To reproduce this record it was only necessary to again start at the beginning and cause the needle to retrace its path in the spiral line.

The needle, in pa.s.sing rapidly in contact with the recorded waves, was vibrated up and down, causing corresponding vibrations of the diaphragm.

In this way sound-waves similar to those caused by the original sounds would be set up in the air, thus reproducing the original speech.

The modern phonograph operates in a precisely similar way, the only difference being in details of refinement. Instead of tin-foil, a wax cylinder is employed, the record being cut thereon by a cutting-tool attached to a diaphragm, while the reproduction is effected by means of a blunt stylus similarly attached.

The cutting-tool and stylus are devices made of sapphire, a gem next in hardness to a diamond, and they have to be cut and formed to an exact nicety by means of diamond dust, most of the work being performed under high-powered microscopes. The minute proportions of these devices will be apparent by a glance at the accompanying ill.u.s.trations, in which the object on the left represents a common pin, and the objects on the right the cutting-tool and reproducing stylus, all actual sizes.

In the next ill.u.s.tration (Fig. 4) there is shown in the upper sketch, greatly magnified, the cutting or recording tool in the act of forming the record, being vibrated rapidly by the diaphragm; and in the lower sketch, similarly enlarged, a representation of the stylus travelling over the record thus made, in the act of effecting a reproduction.

From the late summer of 1878 and to the fall of 1887 Edison was intensely busy on the electric light, electric railway, and other problems, and virtually gave no attention to the phonograph. Hence, just prior to the latter-named period the instrument was still in its tin-foil age; but he then began to devote serious attention to the development of an improved type that should be of greater commercial importance. The practical results are too well known to call for further comment. That his efforts were not limited in extent may be inferred from the fact that since the fall of 1887 to the present writing he has been granted in the United States one hundred and four patents relating to the phonograph and its accessories.

Interesting as the numerous inventions are, it would be a work of supererogation to digest all these patents in the present pages, as they represent not only the inception but also the gradual development and growth of the wax-record type of phonograph from its infancy to the present perfected machine and records now so widely known all over the world. From among these many inventions, however, we will select two or three as examples of ingenuity and importance in their bearing upon present perfection of results.

One of the difficulties of reproduction for many years was the trouble experienced in keeping the stylus in perfect engagement with the wave-like record, so that every minute vibration would be reproduced. It should be remembered that the deepest cut of the recording tool is only about one-third the thickness of tissue-paper. Hence, it will be quite apparent that the slightest inequality in the surface of the wax would be sufficient to cause false vibration, and thus give rise to distorted effects in such music or other sounds as were being reproduced. To remedy this, Edison added an attachment which is called a "floating weight," and is shown at A in the ill.u.s.tration above.

The function of the floating weight is to automatically keep the stylus in close engagement with the record, thus insuring accuracy of reproduction. The weight presses the stylus to its work, but because of its ma.s.s it cannot respond to the extremely rapid vibrations of the stylus. They are therefore communicated to the diaphragm.

Some of Edison's most remarkable inventions are revealed in a number of interesting patents relating to the duplication of phonograph records.

It would be obviously impossible, from a commercial standpoint, to obtain a musical record from a high-cla.s.s artist and sell such an original to the public, as its cost might be from one hundred to several thousand dollars. Consequently, it is necessary to provide some way by which duplicates may be made cheaply enough to permit their purchase by the public at a reasonable price.

The making of a perfect original musical or other record is a matter of no small difficulty, as it requires special technical knowledge and skill gathered from many years of actual experience; but in the exact copying, or duplication, of such a record, with its many millions of microscopic waves and sub-waves, the difficulties are enormously increased. The duplicates must be microscopically identical with the original, they must be free from false vibrations or other defects, although both original and duplicates are of such easily defacable material as wax; and the process must be cheap and commercial not a scientific laboratory possibility.

For making duplicates it was obviously necessary to first secure a mold carrying the record in negative or reversed form. From this could be molded, or cast, positive copies which would be identical with the original. While the art of electroplating would naturally suggest itself as the means of making such a mold, an apparently insurmountable obstacle appeared on the very threshold. Wax, being a non-conductor, cannot be electroplated unless a conducting surface be first applied.

The coatings ordinarily used in electro-deposition were entirely out of the question on account of coa.r.s.eness, the deepest waves of the record being less than one-thousandth of an inch in depth, and many of them probably ten to one hundred times as shallow. Edison finally decided to apply a preliminary metallic coating of infinitesimal thinness, and accomplished this object by a remarkable process known as the vacuous deposit. With this he applied to the original record a film of gold probably no thicker than one three-hundred-thousandth of an inch, or several hundred times less than the depth of an average wave. Three hundred such layers placed one on top of the other would make a sheet no thicker than tissue-paper.

The process consists in placing in a vacuum two leaves, or electrodes, of gold, and between them the original record. A constant discharge of electricity of high tension between the electrodes is effected by means of an induction-coil. The metal is vaporized by this discharge, and is carried by it directly toward and deposited upon the original record, thus forming the minute film of gold above mentioned. The record is constantly rotated until its entire surface is coated. A sectional diagram of the apparatus (Fig. 6.) will aid to a clearer understanding of this ingenious process.

After the gold film is formed in the manner described above, a heavy backing of baser metal is electroplated upon it, thus forming a substantial mold, from which the original record is extracted by breakage or shrinkage.

Duplicate records in any quant.i.ty may now be made from this mold by surrounding it with a cold-water jacket and dipping it in a molten wax-like material. This congeals on the record surface just as melted b.u.t.ter would collect on a cold knife, and when the mold is removed the surplus wax falls out, leaving a heavy deposit of the material which forms the duplicate record. Numerous ingenious inventions have been made by Edison providing for a variety of rapid and economical methods of duplication, including methods of shrinking a newly made copy to facilitate its quick removal from the mold; methods of reaming, of forming ribs on the interior, and for many other important and essential details, which limits of s.p.a.ce will not permit of elaboration. Those mentioned above are but fair examples of the persistent and effective work he has done to bring the phonograph to its present state of perfection.

In perusing Chapter X of the foregoing narrative, the reader undoubtedly noted Edison's clear apprehension of the practical uses of the phonograph, as evidenced by his prophetic utterances in the article written by him for the North American Review in June, 1878. In view of the crudity of the instrument at that time, it must be acknowledged that Edison's foresight, as vindicated by later events was most remarkable.

No less remarkable was his intensely practical grasp of mechanical possibilities of future types of the machine, for we find in one of his early English patents (No. 1644 of 1878) the disk form of phonograph which, some ten to fifteen years later, was supposed to be a new development in the art. This disk form was also covered by Edison's application for a United States patent, filed in 1879. This application met with some merely minor technical objections in the Patent Office, and seems to have pa.s.sed into the "abandoned" cla.s.s for want of prosecution, probably because of being overlooked in the tremendous pressure arising from his development of his electric-lighting system.

IX. THE INCANDESCENT LAMP

ALTHOUGH Edison's contributions to human comfort and progress are extensive in number and extraordinarily vast and comprehensive in scope and variety, the universal verdict of the world points to his incandescent lamp and system of distribution of electrical current as the central and crowning achievements of his life up to this time. This view would seem entirely justifiable when we consider the wonderful changes in the conditions of modern life that have been brought about by the wide-spread employment of these inventions, and the gigantic industries that have grown up and been nourished by their world-wide application. That he was in this instance a true pioneer and creator is evident as we consider the subject, for the United States Patent No.

223,898, issued to Edison on January 27, 1880, for an incandescent lamp, was of such fundamental character that it opened up an entirely new and tremendously important art--the art of incandescent electric lighting.

This statement cannot be successfully controverted, for it has been abundantly verified after many years of costly litigation. If further proof were desired, it is only necessary to point to the fact that, after thirty years of most strenuous and practical application in the art by the keenest intellects of the world, every incandescent lamp that has ever since been made, including those of modern days, is still dependent upon the employment of the essentials disclosed in the above-named patent--namely, a filament of high resistance enclosed in a sealed gla.s.s globe exhausted of air, with conducting wires pa.s.sing through the gla.s.s.

An incandescent lamp is such a simple-appearing article--merely a filament sealed into a gla.s.s globe--that its intrinsic relation to the art of electric lighting is far from being apparent at sight. To the lay mind it would seem that this must have been THE obvious device to make in order to obtain electric light by incandescence of carbon or other material. But the reader has already learned from the preceding narrative that prior to its invention by Edison such a device was NOT obvious, even to the most highly trained experts of the world at that period; indeed, it was so far from being obvious that, for some time after he had completed practical lamps and was actually lighting them up twenty-four hours a day, such a device and such a result were declared by these same experts to be an utter impossibility. For a short while the world outside of Menlo Park held Edison's claims in derision.

His lamp was p.r.o.nounced a fake, a myth, possibly a momentary success magnified to the dignity of a permanent device by an overenthusiastic inventor.

Such criticism, however, did not disturb Edison. He KNEW that he had reached the goal. Long ago, by a close process of reasoning, he had clearly seen that the only road to it was through the path he had travelled, and which was now embodied in the philosophy of his incandescent lamp--namely, a filament, or carbon, of high resistance and small radiating surface, sealed into a gla.s.s globe exhausted of air to a high degree of vacuum. In originally committing himself to this line of investigation he was well aware that he was going in a direction diametrically opposite to that followed by previous investigators. Their efforts had been confined to low-resistance burners of large radiating surface for their lamps, but he realized the utter futility of such devices. The tremendous problems of heat and the prohibitive quant.i.ties of copper that would be required for conductors for such lamps would be absolutely out of the question in commercial practice.

He was convinced from the first that the true solution of the problem lay in a lamp which should have as its illuminating body a strip of material which would offer such a resistance to the flow of electric current that it could be raised to a high temperature--incandescence--and be of such small cross-section that it would radiate but little heat. At the same time such a lamp must require a relatively small amount of current, in order that comparatively small conductors could be used, and its burner must be capable of withstanding the necessarily high temperatures without disintegration.

It is interesting to note that these conceptions were in Edison's mind at an early period of his investigations, when the best expert opinion was that the subdivision of the electric current was an ignis fatuus.

Hence we quote the following notes he made, November 15, 1878, in one of the laboratory note-books:

"A given straight wire having 1 ohm resistance and certain length is brought to a given degree of temperature by given battery. If the same wire be coiled in such a manner that but one-quarter of its surface radiates, its temperature will be increased four times with the same battery, or, one-quarter of this battery will bring it to the temperature of straight wire. Or the same given battery will bring a wire whose total resistance is 4 ohms to the same temperature as straight wire.

"This was actually determined by trial.

"The amount of heat lost by a body is in proportion to the radiating surface of that body. If one square inch of platina be heated to 100 degrees it will fall to, say, zero in one second, whereas, if it was at 200 degrees it would require two seconds.

"Hence, in the case of incandescent conductors, if the radiating surface be twelve inches and the temperature on each inch be 100, or 1200 for all, if it is so coiled or arranged that there is but one-quarter, or three inches, of radiating surface, then the temperature on each inch will be 400. If reduced to three-quarters of an inch it will have on that three-quarters of an inch 1600 degrees Fahr., notwithstanding the original total amount was but 1200, because the radiation has been reduced to three-quarters, or 75 units; hence, the effect of the lessening of the radiation is to raise the temperature of each remaining inch not radiating to 125 degrees. If the radiating surface should be reduced to three-thirty-seconds of an inch, the temperature would reach 6400 degrees Fahr. To carry out this law to the best advantage in regard to platina, etc., then with a given length of wire to quadruple the heat we must lessen the radiating surface to one-quarter, and to do this in a spiral, three-quarters must be within the spiral and one-quarter outside for radiating; hence, a square wire or other means, such as a spiral within a spiral, must be used. These results account for the enormous temperature of the Electric Arc with one horse-power; as, for instance, if one horse-power will heat twelve inches of wire to 1000 degrees Fahr., and this is concentrated to have one-quarter of the radiating surface, it would reach a temperature of 4000 degrees or sufficient to melt it; but, supposing it infusible, the further concentration to one-eighth its surface, it would reach a temperature of 16,000 degrees, and to one-thirty-second its surface, which would be about the radiating surface of the Electric Arc, it would reach 64,000 degrees Fahr. Of course, when Light is radiated in great quant.i.ties not quite these temperatures would be reached.

"Another curious law is this: It will require a greater initial battery to bring an iron wire of the same size and resistance to a given temperature than it will a platina wire in proportion to their specific heats, and in the case of Carbon, a piece of Carbon three inches long and one-eighth diameter, with a resistance of 1 ohm, will require a greater battery power to bring it to a given temperature than a cylinder of thin platina foil of the same length, diameter, and resistance, because the specific heat of Carbon is many times greater; besides, if I am not mistaken, the radiation of a roughened body for heat is greater than a polished one like platina."

Proceeding logically upon these lines of thought and following them out through many ramifications, we have seen how he at length made a filament of carbon of high resistance and small radiating surface, and through a concurrent investigation of the phenomena of high vacua and occluded gases was able to produce a true incandescent lamp. Not only was it a lamp as a mere article--a device to give light--but it was also an integral part of his great and complete system of lighting, to every part of which it bore a fixed and definite ratio, and in relation to which it was the keystone that held the structure firmly in place.

The work of Edison on incandescent lamps did not stop at this fundamental invention, but extended through more than eighteen years of a most intense portion of his busy life. During that period he was granted one hundred and forty-nine other patents on the lamp and its manufacture. Although very many of these inventions were of the utmost importance and value, we cannot attempt to offer a detailed exposition of them in this necessarily brief article, but must refer the reader, if interested, to the patents themselves, a full list being given at the end of this Appendix. The outline sketch will indicate the princ.i.p.al patents covering the basic features of the lamp.

The litigation on the Edison lamp patents was one of the most determined and stubbornly fought contests in the history of modern jurisprudence.

Vast interests were at stake. All of the technical, expert, and professional skill and knowledge that money could procure or experience devise were availed of in the bitter fights that raged in the courts for many years. And although the Edison interests had spent from first to last nearly $2,000,000, and had only about three years left in the life of the fundamental patent, Edison was thoroughly sustained as to priority by the decisions in the various suits. We shall offer a few brief extracts from some of these decisions.

In a suit against the United States Electric Lighting Company, United States Circuit Court for the Southern District of New York, July 14, 1891, Judge Wallace said, in his opinion: "The futility of hoping to maintain a burner in vacuo with any permanency had discouraged prior inventors, and Mr. Edison is ent.i.tled to the credit of obviating the mechanical difficulties which disheartened them.... He was the first to make a carbon of materials, and by a process which was especially designed to impart high specific resistance to it; the first to make a carbon in the special form for the special purpose of imparting to it high total resistance; and the first to combine such a burner with the necessary adjuncts of lamp construction to prevent its disintegration and give it sufficiently long life. By doing these things he made a lamp which was practically operative and successful, the embryo of the best lamps now in commercial use, and but for which the subdivision of the electric light by incandescence would still be nothing but the ignis fatuus which it was proclaimed to be in 1879 by some of the reamed experts who are now witnesses to belittle his achievement and show that it did not rise to the dignity of an invention.... It is impossible to resist the conclusion that the invention of the slender thread of carbon as a subst.i.tute for the burners previously employed opened the path to the practical subdivision of the electric light."

An appeal was taken in the above suit to the United States Circuit Court of Appeals, and on October 4, 1892, the decree of the lower court was affirmed. The judges (Lacombe and Shipman), in a long opinion reviewed the facts and the art, and said, inter alia: "Edison's invention was practically made when he ascertained the theretofore unknown fact that carbon would stand high temperature, even when very attenuated, if operated in a high vacuum, without the phenomenon of disintegration.

This fact he utilized by the means which he has described, a lamp having a filamentary carbon burner in a nearly perfect vacuum."

In a suit against the Boston Incandescent Lamp Company et al., in the United States Circuit Court for the District of Ma.s.sachusetts, decided in favor of Edison on June 11, 1894, Judge Colt, in his opinion, said, among other things: "Edison made an important invention; he produced the first practical incandescent electric lamp; the patent is a pioneer in the sense of the patent law; it may be said that his invention created the art of incandescent electric lighting."

Opinions of other courts, similar in tenor to the foregoing, might be cited, but it would be merely in the nature of reiteration. The above are sufficient to ill.u.s.trate the direct clearness of judicial decision on Edison's position as the founder of the art of electric lighting by incandescence.

X. EDISON'S DYNAMO WORK

AT the present writing, when, after the phenomenally rapid electrical development of thirty years, we find on the market a great variety of modern forms of efficient current generators advertised under the names of different inventors (none, however, bearing the name of Edison), a young electrical engineer of the present generation might well inquire whether the great inventor had ever contributed anything to the art beyond a mere TYPE of machine formerly made and bearing his name, but not now marketed except second hand.

For adequate information he might search in vain the books usually regarded as authorities on the subject of dynamo-electric machinery, for with slight exceptions there has been a singular unanimity in the omission of writers to give Edison credit for his great and basic contributions to heavy-current technics, although they have been universally acknowledged by scientific and practical men to have laid the foundation for the efficiency of, and to be embodied in all modern generators of current.

It might naturally be expected that the essential facts of Edison's work would appear on the face of his numerous patents on dynamo-electric machinery, but such is not necessarily the case, unless they are carefully studied in the light of the state of the art as it existed at the time. While some of these patents (especially the earlier ones) cover specific devices embodying fundamental principles that not only survive to the present day, but actually lie at the foundation of the art as it now exists, there is no revelation therein of Edison's preceding studies of magnets, which extended over many years, nor of his later systematic investigations and deductions.

Dynamo-electric machines of a primitive kind had been invented and were in use to a very limited extent for arc lighting and electroplating for some years prior to the summer of 1819, when Edison, with an embryonic lighting SYSTEM in mind, cast about for a type of machine technically and commercially suitable for the successful carrying out of his plans.

He found absolutely none. On the contrary, all of the few types then obtainable were uneconomical, indeed wasteful, in regard to efficiency.

The art, if indeed there can be said to have been an art at that time, was in chaotic confusion, and only because of Edison's many years' study of the magnet was he enabled to conclude that insufficiency in quant.i.ty of iron in the magnets of such machines, together with poor surface contacts, rendered the cost of magnetization abnormally high. The heating of solid armatures, the only kind then known, and poor insulation in the commutators, also gave rise to serious losses. But perhaps the most serious drawback lay in the high-resistance armature, based upon the highest scientific dictum of the time that in order to obtain the maximum amount of work from a machine, the internal resistance of the armature must equal the resistance of the exterior circuit, although the application of this principle entailed the useless expenditure of at least 50 per cent. of the applied energy.

It seems almost incredible that only a little over thirty years ago the sum of scientific knowledge in regard to dynamo-electric machines was so meagre that the experts of the period should settle upon such a dictum as this, but such was the fact, as will presently appear. Mechanical generators of electricity were comparatively new at that time; their theory and practice were very imperfectly understood; indeed, it is quite within the bounds of truth to say that the correct principles were befogged by reason of the lack of practical knowledge of their actual use. Electricians and scientists of the period had been accustomed for many years past to look to the chemical battery as the source from which to obtain electrical energy; and in the practical application of such energy to telegraphy and kindred uses, much thought and ingenuity had been expended in studying combinations of connecting such cells so as to get the best results. In the text-books of the period it was stated as a settled principle that, in order to obtain the maximum work out of a set of batteries, the internal resistance must approximately equal the resistance of the exterior circuit. This principle and its application in practice were quite correct as regards chemical batteries, but not as regards dynamo machines. Both were generators of electrical current, but so different in construction and operation, that rules applicable to the practical use of the one did not apply with proper commercial efficiency to the other. At the period under consideration, which may be said to have been just before dawn of the day of electric light, the philosophy of the dynamo was seen only in mysterious, hazy outlines--just emerging from the darkness of departing night. Perhaps it is not surprising, then, that the dynamo was loosely regarded by electricians as the practical equivalent of a chemical battery; that many of the characteristics of performance of the chemical cell were also attributed to it, and that if the maximum work could be gotten out of a set of batteries when the internal and external resistances were equal (and this was commercially the best thing to do), so must it be also with a dynamo.

It was by no miracle that Edison was far and away ahead of his time when he undertook to improve the dynamo. He was possessed of absolute KNOWLEDGE far beyond that of his contemporaries. This he ad acquired by the hardest kind of work and incessant experiment with magnets of all kinds during several years preceding, particularly in connection with his study of automatic telegraphy. His knowledge of magnets was tremendous. He had studied and experimented with electromagnets in enormous variety, and knew their peculiarities in charge and discharge, lag, self-induction, static effects, condenser effects, and the various other phenomena connected therewith. He had also made collateral studies of iron, steel, and copper, insulation, winding, etc. Hence, by reason of this extensive work and knowledge, Edison was naturally in a position to realize the utter commercial impossibility of the then best dynamo machine in existence, which had an efficiency of only about 40 per cent., and was constructed on the "cut-and-try" principle.