MISCELLANEOUS INVENTIONS

IT has been the endeavor in this narrative to group Edison's inventions and patents so that his work in the different fields can be studied independently and separately. The history of his career has therefore fallen naturally into a series of chapters, each aiming to describe some particular development or art; and, in a way, the plan has been helpful to the writers while probably useful to the readers. It happens, however, that the process has left a vast mass of discovery and invention wholly untouched, and relegates to a concluding brief chapter some of the most interesting episodes of a fruitful life. Any one who will turn to the list of Edison patents at the end of the book will find a large number of things of which not even casual mention has been made, but which at the time occupied no small amount of the inventor's time and attention, and many of which are now part and parcel of modern civilization. Edison has, indeed, touched nothing that he did not in some way improve. As Thoreau said: "The laws of the Universe are not indifferent, but are forever on the side of the most sensitive," and there never was any one more sensitive to the defects of every art and appliance, nor any one more active in applying the law of evolution. It is perhaps this many-sidedness of Edison that has impressed the multitude, and that in the "popular vote" taken a couple of years ago by the New York Herald placed his name at the head of the list of ten greatest living Americans. It is curious and pertinent to note that a similar plebiscite taken by a technical journal among its expert readers had exactly the same result. Evidently the public does not agree with the opinion expressed by the eccentric artist Blake in his "Marriage of Heaven and Hell," when he said: "Improvement makes strange roads; but the crooked roads without improvements are roads of Genius."

The product of Edison's brain may be divided into three classes. The first embraces such arts and industries, or such apparatus, as have already been treated. The second includes devices like the tasimeter, phonomotor, odoroscope, etc., and others now to be noted. The third embraces a number of projected inventions, partially completed investigations, inventions in use but not patented, and a great many caveats filed in the Patent Office at various times during the last forty years for the purpose of protecting his ideas pending their contemplated realization in practice. These caveats served their purpose thoroughly in many instances, but there have remained a great variety of projects upon which no definite action was ever taken. One ought to add the contents of an unfinished piece of extraordinary fiction based wholly on new inventions and devices utterly unknown to mankind. Some day the novel may be finished, but Edison has no inclination to go back to it, and says he cannot under- stand how any man is able to make a speech or write a book, for he simply can't do it.

After what has been said in previous chapters, it will not seem so strange that Edison should have hundreds of dormant inventions on his hands. There are human limitations even for such a tireless worker as he is. While the preparation of data for this chapter was going on, one of the writers in discussing with him the vast array of unexploited things said: "Don't you feel a sense of regret in being obliged to leave so many things uncompleted?" To which he replied: "What's the use? One lifetime is too short, and I am busy every day improving essential parts of my established industries." It must suffice to speak briefly of a few leading inventions that have been worked out, and to dismiss with scant mention all the rest, taking just a few items, as typical and suggestive, especially when Edison can himself be quoted as to them. Incidentally it may be noted that things, not words, are referred to; for Edison, in addition to inventing the apparatus, has often had to coin the word to describe it. A large number of the words and phrases in modern electrical parlance owe their origin to him. Even the "call-word" of the telephone, "Hello!" sent tingling over the wire a few million times daily was taken from Menlo Park by men installing telephones in different parts of the world, men who had just learned it at the laboratory, and thus made it a universal sesame for telephonic conversation.

It is hard to determine where to begin with Edison's miscellaneous inventions, but perhaps telegraphy has the "right of line," and Edison's work in that field puts him abreast of the latest wireless developments that fill the world with wonder. "I perfected a system of train telegraphy between stations and trains in motion whereby messages could be sent from the moving train to the central office; and this was the forerunner of wireless telegraphy. This system was used for a number of years on the Lehigh Valley Railroad on their construction trains. The electric wave passed from a piece of metal on top of the car across the air to the telegraph wires; and then proceeded to the despatcher's office. In my first experiments with this system I tried it on the Staten Island Railroad, and employed an operator named King to do the experimenting. He reported results every day, and received instructions by mail; but for some reason he could send messages all right when the train went in one direction, but could not make it go in the contrary direction. I made suggestions of every kind to get around this phenomenon. Finally I telegraphed King to find out if he had any suggestions himself; and I received a reply that the only way he could propose to get around the difficulty was to put the island on a pivot so it could be turned around! I found the trouble finally, and the practical introduction on the Lehigh Valley road was the result. The system was sold to a very wealthy man, and he would never sell any rights or answer letters. He became a spiritualist subsequently, which probably explains it." It is interesting to note that Edison became greatly interested in the later developments by Marconi, and is an admiring friend and adviser of that well-known inventor.

The earlier experiments with wireless telegraphy at Menlo Park were made at a time when Edison was greatly occupied with his electric-light interests, and it was not until the beginning of 1886 that he was able to spare the time to make a public demonstration of the system as applied to moving trains. Ezra T. Gilliland, of Boston, had become associated with him in his experiments, and they took out several joint patents subsequently. The first practical use of the system took place on a thirteen-mile stretch of the Staten Island Railroad with the results mentioned by Edison above.

A little later, Edison and Gilliland joined forces with Lucius J. Phelps, another investigator, who had been experimenting along the same lines and had taken out several patents. The various interests were combined in a corporation under whose auspices the system was installed on the Lehigh Valley Railroad, where it was used for several years. The official demonstration trip on this road took place on October 6, 1887, on a six-car train running to Easton, Pennsylvania, a distance of fifty-four miles. A great many telegrams were sent and received while the train was at full speed, including a despatch to the "cable king," John Pender. London, England, and a reply from him.[17]

[17] Broadly described in outline, the system consisted of an induction circuit obtained by laying strips of tin along the top or roof of a railway car, and the installation of a special telegraph line running parallel with the track and strung on poles of only medium height. The train and also each signalling station were equipped with regulation telegraphic apparatus, such as battery, key, relay, and sounder, together with induction-coil and condenser. In addition, there was a transmitting device in the shape of a musical reed, or buzzer. In practice, this buzzer was continuously operated at high speed by a battery. Its vibrations were broken by means of a key into long and short periods, representing Morse characters, which were transmitted inductively from the train circuit to the pole line, or vice versa, and received by the operator at the other end through a high-resistance telephone receiver inserted in the secondary circuit of the induction-coil.

Although the space between the cars and the pole line was probably not more than about fifty feet, it is interesting to note that in Edison's early experiments at Menlo Park he succeeded in transmitting messages through the air at a distance of 580 feet. Speaking of this and of his other experiments with induction telegraphy by means of kites, communicating from one to the other and thus from the kites to instruments on the earth, Edison said recently: "We only transmitted about two and one-half miles through the kites. What has always puzzled me since is that I did not think of using the results of my experiments on `etheric force' that I made in 1875. I have never been able to understand how I came to overlook them. If I had made use of my own work I should have had long-distance wireless telegraphy."

In one of the appendices to this book is given a brief technical account of Edison's investigations of the phenomena which lie at the root of modern wireless or "space" telegraphy, and the attention of the reader is directed particularly to the description and quotations there from the famous note-books of Edison's experiments in regard to what he called "etheric force." It will be seen that as early as 1875 Edison detected and studied certain phenomena--i.e., the production of electrical effects in non-closed circuits, which for a time made him think he was on the trail of a new force, as there was no plausible explanation for them by the then known laws of electricity and magnetism. Later came the magnificent work of Hertz identifying the phenomena as "electromagnetic waves" in the ether, and developing a new world of theory and science based upon them and their production by disruptive discharges.

Edison's assertions were treated with scepticism by the scientific world, which was not then ready for the discovery and not sufficiently furnished with corroborative data. It is singular, to say the least, to note how Edison's experiments paralleled and proved in advance those that came later; and even his apparatus such as the "dark box" for making the tiny sparks visible (as the waves impinged on the receiver) bears close analogy with similar apparatus employed by Hertz. Indeed, as Edison sent the dark-box apparatus to the Paris Exposition in 1881, and let Batchelor repeat there the puzzling experiments, it seems by no means unlikely that, either directly or on the report of some friend, Hertz may thus have received from Edison a most valuable suggestion, the inventor aiding the physicist in opening up a wonderful new realm. In this connection, indeed, it is very interesting to quote two great authorities. In May, 1889, at a meeting of the Institution of Electrical Engineers in London, Dr. (now Sir) Oliver Lodge remarked in a discussion on a paper of his own on lightning conductors, embracing the Hertzian waves in its treatment: "Many of the effects I have shown--sparks in unsuspected places and other things--have been observed before. Henry observed things of the kind and Edison noticed some curious phenomena, and said it was not electricity but `etheric force' that caused these sparks; and the matter was rather pooh-poohed. It was a small part of THIS VERY THING; only the time was not ripe; theoretical knowledge was not ready for it." Again in his "Signalling without Wires," in giving the history of the coherer principle, Lodge remarks: "Sparks identical in all respects with those discovered by Hertz had been seen in recent times both by Edison and by Sylvanus Thompson, being styled `etheric force' by the former; but their theoretic significance had not been perceived, and they were somewhat sceptically regarded." During the same discussion in London, in 1889, Sir William Thomson (Lord Kelvin), after citing some experiments by Faraday with his insulated cage at the Royal Institution, said: "His (Faraday's) attention was not directed to look for Hertz sparks, or probably he might have found them in the interior. Edison seems to have noticed something of the kind in what he called `etheric force.' His name `etheric' may thirteen years ago have seemed to many people absurd. But now we are all beginning to call these inductive phenomena `etheric.' "With which testimony from the great Kelvin as to his priority in determining the vital fact, and with the evidence that as early as 1875 he built apparatus that demonstrated the fact, Edison is probably quite content.

It should perhaps be noted at this point that a curious effect observed at the laboratory was shown in connection with Edison lamps at the Philadelphia Exhibition of 1884. It became known in scientific parlance as the "Edison effect," showing a curious current condition or discharge in the vacuum of the bulb. It has since been employed by Fleming in England and De Forest in this country, and others, as the basis for wireless-telegraph apparatus. It is in reality a minute rectifier of alternating current, and analogous to those which have since been made on a large scale.

When Roentgen came forward with his discovery of the new "X"-ray in 1895, Edison was ready for it, and took up experimentation with it on a large scale; some of his work being recorded in an article in the Century Magazine of May, 1896, where a great deal of data may be found. Edison says with regard to this work: "When the X-ray came up, I made the first fluoroscope, using tungstate of calcium. I also found that this tungstate could be put into a vacuum chamber of glass and fused to the inner walls of the chamber; and if the X-ray electrodes were let into the glass chamber and a proper vacuum was attained, you could get a fluorescent lamp of several candle-power. I started in to make a number of these lamps, but I soon found that the X-ray had affected poisonously my assistant, Mr. Dally, so that his hair came out and his flesh commenced to ulcerate. I then concluded it would not do, and that it would not be a very popular kind of light; so I dropped it.

"At the time I selected tungstate of calcium because it was so fluorescent, I set four men to making all kinds of chemical combinations, and thus collected upward of 8000 different crystals of various chemical combinations, discovering several hundred different sub- stances which would fluoresce to the X-ray. So far little had come of X-ray work, but it added another letter to the scientific alphabet. I don't know any thing about radium, and I have lots of company." The Electrical Engineer of June 3, 1896, contains a photograph of Mr. Edison taken by the light of one of his fluorescent lamps. The same journal in its issue of April 1, 1896, shows an Edison fluoroscope in use by an observer, in the now familiar and universal form somewhat like a stereoscope. This apparatus as invented by Edison consists of a flaring box, curved at one end to fit closely over the forehead and eyes, while the other end of the box is closed by a paste- board cover. On the inside of this is spread a layer of tungstate of calcium. By placing the object to be observed, such as the hand, between the vacuum-tube and the fluorescent screen, the "shadow" is formed on the screen and can be observed at leisure. The apparatus has proved invaluable in surgery and has become an accepted part of the equipment of modern surgery. In 1896, at the Electrical Exhibition in the Grand Central Palace, New York City, given under the auspices of the National Electric Light Association, thousands and thousands of persons with the use of this apparatus in Edison's personal exhibit were enabled to see their own bones; and the resultant public sensation was great. Mr. Mallory tells a characteristic story of Edison's own share in the memorable exhibit: "The exhibit was announced for opening on Monday. On the preceding Friday all the apparatus, which included a large induction-coil, was shipped from Orange to New York, and on Saturday afternoon Edison, accompanied by Fred Ott, one of his assistants, and myself, went over to install it so as to have it ready for Monday morning. Had everything been normal, a few hours would have sufficed for completion of the work, but on coming to test the big coil, it was found to be absolutely out of commission, having been so seriously injured as to necessitate its entire rewinding. It being summer-time, all the machine shops were closed until Monday morning, and there were several miles of wire to be wound on the coil. Edison would not consider a postponement of the exhibition, so there was nothing to do but go to work and wind it by hand. We managed to find a lathe, but there was no power; so each of us, including Edison, took turns revolving the lathe by pulling on the belt, while the other two attended to the winding of the wire. We worked continuously all through that Saturday night and all day Sunday until evening, when we finished the job. I don't remember ever being conscious of more muscles in my life. I guess Edison was tired also, but he took it very philosophically." This was apparently the first public demonstration of the X-ray to the American public.

Edison's ore-separation work has been already fully described, but the story would hardly be complete without a reference to similar work in gold extraction, dating back to the Menlo Park days: "I got up a method," says Edison, "of separating placer gold by a dry process, in which I could work economically ore as lean as five cents of gold to the cubic yard. I had several car-loads of different placer sands sent to me and proved I could do it. Some parties hearing I had succeeded in doing such a thing went to work and got hold of what was known as the Ortiz mine grant, twelve miles from Santa Fe, New Mexico. This mine, according to the reports of several mining engineers made in the last forty years, was considered one of the richest placer deposits in the United States, and various schemes had been put forward to bring water from the mountains forty miles away to work those immense beds. The reports stated that the Mexicans had been panning gold for a hundred years out of these deposits.

"These parties now made arrangements with the stockholders or owners of the grant, and with me, to work the deposits by my process. As I had had some previous experience with the statements of mining men, I concluded I would just send down a small plant and prospect the field before putting up a large one. This I did, and I sent two of my assistants, whom I could trust, down to this place to erect the plant; and started to sink shafts fifty feet deep all over the area. We soon learned that the rich gravel, instead of being spread over an area of three by seven miles, and rich from the grass roots down, was spread over a space of about twenty-five acres, and that even this did not average more than ten cents to the cubic yard. The whole placer would not give more than one and one- quarter cents per cubic yard. As my business arrangements had not been very perfectly made, I lost the usual amount."

Going to another extreme, we find Edison grappling with one of the biggest problems known to the authorities of New York--the disposal of its heavy snows. It is needless to say that witnessing the ordinary slow and costly procedure would put Edison on his mettle. "One time when they had a snow blockade in New York I started to build a machine with Batchelor--a big truck with a steam-engine and compressor on it. We would run along the street, gather all the snow up in front of us, pass it into the compressor, and deliver little blocks of ice behind us in the gutter, taking one- tenth the room of the snow, and not inconveniencing anybody. We could thus take care of a snow-storm by diminishing the bulk of material to be handled. The preliminary experiment we made was dropped because we went into other things. The machine would go as fast as a horse could walk."

Edison has always taken a keen interest in aerial flight, and has also experimented with aeroplanes, his preference inclining to the helicopter type, as noted in the newspapers and periodicals from time to time. The following statement from him refers to a type of aeroplane of great novelty and ingenuity: "James Gordon Bennett came to me and asked that I try some primary experiments to see if aerial navigation was feasible with `heavier-than-air' machines. I got up a motor and put it on the scales and tried a large number of different things and contrivances connected to the motor, to see how it would lighten itself on the scales. I got some data and made up my mind that what was needed was a very powerful engine for its weight, in small compass. So I conceived of an engine employing guncotton. I took a lot of ticker paper tape, turned it into guncotton and got up an engine with an arrangement whereby I could feed this gun- cotton strip into the cylinder and explode it inside electrically. The feed took place between two copper rolls. The copper kept the temperature down, so that it could only explode up to the point where it was in contact with the feed rolls. It worked pretty well; but once the feed roll didn't save it, and the flame went through and exploded the whole roll and kicked up such a bad explosion I abandoned it. But the idea might be made to work."

Turning from the air to the earth, it is interesting to note that the introduction of the underground Edison system in New York made an appeal to inventive ingenuity and that one of the difficulties was met as follows: "When we first put the Pearl Street station in operation, in New York, we had cast-iron junction- boxes at the intersections of all the streets. One night, or about two o'clock in the morning, a policeman came in and said that something had exploded at the corner of William and Nassau streets. I happened to be in the station, and went out to see what it was. I found that the cover of the manhole, weighing about 200 pounds, had entirely disappeared, but everything inside was intact. It had even stripped some of the threads of the bolts, and we could never find that cover. I concluded it was either leakage of gas into the manhole, or else the acid used in pickling the casting had given off hydrogen, and air had leaked in, making an explosive mixture. As this was a pretty serious problem, and as we had a good many of the manholes, it worried me very much for fear that it would be repeated and the company might have to pay a lot of damages, especially in districts like that around William and Nassau, where there are a good many people about. If an explosion took place in the daytime it might lift a few of them up. However, I got around the difficulty by putting a little bottle of chloroform in each box, corked up, with a slight hole in the cork. The chloroform being volatile and very heavy, settled in the box and displaced all the air. I have never heard of an explosion in a manhole where this chloroform had been used. Carbon tetrachloride, now made electrically at Niagara Falls, is very cheap and would be ideal for the purpose."

Edison has never paid much attention to warfare, and has in general disdained to develop inventions for the destruction of life and property. Some years ago, however, he became the joint inventor of the Edison- Sims torpedo, with Mr. W. Scott Sims, who sought his co-operation. This is a dirigible submarine torpedo operated by electricity. In the torpedo proper, which is suspended from a long float so as to be submerged a few feet under water, are placed the small electric motor for propulsion and steering, and the explosive charge. The torpedo is controlled from the shore or ship through an electric cable which it pays out as it goes along, and all operations of varying the speed, reversing, and steering are performed at the will of the distant operator by means of currents sent through the cable. During the Spanish-American War of 1898 Edison suggested to the Navy Department the adoption of a compound of calcium carbide and calcium phosphite, which when placed in a shell and fired from a gun would explode as soon as it struck water and ignite, producing a blaze that would continue several minutes and make the ships of the enemy visible for four or five miles at sea. Moreover, the blaze could not be extinguished.

Edison has always been deeply interested in "conservation," and much of his work has been directed toward the economy of fuel in obtaining electrical energy directly from the consumption of coal. Indeed, it will be noted that the example of his handwriting shown in these volumes deals with the importance of obtaining available energy direct from the combustible without the enormous loss in the intervening stages that makes our best modern methods of steam generation and utilization so barbarously extravagant and wasteful. Several years ago, experimenting in this field, Edison devised and operated some ingenious pyromagnetic motors and generators, based, as the name implies, on the direct application of heat to the machines. The motor is founded upon the principle discovered by the famous Dr. William Gilbert--court physician to Queen Elizabeth, and the Father of modern electricity--that the magnetic properties of iron diminish with heat. At a light-red heat, iron becomes non-magnetic, so that a strong magnet exerts no influence over it. Edison employed this peculiar property by constructing a small machine in which a pivoted bar is alternately heated and cooled. It is thus attracted toward an adjacent electromagnet when cold and is uninfluenced when hot, and as the result motion is produced.

The pyromagnetic generator is based on the same phenomenon; its aim being of course to generate electrical energy directly from the heat of the combustible. The armature, or moving part of the machine, consists in reality of eight separate armatures all constructed of corrugated sheet iron covered with asbestos and wound with wire. These armatures are held in place by two circular iron plates, through the centre of which runs a shaft, carrying at its lower extremity a semicircular shield of fire-clay, which covers the ends of four of the armatures. The heat, of whatever origin, is applied from below, and the shaft being revolved, four of the armatures lose their magnetism constantly, while the other four gain it, so to speak. As the moving part revolves, therefore, currents of electricity are set up in the wires of the armatures and are collected by a commutator, as in an ordinary dynamo, placed on the upper end of the central shaft.

A great variety of electrical instruments are included in Edison's inventions, many of these in fundamental or earlier forms being devised for his systems of light and power, as noted already. There are numerous others, and it might be said with truth that Edison is hardly ever without some new device of this kind in hand, as he is by no means satisfied with the present status of electrical measurements. He holds in general that the meters of to-day, whether for heavy or for feeble currents, are too expensive, and that cheaper instruments are a necessity of the times. These remarks apply more particularly to what may be termed, in general, circuit meters. In other classes Edison has devised an excellent form of magnetic bridge, being an ingenious application of the principles of the familiar Wheatstone bridge, used so extensively for measuring the electrical resistance of wires; the testing of iron for magnetic qualities being determined by it in the same way. Another special instrument is a "dead beat" galvanometer which differs from the ordinary form of galvanometer in having no coils or magnetic needle. It depends for its action upon the heating effect of the current, which causes a fine platinum-iridium wire enclosed in a glass tube to expand; thus allowing a coiled spring to act on a pivoted shaft carrying a tiny mirror. The mirror as it moves throws a beam of light upon a scale and the indications are read by the spot of light. Most novel of all the apparatus of this measuring kind is the odoroscope, which is like the tasimeter described in an earlier chapter, except that a strip of gelatine takes the place of hard rubber, as the sensitive member. Besides being affected by heat, this device is exceedingly sensitive to moisture. A few drops of water or perfume thrown on the floor of a room are sufficient to give a very decided indication on the galvanometer in circuit with the instrument. Barometers, hygrometers, and similar instruments of great delicacy can be constructed on the principle of the odoroscope; and it may also be used in determining the character or pressure of gases and vapors in which it has been placed.

In the list of Edison's patents at the end of this work may be noted many other of his miscellaneous inventions, covering items such as preserving fruit in vacuo, making plate-glass, drawing wire, and metallurgical processes for treatment of nickel, gold, and copper ores; but to mention these inventions separately would trespass too much on our limited space here. Hence, we shall leave the interested reader to examine that list for himself.

From first to last Edison has filed in the United States Patent Office--in addition to more than 1400 applications for patents--some 120 caveats embracing not less than 1500 inventions. A "caveat" is essentially a notice filed by an inventor, entitling him to receive warning from the Office of any application for a patent for an invention that would "interfere" with his own, during the year, while he is supposed to be perfecting his device. The old caveat system has now been abolished, but it served to elicit from Edison a most astounding record of ideas and possible inventions upon which he was working, and many of which he of course reduced to practice. As an example of Edison's fertility and the endless variety of subjects engaging his thoughts, the following list of matters covered by ONE caveat is given. It is needless to say that all the caveats are not quite so full of "plums," but this is certainly a wonder.

Forty-one distinct inventions relating to the phonograph, covering various forms of recorders, arrangement of parts, making of records, shaving tool, adjustments, etc.

Eight forms of electric lamps using infusible earthy oxides and brought to high incandescence in vacuo by high potential current of several thousand volts; same character as impingement of X-rays on object in bulb.

A loud-speaking telephone with quartz cylinder and beam of ultra-violet light.

Four forms of arc light with special carbons.

A thermostatic motor.

A device for sealing together the inside part and bulb of an incandescent lamp mechanically.

Regulators for dynamos and motors.

Three devices for utilizing vibrations beyond the ultra violet.

A great variety of methods for coating incandescent lamp filaments with silicon, titanium, chromium, osmium, boron, etc.

Several methods of making porous filaments.

Several methods of making squirted filaments of a variety of materials, of which about thirty are specified.

Seventeen different methods and devices for separating magnetic ores.

A continuously operative primary battery.

A musical instrument operating one of Helmholtz's artificial larynxes.

A siren worked by explosion of small quantities of oxygen and hydrogen mixed.

Three other sirens made to give vocal sounds or articulate speech.

A device for projecting sound-waves to a distance without spreading and in a straight line, on the principle of smoke rings.

A device for continuously indicating on a galvanometer the depths of the ocean.

A method of preventing in a great measure friction of water against the hull of a ship and incidentally preventing fouling by barnacles.

A telephone receiver whereby the vibrations of the diaphragm are considerably amplified.

Two methods of "space" telegraphy at sea.

An improved and extended string telephone.

Devices and method of talking through water for considerable distances.

An audiphone for deaf people.

Sound-bridge for measuring resistance of tubes and other materials for conveying sound.

A method of testing a magnet to ascertain the existence of flaws in the iron or steel composing the same.

Method of distilling liquids by incandescent conductor immersed in the liquid.

Method of obtaining electricity direct from coal.

An engine operated by steam produced by the hydration and dehydration of metallic salts.

Device and method for telegraphing photographically.

Carbon crucible kept brilliantly incandescent by current in vacuo, for obtaining reaction with refractory metals.

Device for examining combinations of odors and their changes by rotation at different speeds.

From one of the preceding items it will be noted that even in the eighties Edison perceived much advantage to be gained in the line of economy by the use of lamp filaments employing refractory metals in their construction. From another caveat, filed in 1889, we extract the following, which shows that he realized the value of tungsten also for this purpose. "Filaments of carbon placed in a combustion tube with a little chloride ammonium. Chloride tungsten or titanium passed through hot tube, depositing a film of metal on the carbon; or filaments of zirconia oxide, or alumina or magnesia, thoria or other infusible oxides mixed or separate, and obtained by moistening and squirting through a die, are thus coated with above metals and used for incandescent lamps. Osmium from a volatile compound of same thus deposited makes a filament as good as carbon when in vacuo."

In 1888, long before there arose the actual necessity of duplicating phonograph records so as to produce replicas in great numbers, Edison described in one of his caveats a method and process much similar to the one which was put into practice by him in later years. In the same caveat he describes an invention whereby the power to indent on a phonograph cylinder, instead of coming directly from the voice, is caused by power derived from the rotation or movement of the phonogram surface itself. He did not, however, follow up this invention and put it into practice. Some twenty years later it was independently invented and patented by another inventor. A further instance of this kind is a method of telegraphy at sea by means of a diaphragm in a closed port-hole flush with the side of the vessel, and actuated by a steam-whistle which is controlled by a lever, similarly to a Morse key. A receiving diaphragm is placed in another and near-by chamber, which is provided with very sensitive stethoscopic ear-pieces, by which the Morse characters sent from another vessel may be received. This was also invented later by another inventor, and is in use to-day, but will naturally be rivalled by wireless telegraphy. Still another instance is seen in one of Edison's caveats, where he describes a method of distilling liquids by means of internally applied heat through electric conductors. Although Edison did not follow up the idea and take out a patent, this system of distillation was later hit upon by others and is in use at the present time.

In the foregoing pages of this chapter the authors have endeavored to present very briefly a sketchy notion of the astounding range of Edison's practical ideas, but they feel a sense of impotence in being unable to deal adequately with the subject in the space that can be devoted to it. To those who, like the authors, have had the privilege of examining the voluminous records which show the flights of his imagination, there comes a feeling of utter inadequacy to convey to others the full extent of the story they reveal.

The few specific instances above related, although not representing a tithe of Edison's work, will probably be sufficient to enable the reader to appreciate to some extent his great wealth of ideas and fertility of imagination, and also to realize that this imagination is not only intensely practical, but that it works prophetically along lines of natural progress.