stimulus of that dread. “When I’m a man, I shall make

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

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