of 1200 lamps of 16 candle-power, and that the armature resistance was still further reduced to 0.0039 ohm.
Edison"s clear insight into the future, as ill.u.s.trated by his persistent advocacy of large direct-connected generating units, is abundantly vindicated by present-day practice. His Jumbo machines, of 175 horse-power, so enormous for their time, have served as prototypes, and have been succeeded by generators which have constantly grown in size and capacity until at this time (1910) it is not uncommon to employ such generating units of a capacity of 14,000 kilowatts, or about 18,666 horse-power.
We have not entered into specific descriptions of the many other forms of dynamo machines invented by Edison, such as the multipolar, the disk dynamo, and the armature with two windings, for sub-station distribution; indeed, it is not possible within our limited s.p.a.ce to present even a brief digest of Edison"s great and comprehensive work on the dynamo-electric machine, as embodied in his extensive experiments and in over one hundred patents granted to him. We have, therefore, confined ourselves to the indication of a few salient and basic features, leaving it to the interested student to examine the patents and the technical literature of the long period of time over which Edison"s labors were extended.
Although he has not given any attention to the subject of generators for many years, an interesting instance of his incisive method of overcoming minor difficulties occurred while the present volumes were under preparation (1909). Carbon for commutator brushes has been superseded by graphite in some cases, the latter material being found much more advantageous, electrically. Trouble developed, however, for the reason that while carbon was hard and would wear away the mica insulation simultaneously with the copper, graphite, being softer, would wear away only the copper, leaving ridges of mica and thus causing sparking through unequal contact. At this point Edison was asked to diagnose the trouble and provide a remedy. He suggested the cutting out of the mica pieces almost to the bottom, leaving the commutator bars separated by air-s.p.a.ces. This scheme was objected to on the ground that particles of graphite would fill these air-s.p.a.ces and cause a short-circuit. His answer was that the air-s.p.a.ces const.i.tuted the value of his plan, as the particles of graphite falling into them would be thrown out by the action of centrifugal force as the commutator revolved. And thus it occurred as a matter of fact, and the trouble was remedied. This idea was subsequently adopted by a great manufacturer of generators.
XI. THE EDISON FEEDER SYSTEM
TO quote from the preamble of the specifications of United States Patent No. 264,642, issued to Thomas A. Edison September 19, 1882: "This invention relates to a method of equalizing the tension or "pressure"
of the current through an entire system of electric lighting or other translation of electric force, preventing what is ordinarily known as a "drop" in those portions of the system the more remote from the central station...."
The problem which was solved by the Edison feeder system was that relating to the equal distribution of current on a large scale over extended areas, in order that a constant and uniform electrical pressure could be maintained in every part of the distribution area without prohibitory expenditure for copper for mains and conductors.
This problem had a twofold aspect, although each side was inseparably bound up in the other. On the one hand it was obviously necessary in a lighting system that each lamp should be of standard candle-power, and capable of interchangeable use on any part of the system, giving the same degree of illumination at every point, whether near to or remote from the source of electrical energy. On the other hand, this must be accomplished by means of a system of conductors so devised and arranged that while they would insure the equal pressure thus demanded, their ma.s.s and consequent cost would not exceed the bounds of practical and commercially economical investment.
The great importance of this invention can be better understood and appreciated by a brief glance at the state of the art in 1878-79, when Edison was conducting the final series of investigations which culminated in his invention of the incandescent lamp and SYSTEM of lighting. At this time, and for some years previously, the scientific world had been working on the "subdivision of the electric light," as it was then termed. Some leading authorities p.r.o.nounced it absolutely impossible of achievement on any extended scale, while a very few others, of more optimistic mind, could see no gleam of light through the darkness, but confidently hoped for future developments by such workers as Edison.
The earlier investigators, including those up to the period above named, thought of the problem as involving the subdivision of a FIXED UNIT of current, which, being sufficient to cause illumination by one large lamp, might be divided into a number of small units whose aggregate light would equal the candle-power of this large lamp. It was found, however, in their experiments that the contrary effect was produced, for with every additional lamp introduced in the circuit the total candle-power decreased instead of increasing. If they were placed in series the light varied inversely as the SQUARE of the number of lamps in circuit; while if they were inserted in multiple arc, the light diminished as the CUBE of the number in circuit. [29] The idea of maintaining a constant potential and of PROPORTIONING THE CURRENT to the number of lamps in circuit did not occur to most of these early investigators as a feasible method of overcoming the supposed difficulty.
[Footnote 29: M. Fontaine, in his book on Electric Lighting (1877), showed that with the current of a battery composed of sixteen elements, one lamp gave an illumination equal to 54 burners; whereas two similar lamps, if introduced in parallel or multiple arc, gave the light of only 6 1/2 burners in all; three lamps of only 2 burners in all; four lamps of only 3/4 of one burner, and five lamps of 1/4 of a burner.]