The Telegraph.—The telegraph is nothing but a magnet at each end of a wire, with a lever for an armature, which opens and closes the circuit that passes through the magnets and armature, so that an impulse on the lever, or armature, at one end, by making and breaking the circuit, also makes and breaks the circuit at the other end.
Telephone.—The telephone has merely a disk close to but not touching the end of a magnet. The sonorous vibration of the voice oscillates the diaphragm, and as the diaphragm is in the magnetic field of the magnet, it varies the pressure, so called, causing the diaphragm at the other end of the wire to vibrate in unison and give out the same sound originally imparted to the other diaphragm.
Transmitter.—The transmitter is merely a sen[p. 154]sitized instrument. It depends solely on the principle of light contact points in an electric circuit, whereby the vibrations of the voice are augmented.
Phonograph.—The phonograph is not an electrical instrument. It has a diaphragm provided centrally with a blunt pin, or stylus. To make the record, some soft or plastic material, like wax, or tinfoil, is caused to move along so that the point of the stylus makes impressions in it, and the vibrations of the diaphragm cause the point to traverse a groove of greater or smaller indentations. When this groove is again presented to the stylus the diaphragm is vibrated and gives forth the sounds originally imparted to it when the indentations were made.
Wireless Telegraphy.—Wireless telegraphy depends for its action on what is called induction. Through this property a current is made of a high electro-motive force, which means of a high voltage, and this disturbs the ether with such intensity that the waves are sent out in all directions to immense distances.
The great discovery has been to find a mechanism sensitive enough to detect the induction waves. The instrument for this purpose is called a coherer, in which small particles cohere through the action of the electric waves, and are caused to fall apart mechanically, during the electrical impulses
Printing Telegraph.—The printing telegraph requires the synchronous turning of two wheels. This means that two wheels at opposite ends of a wire must be made to turn at exactly the same rate of speed. Originally, this was tried by clock work, but without success commercially, for the reason that a pendulum does not beat with the same speed at the equator, as at different latitudes, nor at altitudes; and temperature also affects the rate. The solution was found by making the two wheels move by means of a timing fork, which vibrates with the same speed everywhere, and under all conditions.
Electric Motor.—The direct current electric motor depends for its action on the principle that likes repel, and unlikes attract. The commutator so arranges the poles that at the proper points, in the revolution of the armature, the poles are always presented to each other in such a way that as they approach each other, they are opposites, and thus attract, and as they recede from each other they repel. A dynamo is exactly the same, except that the commutator reverses the operation and makes the poles alike as they approach each other, and unlike as they recede.
Steel is simply iron, to which has been added a small per cent of carbon.