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.