The application of the magnet to the machines for electric lighting will be shown further on. Very powerful currents are obtained by the induction coil; but the currents would not be of practical service were it not for the apparatus called a Commutator, or key, which reverses the connection of the bobbins, and turns the current at every half revolution. Just as if a current were being sent across and back over a table, and when the current has reached the end, an instantaneous wheel round, or pivoting of the table, sends the current on, in continuation (but on the table all the time), because of the sudden change of its position. The back rush being on the table, the movement of the latter really makes the line continuous, and by quickly breaking and reversing the current in the commutator, the effect is gained in the machine.
Electro-magnets and bobbin, etc. (Clarke’s machine)
CHAPTER XXII.
SUNDRY ELECTRICAL APPLIANCES—MR. EDISON’S INVENTIONS—THE ELECTRIC LIGHT—THE GYROSCOPE—A NEW ELECTROPHORUS—ELECTRIC TOYS.
The Electro-Motograph—although perhaps even yet scarcely developed—has already proved a very useful invention. The idea of it first occurred to Mr. Edison in 1873, when he was prosecuting some researches in chemical telegraphy. “One day,” says Mr. Fox, in his account of the invention, “as he sat pondering over his work, he happened to take in hand the metallic point through which, as it rested upon the paper, the current was wont to pass. When again he closed the circuit to let the current through the paper, he held the metallic point loosely, and unintentionally allowed it to rest upon the paper. Every time he moved the metallic strip on the paper the latter became wonderfully smooth. Edison was determined to find the reason of this, and he decided that the electricity very much lessened the friction of the metal on the paper. He made many experiments, and brought the subject before the Royal Society in 1874, but nothing came of the idea till 1876, when Edison was perfecting his musical telephone.
“The new appliance is, in fact, the same invention revived and now perfected by the original inventor, and brought to complete practical success under the title of the ‘electro-motograph.’ The action of the ‘electro-motograph’ depends on the fact, discovered during former experiments, and employed imperfectly in the musical telephone, that the friction of moving bodies varies in greater or less degree with their electrical condition. In the electro-motograph a cylinder made of prepared chalk, and saturated with a strong solution of caustic alkali, is set upon supports, so that it can be turned upon its axis. A strip of metal fastened to the mica diaphragm rests on the cylinder, and is pressed so firmly by its spring upon the cylinder that when it is turned by means of the handle the friction of the strip on the cylinder tends to pull the diaphragm out of shape, causing it to bulge inward as long as the cylinder is in motion. If now, while this motion of the cylinder is maintained, an electric current passes through the strip of metal, and then through the chalk cylinder to earth, the amount of this friction is varied or it is destroyed altogether, and the strip slides freely on the cylinder. This was the basis of the former invention. The release from friction by a change in electric condition in the first instrument failed simply from ignorance of some slight matters of detail, that in the electro-motograph are corrected and made practical. In the musical telephone the releasing of the frictional resistance by electric action caused the sounding-board of a guitar to vibrate, and thus set up sonorous vibrations. In the electro-motograph the mica disc takes the place of the guitar, and, by the improved construction of the apparatus, intricate and complex vibrations, such as are produced in speaking, are reproduced in their original or even in greater volume. When the apparatus is at rest the diaphragm is motionless, and electric currents shot through the apparatus produce no effect. In the same manner the mere turning of the cylinder without electric action produces no effect, except to pull the diaphragm slightly out of shape. If while the cylinder is being turned an electric impulse arrives, the pull on the diaphragm, caused by the friction of the strip on the cylinder, is more or less released, and the diaphragm is free to vibrate or spring back into its original condition. If now, the electric impulses follow one another in regular order in correspondence with the sonorous vibrations imparted to the transmitting telephone, the alternate slipping and catching of the metal strip on the cylinder will follow in the same order, and thus the diaphragm will be made to vibrate in unison with the original vibrations, and thus reproduce the original words. As the mica disc is much larger than the disc of the transmitting instrument, the amplitude of its swing may be much greater, and consequently it will repeat the words with greater power. The electro-motograph is practically an apparatus for transforming electric action received from a distance into mechanical work. The amount of electric action has nothing to do with the amount of the mechanical work performed, because the movement of the cylinder is controlled by power independently of the electric action, the electricity merely releasing this power by destroying the friction in greater or less degree. The electric action set up by the sonorous vibrations at the transmitting end of the line may be very slight, while the mechanical action at the distant end may be powerful, and in this manner the amplitude of the vibrations may be increased to an indefinite extent, and a whisper may reappear as a loud shout.
“The electro-motograph is not only a solution of the telephone, making it capable of sounds of every quality and pitch and in greatly increased volume, but by this conversion of electrical action into mechanical work at a distance makes it possible to unite the telephone and phonograph. Telephonic messages by the electro-motograph may be impressed upon a self-acting (clock-work) phonograph, the same current starting and stopping the phonograph after the manner of the stock-reporting machines, and afterward the phonograph may be made to repeat the message impressed upon it.”