Part 7 (2/2)
The induction balance has been used as a ”Sonometer” for measuring the sense of hearing, and also for telling base coins. The writer devised a form of it for ”divining” the presence of gold and metallic ores which has been applied by Captain M'Evoy in his ”submarine detector” for exploring the sea bottom for lost anchors and sunken treasure. When President Garfield was shot, the position of the bullet was ascertained by a similar arrangement.
The microphone as a means of magnifying feeble sounds has been employed for localising the leaks in water pipes and in medical examinations. Some years ago it saved a Russian lady from premature burial by rendering the faint beating of her heart audible.
Edison's electric pen is useful in copying letters. It works by puncturing a row of minute holes along the lines of the writing, and thus producing a stencil plate, which, when placed over a clean sheet of paper and brushed with ink, gives a duplicate of the writing by the ink penetrating the holes to the paper below.
It is ill.u.s.trated in figure 93, where P is the pen, consisting of a hollow stem in which a fine needle actuated by the armature of a small electromagnet plies rapidly up and down and pierces the paper. The current is derived from a small battery B, and an inking roller like that used in printing serves to apply the ink.
In 1878 Mr. Edison announced his invention of a machine for the storage and reproduction of speech, and the announcement was received with a good deal of incredulity, notwithstanding the partial success of Faber and others in devising mechanical articulators. The simplicity of Edison's invention when it was seen and heard elicited much admiration, and although his first instrument was obviously imperfect, it was nevertheless regarded as the germ of something better. If the words spoken into the instrument were heard in the first place, the likeness of the reproduction was found to be unmistakable. Indeed, so faithful was the replica, that a member of the Academy of Sciences, Paris, stoutly maintained that it was due to ventriloquism or some other trickery. It was evident, however, that before the phonograph could become a practical instrument, further improvements in the nicety of its articulation were required. The introduction of the electric light diverted Mr. Edison from the task of improving it, although he does not seem to have lost faith in his pet invention.
During the next ten years he acc.u.mulated a large fortune, and was the princ.i.p.al means of introducing both electric light and power to the world at large. This done, however, he returned to his earlier love, and has at length succeeded in perfecting it so as to redeem his past promises and fulfill his hopes regarding it.
The old instrument consisted, as is well known, of a vibrating tympan or drum, from the centre of which projected a steel point or stylus, in such a manner that on speaking to the tympan its vibrations would urge the stylus to dig into a sheet of tinfoil moving past its point. The foil was supported on a grooved barrel, so that the hollow of the groove behind it permitted the foil to give under the point of the stylus, and take a corrugated or wavy surface corresponding to the vibrations of the speech. Thus recorded on a yielding but somewhat stiff material, these undulations could be preserved, and at a future time made to deflect the point of a similar stylus, and set a corresponding diaphragm or tympan into vibration, so as to give out the original sounds, or an imitation of them.
Tinfoil, however, is not a very satisfactory material on which to receive the vibrations in the first place. It does not precisely respond to the movements of the marking stylus in taking the impression, and does not guide the receiving stylus sufficiently well in reproducing sounds. Mr. Edison has therefore adopted wax in preference to it; and instead of tinfoil spread on a grooved support, he now employs a cylinder of wax to take the print of the vibrations. Moreover, he no longer uses the same kind of diaphragm to print and receive the sounds, but employs a more delicate one for receiving them. The marking cylinder is now kept in motion by an electric motor, instead of by hand-turning, as in the earlier instrument.
The new phonograph, which we ill.u.s.trate in figure 94, is about the size of an ordinary sewing machine, and is of exquisite workmans.h.i.+p, the performance depending to a great extent on the perfection and fitness of the mechanism. It consists of a horizontal spindle S, carrying at one end the wax cylinder C, on which the sonorous vibrations are to be imprinted. Over the cylinder is supported a diaphragm or tympan T, provided with a conical mouthpiece M for speaking into. Under the tympan there is a delicate needle or stylus, with its point projecting from the centre of the tympan downwards to the surface of the wax cylinder, so that when a person speaks into the mouthpiece, the voice vibrates the tympan and drives the point of the stylus down into the wax, making an imprint more or less deep in accordance with the vibrations of the voice. The cylinder is kept revolving in a spiral path, at a uniform speed, by means of an electric motor E, fitted with a sensitive regulator and situated at the base of the machine. The result is that a delicate and ridgy trace is cut in the surface of wax along a spiral line. This is the sound record, and by subst.i.tuting a finer tympan for the one used in producing it, the ridges and inequalities of the trace can be made to agitate a light stylus resting on them, and cause it to set the delicate tympan into vibrations corresponding very accurately to those of the original sounds. The tympan employed for receiving is made of gold-beater's skin, having a stud at its centre and a springy stylus of steel wire. The sounds emitted by this device are almost a whisper as compared to the original ones, but they are faithful in articulation, which is the main object, and they are conveyed to the ear by means of flexible hearing-tubes.
These tympans are interchangeable at will, and the arm which carries them is also provided with a turning tool for smoothing the wax cylinder prior to its receiving the print. The cylinders are made of different sizes, from 1 to 8 inches long and 4 inches in diameter. The former has a storage capacity of 200 words. The next in size has twice that, or 400 words, and so on. Mr. Edison states that four of the large 8-inch cylinders can record all ”Nicholas Nickleby,” which could therefore be automatically read to a private invalid or to a number of patients in a hospital simultaneously, by means of a bunch of hearing-tubes. The cylinders can be readily posted like letters, and made to deliver their contents viva voce in a duplicate phonograph, every tone and expression of the writer being rendered with more or less fidelity. The phonograph has proved serviceable in recording the languages and dialects of vanis.h.i.+ng races, as well as in teaching p.r.o.nunciation.
The dimensions, form, and consequent appearance of the present commercial American phonograph are quite different from that above described, but the underlying principles and operations are identical.
A device for lighting gas by the electric spark is shown in figure 95, where A is a flat vulcanite box, containing the apparatus which generates the electricity, and a stem or pointer L, which applies the spark to the gas jet. The generator consists of a small ”influence” machine, which is started by pressing the thumb- key C on the side of the box. The rotation of a disc inside the box produces a supply of static electricity, which pa.s.ses in a stream of sparks between two contact-points in the open end of the stem D. The latter is tubular, and contains a wire insulated from the metal of the tube, and forming with the tube the circuit for the electric discharge. The handle enables the contrivance to be readily applied. The apparatus is one of the few successful practical applications of static electricity.
Other electric gas-lighters consist of metal points placed on the burner, so that the electric spark from a small induction coil or dynamo kindles the jet.
A platinum wire made white-hot by the pa.s.sage of a current is sometimes used to light lamps, as shown in figure 96, where W is a small spiral of platinum connected in circuit with a generator by the terminals T T. When the lamp L is pressed against the b.u.t.ton B the wire glows and lights it.
Explosives, such as gunpowder and guncotton, are also ignited by the electric spark from an induction coil or the incandescence of a wire. Figure 97 shows the interior of an ordinary electric fuse for blasting or exploding underground mines. It consists of a box of wood or metal primed with gunpowder or other explosive, and a platinum wire P soldered to a pair of stout copper wires W, insulated with gutta-percha. When the current is sent along these wires, the platinum glows and ignites the explosive. Detonating fuses are primed with fulminate of mercury.
Springs for watches and other purposes are tempered by heating them with the current and quenching them in a bath of oil.
Electrical cautery is performed with an incandescent platinum wire in lieu of the knife, especially for such operations as the removal of the tongue or a tumour.
It was known to the ancients that a fish called a torpedo existed in the Mediterranean which was capable of administering a shock to persons and benumbing them. The torpedo, or ”electric ray,” is found in the Atlantic as well as the Mediterranean, and is allied to the skate. It has an electric organ composed of 800 or 1000 polygonal cells in its head, and the discharge, which appears to be a vibratory current, pa.s.ses from the back or positive pole to the belly or negative pole through the water. The gymotus, or Surinam eel, which attains a length of five or six feet, has an electric organ from head to tail, and can give a shock sufficient to kill a man. Humboldt has left a vivid picture of the frantic struggles of wild horses driven by the Indians of Venezuela into the ponds of the savannahs infested by these eels, in order to make them discharge their thunderbolts and be readily caught.
Other fishes--the silurus, malapterurus, and so on--are likewise endowed with electric batteries for stunning and capturing their prey. The action of the organs is still a mystery, as, indeed, is the whole subject of animal electricity. n.o.bili and Matteucci discovered that feeble currents are generated by the excitation of the nerves and the contraction of the muscles in the human subject.
Electricity promises to become a valuable remedy, and currents-- continuous, intermittent, or alternating--are applied to the body in nervous and muscular affections with good effect; but this should only be done under medical advice, and with proper apparatus.
In many cases of severe electric shock or lightning stroke, death is merely apparent, and the person may be brought back to life by the method of artificial respiration and rhythmic traction of the tongue, as applied to the victims of drowning or dead faint.
A good lightning conductor should not have a higher electrical resistance than 10 ohms from the point to the ground, including the ”earth” contact. Exceptionally good conductors have only about 5 ohms. A high resistance in the rod is due either to a flaw in the conductor or a bad earth connection, and in such a case the rod may be a source of danger instead of security, since the discharge is apt to find its way through some part of the building to the ground, rather than entirely by the rod. It is, therefore, important to test lightning conductors from time to time, and the magneto-electric tester of Siemens, which we ill.u.s.trate in figures 98 and 99, is very serviceable for the purpose, and requires no battery. The apparatus consists of a magneto-electric machine AT, which generates the testing current by turning a handle, and a Wheatstone bridge. The latter comprises a ring of German silver wire, forming two branches. A contact lever P moves over the ring, and is used as a battery key. A small galvanometer G shows the indications of the testing current. A bra.s.s sliding piece S puts the galvanometer needle in and out of action. There are also several connecting terminals, b b', l, &c., and a comparison resistance R (figure 98). A small key K is fixed to the terminal l (figure 99), and used to put the current on the lightning-rod, or take it off at will. A leather bag A at one side of the wooden case (figure 99) holds a double conductor leading wire, which is used for connecting the magneto-electric machine to the bridge. On turning the handle of M the current is generated, and on closing the key K it circulates from the terminals of the machine through the bridge and the lightning-rod joined with the latter. The needle of the galvanometer is deflected by it, until the resistance in the box R is adjusted to balance that in the rod.
When this is so, the galvanometer needle remains at rest. In this way the resistance of the rod is told, and any change in it noted.
In order to effect the test, it is necessary to have two earth plates, E1 and E2, one (El) that of the rod, and the other (E2) that for connecting to the testing apparatus by the terminal b1 (figure 99). The whole instrument only weighs about 9 lbs. In order to test the ”earth” alone, a copper wire should be soldered to the rod at a convenient height above the ground, and terminal screws fitted to it, as shown at T (figure 99), so that instead of joining the whole rod in circuit with the apparatus, only that part from T downwards is connected. The Hon. R. Abercrombie has recently drawn attention to the fact that there are three types of thunderstorm in Great Britain. The first, or squall thunderstorms, are squalls a.s.sociated with thunder and lightning. They form on the sides of primary cyclones. The second, or commonest thunderstorms, are a.s.sociated with secondary cyclones, and are rarely accompanied by squalls The third, or line thunderstorms, take the form of narrow bands of rain and thunder--for example, 100 miles long by 5 to 10 miles broad. They cross the country rapidly, and nearly broadside on. These are usually preceded by a violent squall, like that which capsized the Eurydice.
The gloom of January, 1896, with its war and rumours of war, was, at all events, relieved by a single bright spot. Electricity has surprised the world with a new marvel, which confirms her t.i.tle to be regarded as the most miraculous of all the sciences. Within the past twenty years she has given us the telephone of Bell, enabling London to speak with Paris, and Chicago with New York; the microphone of Hughes, which makes the tread of a fly sound like the ”tramp of an elephant,” as Lord Kelvin has said; the phonograph of Edison, in which we can hear again the voices of the dead; the electric light which glows without air and underwater, electric heat without fire, electric power without fuel, and a great deal more beside. To these triumphs we must now add a means of photographing unseen objects, such as the bony skeletons in the living body, and so revealing the invisible.
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