CHAPTER I. INTRODUCTORY: WIRELESS TRANSMISSION AND RECEPTION. THE ETHER. ELECTRICAL OSCILLATIONS. ELECTROMAGNETIC WAVES.Wireless telegraphy, that marvelous art which has made possible the instantaneous transmission of intelligence between widely distant parts having no apparent physical connection save that of the earth, air, and water, is one of those wonders of science which appeal to the average mind as either incomprehensible or only explainable through the use of highly technical language. Contrary to this general opinion, however, the whole theory and practice of the wireless transmission of messages is capable of the simplest explanation.FIG. 1.—Throw a stone into a pool of water and little waves will radiate from the spot where the stone struck.FIG. 1.—Throw a stone into a pool of water and little waves will radiate from the spot where the stone struck.Throw a stone into a pool of water. A disturbance is immediately created, and little waves will radiate from the spot where the stone struck the water, gradually spreading out into enlarging circles until they reach the shores or die away. By throwing several stones in succession with varying intervals between them it would be possible to so arrange a set of signals that they would convey a meaning to one who is initiated, standing on the opposite side of the pool. The little waves are the vehicle which transmits the intelligence, and the water themediumin which the waves travel.Wireless telegraph instruments are simply a means forcreating and detecting waves in a great pool of ether.Scientists suppose that all space and matter is pervaded with a hypotheticalmediumof extreme tenuity and elasticity, calledluminiferous ether, or simplyether.Although ether is invisible, odorless, and practically weightless, it is not merely the fantastic creation of speculative philosophers, but is as essential to our existence as the air we breathe and the food we eat. By imagining and accepting its reality, it is possible to explain and understand many scientific puzzles. The universe is a vast pool of ether. It is all-pervading. There is no void. It is diffused even among the molecules of which solid bodies are composed. The study of this substance is, perhaps, one of the most fascinating and important duties of the physicist.Ninety million miles away from our earth is a huge flaming body of vapors and gases, called the sun. This seething mass of flame and heat furnishes us more than mere winter and summer and night and day, for we on this earth are not living on our own resources, and the real work of the world so necessary for even bare existence is accomplished by the energy of the sun stored up in coal, in plants and trees and mountain torrents.Light is known to be vibrations of an extremely rapid period—electromagnetic waves, they are called. Heat can be shown to be of the same nature. Traveling at the rate of over 180,000 miles per second, these two great gifts of the sun come streaming continually down to us over the inconceivable distance of almost 100,000,000 miles. Both require a medium for their propagation. The ether supplies it. It is the substance with which the universe is filled. Incidentally it is also the seat of all electrical and magnetic forces.FIG. 2.—A Leyden jar is a glass jar lined inside and out with tinfoil for about two-thirds of its height.FIG. 2.—A Leyden jar is a glass jar lined inside and out with tinfoil for about two-thirds of its height.In throwing the stone into the pool of water, muscular energy of the arm is transferred to the stone, and the latter, upon striking the surface of the pond, imparts a portion of that stored energy to the little waves which are immediately created in the water. In setting up electromagnetic waves for wireless communication the energy imparted to the ether iselectricalenergy, developed by certain interesting instruments explained further on.Let us consider briefly how thewavesare created in a wireless telegraph station. Almost every one has seen and heard the brilliant snapping spark produced by the discharge of a Leyden jar. A Leyden jar in its common form is a glass jar lined inside and out with tinfoil for about two thirds of its height. A brass rod, terminating in a knob, connects below with the inner coating, usually by means of a loose chain. It may be described as a device which is capable of storing electricity in the form of energy and discharging this energy again in actual electricity.This discharge has been the subject of many interesting investigations of direct interest.FIG. 3.—A static machine connected to a Leyden jar.FIG. 3.—A static machine connected to a Leyden jar.The inner and outer coatings are connected to the terminals of a static electric machine (an apparatus for generating electricity), and the machine set in rotation. After the jar has been charged, the electric machine is disconnected and one end of a coil of heavy wire connected to the outside coating, while the other end of the wire is made to approach the knob connected with the inner coating. Before the end of the wire reaches the knob a discharge occurs through the coil, producing a noisy brilliant spark between the wire and the knob. The discharge appears like a single spark, but in reality it is composed of a great many following each other in rapid succession. The jar discharges its energy, first by a tremendous rush of current in one direction, and then another discharge somewhat smaller than the first in the opposite direction. There is a series of these discharges in reverse directions, but each discharge is less and less, until the whole amount of energy is expended. The complete series of discharges takes place in an almost immeasurable fraction of time. It is from this phenomenon that the electrical term "high frequency oscillations," so often heard of in "wireless" parlance, is derived.FIG. 4.—A Leyden jar discharging through a coil of wire produces a brilliant spark and high frequency oscillations are created.FIG. 4.—A Leyden jar discharging through a coil of wire produces a brilliant spark andhigh frequency oscillationsare created.FIG. 5.—Curved line representing an oscillatory discharge of a Leyden jar.FIG. 5.—Curved line representing an oscillatory discharge of a Leyden jar.FIG. 6.—Navy type of Leyden jars. Coated with copper deposited upon the surface of the glass.FIG. 6.—Navy type of Leyden jars. Coated with copper deposited upon the surface of the glass.High frequency oscillations are the "pebbles" which, dropped into the vast pool of ether, everywhere, set up "ripples" calledelectromagnetic waves(identical with the electromagnetic waves of light, butlongerand so beyond the limits of our spectrum and the vision of the eye). The manner in which this is accomplished may be explained by saying that the charge creates a state of strain in the surrounding ether, and then abruptly releases it. Ether possesses a high degree of elasticity, so that when the state of strain is thus suddenly released, it immediately returns to its former state. The sudden motion of the ether results in waves which spread out from their source in enlarging circles.Wireless telegraphy, as it is practiced to-day, is based upon the fact that a system of wires or circuits, through whichhigh frequencyoscillations are surging, becomes a source of electromagnetic waves. Various methods have been devised for making the system more efficient and capable of giving better results with a given amount of power.FIG. 7.—The simplest practical transmitter that it is possible to devise for the purpose of sending messages.FIG. 7.—The simplest practical transmitter that it is possible to devise for the purpose of sending messages.Fig. 7 is a diagram showing the simplest practical transmitter that it is possible to devise for the purpose of sending messages a sufficient distance to be of any value.It would be impractical to use a static electric machine for wireless transmission, and so aninduction coilortransformeris employed. These latter instruments are for the purpose of raising electric currents of a comparatively low voltage to the high potential, where they have the power of generating high frequency oscillations.In the illustration the current from a battery is led into the primary of an induction coil. Theprimaryis simply a coil consisting of a few turns of wire, which induces a high voltage in a second coil consisting of a larger number of turns, and called thesecondary. The terminals of the secondary are led to a spark gap—an arrangement composed of two polished brass balls, separated by a small air space. One of the balls, in turn, is connected to a metal plate buried in the earth, and the other to a network of wires suspended high in the air and insulated from all surrounding objects.As noted above, a Leyden jar consists of two metallic coatings, separated by a wall of glass. The purpose of the coatings is to form aconductorand carry an electric charge. A Leyden jar possesses a characteristic called, in electricity,capacity. Any two conductors separated by an insulating medium possess "capacity" and all the properties of a Leyden jar or condenser.The waves generated by a Leyden jar would be somewhat weak and confined to its own immediate neighborhood, so recourse is had to theaerialandground, in order to increase the area over which the oscillations exert their influence in setting up the electric waves. The aerial system corresponds to one coating of the Leyden jar, and the ground to the other. The insulating medium in between, corresponding to the glass, ordielectric, is the atmosphere.When the key connected to the induction coil is pressed, the battery current flows through the primary and induces a high voltage current in the secondary, which charges the aerial and ground exactly as the static machine charges the two coatings of the Leyden jar. A spark then leaps across the spark gap and the current surges back and forth through the aerial, generating "high frequency oscillations" which, in turn, set up a state of strain in the surrounding ether, and cause the waves to travel out from the system.FIG. 8. If a cross section of the aerial and atmosphere could be made in the same manner that an apple is sliced with a knife and the waves held stationary, they would appear as above.FIG. 8. If a cross section of the aerial and atmosphere could be made in the same manner that an apple is sliced with a knife and the waves held stationary, they would appear as above.These waves follow the contour of the earth, and so may cross mountains and valleys, and travel anywhere. They radiate from the aerial like the ripples from a pebble in a pool of water, in gradually enlarging circles. If a cross section of the aerial and atmosphere could be made in the same manner that an apple can be sliced with a knife, and the waves held stationary long enough to see them, they would appear as in Fig. 8. The curved lines represent the lines of strain induced by the oscillations. Each group of lines represents a wave. It will be noticed as they radiate farther from the aerial that they become larger and spread out.FIG. 9.—Under the same conditions, but when viewed from above, the appearance would be that of a series of concentric circles.FIG. 9.—Under the same conditions, but when viewed from above, the appearance would be that of a series of concentric circles.The electromagnetic waves have the power of exciting oscillations in a conductor on which they impinge. This is made use of for the purpose of receiving the messages. When the waves strike the aerial of a distant station they set up high frequency oscillations, which are usually too weak to make their presence known except with the aid of a sensitive device, called a detector.FIG. 10.—A simple receiving arrangement. The detector rectifies the oscillatory currents passing from the aerial to the ground so that they will flow through the telephone receiver and register as sound.FIG. 10.—A simple receiving arrangement. The detector rectifies the oscillatory currents passing from the aerial to the ground so that they will flow through the telephone receiver and register as sound.The most prominent type of detector in use to-day is a crystal of silicon, iron pyrites, zincite or certain other minerals. The mineral is placed between two contact points, one or both of which are adjustable so that the most sensitive portion of the mineral may be selected. A telephone receiver is connected across the terminals of the detector. When the electromagnetic waves from the transmitting station strike the aerial of the receiving station, they set up therein a series of high frequency oscillations, corresponding to the Morse signals emitted from the transmitter. The oscillations flow back and forth through the aerial and ground, striking themineral detectoron their journey. The high frequency oscillations arealternating currents, because theyreversetheir direction many thousand times per second. Such a current will not pass through the telephone receiver, because the little magnets contained therein exert a choking action on alternating currents of high frequency and effectually block their passage. The mineral detector acts as a valve, allowing the current to pass through in one direction, but not permitting it to return or go in the opposite direction. The result is a series of impulses flowing in one direction only, and therefore called adirectcurrent. Such a current will flow through a telephone receiver and produce a motion of the diaphragm which imparts its motion to the surrounding air, the result being sound waves audible to the ear. By varying the periods during which the key is pressed and the oscillations are being produced, according to a prearranged code, the sounds in the receiver may be made to assume an intelligible meaning.
CHAPTER I. INTRODUCTORY: WIRELESS TRANSMISSION AND RECEPTION. THE ETHER. ELECTRICAL OSCILLATIONS. ELECTROMAGNETIC WAVES.Wireless telegraphy, that marvelous art which has made possible the instantaneous transmission of intelligence between widely distant parts having no apparent physical connection save that of the earth, air, and water, is one of those wonders of science which appeal to the average mind as either incomprehensible or only explainable through the use of highly technical language. Contrary to this general opinion, however, the whole theory and practice of the wireless transmission of messages is capable of the simplest explanation.FIG. 1.—Throw a stone into a pool of water and little waves will radiate from the spot where the stone struck.FIG. 1.—Throw a stone into a pool of water and little waves will radiate from the spot where the stone struck.Throw a stone into a pool of water. A disturbance is immediately created, and little waves will radiate from the spot where the stone struck the water, gradually spreading out into enlarging circles until they reach the shores or die away. By throwing several stones in succession with varying intervals between them it would be possible to so arrange a set of signals that they would convey a meaning to one who is initiated, standing on the opposite side of the pool. The little waves are the vehicle which transmits the intelligence, and the water themediumin which the waves travel.Wireless telegraph instruments are simply a means forcreating and detecting waves in a great pool of ether.Scientists suppose that all space and matter is pervaded with a hypotheticalmediumof extreme tenuity and elasticity, calledluminiferous ether, or simplyether.Although ether is invisible, odorless, and practically weightless, it is not merely the fantastic creation of speculative philosophers, but is as essential to our existence as the air we breathe and the food we eat. By imagining and accepting its reality, it is possible to explain and understand many scientific puzzles. The universe is a vast pool of ether. It is all-pervading. There is no void. It is diffused even among the molecules of which solid bodies are composed. The study of this substance is, perhaps, one of the most fascinating and important duties of the physicist.Ninety million miles away from our earth is a huge flaming body of vapors and gases, called the sun. This seething mass of flame and heat furnishes us more than mere winter and summer and night and day, for we on this earth are not living on our own resources, and the real work of the world so necessary for even bare existence is accomplished by the energy of the sun stored up in coal, in plants and trees and mountain torrents.Light is known to be vibrations of an extremely rapid period—electromagnetic waves, they are called. Heat can be shown to be of the same nature. Traveling at the rate of over 180,000 miles per second, these two great gifts of the sun come streaming continually down to us over the inconceivable distance of almost 100,000,000 miles. Both require a medium for their propagation. The ether supplies it. It is the substance with which the universe is filled. Incidentally it is also the seat of all electrical and magnetic forces.FIG. 2.—A Leyden jar is a glass jar lined inside and out with tinfoil for about two-thirds of its height.FIG. 2.—A Leyden jar is a glass jar lined inside and out with tinfoil for about two-thirds of its height.In throwing the stone into the pool of water, muscular energy of the arm is transferred to the stone, and the latter, upon striking the surface of the pond, imparts a portion of that stored energy to the little waves which are immediately created in the water. In setting up electromagnetic waves for wireless communication the energy imparted to the ether iselectricalenergy, developed by certain interesting instruments explained further on.Let us consider briefly how thewavesare created in a wireless telegraph station. Almost every one has seen and heard the brilliant snapping spark produced by the discharge of a Leyden jar. A Leyden jar in its common form is a glass jar lined inside and out with tinfoil for about two thirds of its height. A brass rod, terminating in a knob, connects below with the inner coating, usually by means of a loose chain. It may be described as a device which is capable of storing electricity in the form of energy and discharging this energy again in actual electricity.This discharge has been the subject of many interesting investigations of direct interest.FIG. 3.—A static machine connected to a Leyden jar.FIG. 3.—A static machine connected to a Leyden jar.The inner and outer coatings are connected to the terminals of a static electric machine (an apparatus for generating electricity), and the machine set in rotation. After the jar has been charged, the electric machine is disconnected and one end of a coil of heavy wire connected to the outside coating, while the other end of the wire is made to approach the knob connected with the inner coating. Before the end of the wire reaches the knob a discharge occurs through the coil, producing a noisy brilliant spark between the wire and the knob. The discharge appears like a single spark, but in reality it is composed of a great many following each other in rapid succession. The jar discharges its energy, first by a tremendous rush of current in one direction, and then another discharge somewhat smaller than the first in the opposite direction. There is a series of these discharges in reverse directions, but each discharge is less and less, until the whole amount of energy is expended. The complete series of discharges takes place in an almost immeasurable fraction of time. It is from this phenomenon that the electrical term "high frequency oscillations," so often heard of in "wireless" parlance, is derived.FIG. 4.—A Leyden jar discharging through a coil of wire produces a brilliant spark and high frequency oscillations are created.FIG. 4.—A Leyden jar discharging through a coil of wire produces a brilliant spark andhigh frequency oscillationsare created.FIG. 5.—Curved line representing an oscillatory discharge of a Leyden jar.FIG. 5.—Curved line representing an oscillatory discharge of a Leyden jar.FIG. 6.—Navy type of Leyden jars. Coated with copper deposited upon the surface of the glass.FIG. 6.—Navy type of Leyden jars. Coated with copper deposited upon the surface of the glass.High frequency oscillations are the "pebbles" which, dropped into the vast pool of ether, everywhere, set up "ripples" calledelectromagnetic waves(identical with the electromagnetic waves of light, butlongerand so beyond the limits of our spectrum and the vision of the eye). The manner in which this is accomplished may be explained by saying that the charge creates a state of strain in the surrounding ether, and then abruptly releases it. Ether possesses a high degree of elasticity, so that when the state of strain is thus suddenly released, it immediately returns to its former state. The sudden motion of the ether results in waves which spread out from their source in enlarging circles.Wireless telegraphy, as it is practiced to-day, is based upon the fact that a system of wires or circuits, through whichhigh frequencyoscillations are surging, becomes a source of electromagnetic waves. Various methods have been devised for making the system more efficient and capable of giving better results with a given amount of power.FIG. 7.—The simplest practical transmitter that it is possible to devise for the purpose of sending messages.FIG. 7.—The simplest practical transmitter that it is possible to devise for the purpose of sending messages.Fig. 7 is a diagram showing the simplest practical transmitter that it is possible to devise for the purpose of sending messages a sufficient distance to be of any value.It would be impractical to use a static electric machine for wireless transmission, and so aninduction coilortransformeris employed. These latter instruments are for the purpose of raising electric currents of a comparatively low voltage to the high potential, where they have the power of generating high frequency oscillations.In the illustration the current from a battery is led into the primary of an induction coil. Theprimaryis simply a coil consisting of a few turns of wire, which induces a high voltage in a second coil consisting of a larger number of turns, and called thesecondary. The terminals of the secondary are led to a spark gap—an arrangement composed of two polished brass balls, separated by a small air space. One of the balls, in turn, is connected to a metal plate buried in the earth, and the other to a network of wires suspended high in the air and insulated from all surrounding objects.As noted above, a Leyden jar consists of two metallic coatings, separated by a wall of glass. The purpose of the coatings is to form aconductorand carry an electric charge. A Leyden jar possesses a characteristic called, in electricity,capacity. Any two conductors separated by an insulating medium possess "capacity" and all the properties of a Leyden jar or condenser.The waves generated by a Leyden jar would be somewhat weak and confined to its own immediate neighborhood, so recourse is had to theaerialandground, in order to increase the area over which the oscillations exert their influence in setting up the electric waves. The aerial system corresponds to one coating of the Leyden jar, and the ground to the other. The insulating medium in between, corresponding to the glass, ordielectric, is the atmosphere.When the key connected to the induction coil is pressed, the battery current flows through the primary and induces a high voltage current in the secondary, which charges the aerial and ground exactly as the static machine charges the two coatings of the Leyden jar. A spark then leaps across the spark gap and the current surges back and forth through the aerial, generating "high frequency oscillations" which, in turn, set up a state of strain in the surrounding ether, and cause the waves to travel out from the system.FIG. 8. If a cross section of the aerial and atmosphere could be made in the same manner that an apple is sliced with a knife and the waves held stationary, they would appear as above.FIG. 8. If a cross section of the aerial and atmosphere could be made in the same manner that an apple is sliced with a knife and the waves held stationary, they would appear as above.These waves follow the contour of the earth, and so may cross mountains and valleys, and travel anywhere. They radiate from the aerial like the ripples from a pebble in a pool of water, in gradually enlarging circles. If a cross section of the aerial and atmosphere could be made in the same manner that an apple can be sliced with a knife, and the waves held stationary long enough to see them, they would appear as in Fig. 8. The curved lines represent the lines of strain induced by the oscillations. Each group of lines represents a wave. It will be noticed as they radiate farther from the aerial that they become larger and spread out.FIG. 9.—Under the same conditions, but when viewed from above, the appearance would be that of a series of concentric circles.FIG. 9.—Under the same conditions, but when viewed from above, the appearance would be that of a series of concentric circles.The electromagnetic waves have the power of exciting oscillations in a conductor on which they impinge. This is made use of for the purpose of receiving the messages. When the waves strike the aerial of a distant station they set up high frequency oscillations, which are usually too weak to make their presence known except with the aid of a sensitive device, called a detector.FIG. 10.—A simple receiving arrangement. The detector rectifies the oscillatory currents passing from the aerial to the ground so that they will flow through the telephone receiver and register as sound.FIG. 10.—A simple receiving arrangement. The detector rectifies the oscillatory currents passing from the aerial to the ground so that they will flow through the telephone receiver and register as sound.The most prominent type of detector in use to-day is a crystal of silicon, iron pyrites, zincite or certain other minerals. The mineral is placed between two contact points, one or both of which are adjustable so that the most sensitive portion of the mineral may be selected. A telephone receiver is connected across the terminals of the detector. When the electromagnetic waves from the transmitting station strike the aerial of the receiving station, they set up therein a series of high frequency oscillations, corresponding to the Morse signals emitted from the transmitter. The oscillations flow back and forth through the aerial and ground, striking themineral detectoron their journey. The high frequency oscillations arealternating currents, because theyreversetheir direction many thousand times per second. Such a current will not pass through the telephone receiver, because the little magnets contained therein exert a choking action on alternating currents of high frequency and effectually block their passage. The mineral detector acts as a valve, allowing the current to pass through in one direction, but not permitting it to return or go in the opposite direction. The result is a series of impulses flowing in one direction only, and therefore called adirectcurrent. Such a current will flow through a telephone receiver and produce a motion of the diaphragm which imparts its motion to the surrounding air, the result being sound waves audible to the ear. By varying the periods during which the key is pressed and the oscillations are being produced, according to a prearranged code, the sounds in the receiver may be made to assume an intelligible meaning.
Wireless telegraphy, that marvelous art which has made possible the instantaneous transmission of intelligence between widely distant parts having no apparent physical connection save that of the earth, air, and water, is one of those wonders of science which appeal to the average mind as either incomprehensible or only explainable through the use of highly technical language. Contrary to this general opinion, however, the whole theory and practice of the wireless transmission of messages is capable of the simplest explanation.
FIG. 1.—Throw a stone into a pool of water and little waves will radiate from the spot where the stone struck.FIG. 1.—Throw a stone into a pool of water and little waves will radiate from the spot where the stone struck.
FIG. 1.—Throw a stone into a pool of water and little waves will radiate from the spot where the stone struck.
Throw a stone into a pool of water. A disturbance is immediately created, and little waves will radiate from the spot where the stone struck the water, gradually spreading out into enlarging circles until they reach the shores or die away. By throwing several stones in succession with varying intervals between them it would be possible to so arrange a set of signals that they would convey a meaning to one who is initiated, standing on the opposite side of the pool. The little waves are the vehicle which transmits the intelligence, and the water themediumin which the waves travel.
Wireless telegraph instruments are simply a means forcreating and detecting waves in a great pool of ether.
Scientists suppose that all space and matter is pervaded with a hypotheticalmediumof extreme tenuity and elasticity, calledluminiferous ether, or simplyether.
Although ether is invisible, odorless, and practically weightless, it is not merely the fantastic creation of speculative philosophers, but is as essential to our existence as the air we breathe and the food we eat. By imagining and accepting its reality, it is possible to explain and understand many scientific puzzles. The universe is a vast pool of ether. It is all-pervading. There is no void. It is diffused even among the molecules of which solid bodies are composed. The study of this substance is, perhaps, one of the most fascinating and important duties of the physicist.
Ninety million miles away from our earth is a huge flaming body of vapors and gases, called the sun. This seething mass of flame and heat furnishes us more than mere winter and summer and night and day, for we on this earth are not living on our own resources, and the real work of the world so necessary for even bare existence is accomplished by the energy of the sun stored up in coal, in plants and trees and mountain torrents.
Light is known to be vibrations of an extremely rapid period—electromagnetic waves, they are called. Heat can be shown to be of the same nature. Traveling at the rate of over 180,000 miles per second, these two great gifts of the sun come streaming continually down to us over the inconceivable distance of almost 100,000,000 miles. Both require a medium for their propagation. The ether supplies it. It is the substance with which the universe is filled. Incidentally it is also the seat of all electrical and magnetic forces.
FIG. 2.—A Leyden jar is a glass jar lined inside and out with tinfoil for about two-thirds of its height.FIG. 2.—A Leyden jar is a glass jar lined inside and out with tinfoil for about two-thirds of its height.
FIG. 2.—A Leyden jar is a glass jar lined inside and out with tinfoil for about two-thirds of its height.
In throwing the stone into the pool of water, muscular energy of the arm is transferred to the stone, and the latter, upon striking the surface of the pond, imparts a portion of that stored energy to the little waves which are immediately created in the water. In setting up electromagnetic waves for wireless communication the energy imparted to the ether iselectricalenergy, developed by certain interesting instruments explained further on.
Let us consider briefly how thewavesare created in a wireless telegraph station. Almost every one has seen and heard the brilliant snapping spark produced by the discharge of a Leyden jar. A Leyden jar in its common form is a glass jar lined inside and out with tinfoil for about two thirds of its height. A brass rod, terminating in a knob, connects below with the inner coating, usually by means of a loose chain. It may be described as a device which is capable of storing electricity in the form of energy and discharging this energy again in actual electricity.
This discharge has been the subject of many interesting investigations of direct interest.
FIG. 3.—A static machine connected to a Leyden jar.FIG. 3.—A static machine connected to a Leyden jar.
FIG. 3.—A static machine connected to a Leyden jar.
The inner and outer coatings are connected to the terminals of a static electric machine (an apparatus for generating electricity), and the machine set in rotation. After the jar has been charged, the electric machine is disconnected and one end of a coil of heavy wire connected to the outside coating, while the other end of the wire is made to approach the knob connected with the inner coating. Before the end of the wire reaches the knob a discharge occurs through the coil, producing a noisy brilliant spark between the wire and the knob. The discharge appears like a single spark, but in reality it is composed of a great many following each other in rapid succession. The jar discharges its energy, first by a tremendous rush of current in one direction, and then another discharge somewhat smaller than the first in the opposite direction. There is a series of these discharges in reverse directions, but each discharge is less and less, until the whole amount of energy is expended. The complete series of discharges takes place in an almost immeasurable fraction of time. It is from this phenomenon that the electrical term "high frequency oscillations," so often heard of in "wireless" parlance, is derived.
FIG. 4.—A Leyden jar discharging through a coil of wire produces a brilliant spark and high frequency oscillations are created.FIG. 4.—A Leyden jar discharging through a coil of wire produces a brilliant spark andhigh frequency oscillationsare created.
FIG. 4.—A Leyden jar discharging through a coil of wire produces a brilliant spark andhigh frequency oscillationsare created.
FIG. 5.—Curved line representing an oscillatory discharge of a Leyden jar.FIG. 5.—Curved line representing an oscillatory discharge of a Leyden jar.
FIG. 5.—Curved line representing an oscillatory discharge of a Leyden jar.
FIG. 6.—Navy type of Leyden jars. Coated with copper deposited upon the surface of the glass.FIG. 6.—Navy type of Leyden jars. Coated with copper deposited upon the surface of the glass.
FIG. 6.—Navy type of Leyden jars. Coated with copper deposited upon the surface of the glass.
High frequency oscillations are the "pebbles" which, dropped into the vast pool of ether, everywhere, set up "ripples" calledelectromagnetic waves(identical with the electromagnetic waves of light, butlongerand so beyond the limits of our spectrum and the vision of the eye). The manner in which this is accomplished may be explained by saying that the charge creates a state of strain in the surrounding ether, and then abruptly releases it. Ether possesses a high degree of elasticity, so that when the state of strain is thus suddenly released, it immediately returns to its former state. The sudden motion of the ether results in waves which spread out from their source in enlarging circles.
Wireless telegraphy, as it is practiced to-day, is based upon the fact that a system of wires or circuits, through whichhigh frequencyoscillations are surging, becomes a source of electromagnetic waves. Various methods have been devised for making the system more efficient and capable of giving better results with a given amount of power.
FIG. 7.—The simplest practical transmitter that it is possible to devise for the purpose of sending messages.FIG. 7.—The simplest practical transmitter that it is possible to devise for the purpose of sending messages.
FIG. 7.—The simplest practical transmitter that it is possible to devise for the purpose of sending messages.
Fig. 7 is a diagram showing the simplest practical transmitter that it is possible to devise for the purpose of sending messages a sufficient distance to be of any value.
It would be impractical to use a static electric machine for wireless transmission, and so aninduction coilortransformeris employed. These latter instruments are for the purpose of raising electric currents of a comparatively low voltage to the high potential, where they have the power of generating high frequency oscillations.
In the illustration the current from a battery is led into the primary of an induction coil. Theprimaryis simply a coil consisting of a few turns of wire, which induces a high voltage in a second coil consisting of a larger number of turns, and called thesecondary. The terminals of the secondary are led to a spark gap—an arrangement composed of two polished brass balls, separated by a small air space. One of the balls, in turn, is connected to a metal plate buried in the earth, and the other to a network of wires suspended high in the air and insulated from all surrounding objects.
As noted above, a Leyden jar consists of two metallic coatings, separated by a wall of glass. The purpose of the coatings is to form aconductorand carry an electric charge. A Leyden jar possesses a characteristic called, in electricity,capacity. Any two conductors separated by an insulating medium possess "capacity" and all the properties of a Leyden jar or condenser.
The waves generated by a Leyden jar would be somewhat weak and confined to its own immediate neighborhood, so recourse is had to theaerialandground, in order to increase the area over which the oscillations exert their influence in setting up the electric waves. The aerial system corresponds to one coating of the Leyden jar, and the ground to the other. The insulating medium in between, corresponding to the glass, ordielectric, is the atmosphere.
When the key connected to the induction coil is pressed, the battery current flows through the primary and induces a high voltage current in the secondary, which charges the aerial and ground exactly as the static machine charges the two coatings of the Leyden jar. A spark then leaps across the spark gap and the current surges back and forth through the aerial, generating "high frequency oscillations" which, in turn, set up a state of strain in the surrounding ether, and cause the waves to travel out from the system.
FIG. 8. If a cross section of the aerial and atmosphere could be made in the same manner that an apple is sliced with a knife and the waves held stationary, they would appear as above.FIG. 8. If a cross section of the aerial and atmosphere could be made in the same manner that an apple is sliced with a knife and the waves held stationary, they would appear as above.
FIG. 8. If a cross section of the aerial and atmosphere could be made in the same manner that an apple is sliced with a knife and the waves held stationary, they would appear as above.
These waves follow the contour of the earth, and so may cross mountains and valleys, and travel anywhere. They radiate from the aerial like the ripples from a pebble in a pool of water, in gradually enlarging circles. If a cross section of the aerial and atmosphere could be made in the same manner that an apple can be sliced with a knife, and the waves held stationary long enough to see them, they would appear as in Fig. 8. The curved lines represent the lines of strain induced by the oscillations. Each group of lines represents a wave. It will be noticed as they radiate farther from the aerial that they become larger and spread out.
FIG. 9.—Under the same conditions, but when viewed from above, the appearance would be that of a series of concentric circles.FIG. 9.—Under the same conditions, but when viewed from above, the appearance would be that of a series of concentric circles.
FIG. 9.—Under the same conditions, but when viewed from above, the appearance would be that of a series of concentric circles.
The electromagnetic waves have the power of exciting oscillations in a conductor on which they impinge. This is made use of for the purpose of receiving the messages. When the waves strike the aerial of a distant station they set up high frequency oscillations, which are usually too weak to make their presence known except with the aid of a sensitive device, called a detector.
FIG. 10.—A simple receiving arrangement. The detector rectifies the oscillatory currents passing from the aerial to the ground so that they will flow through the telephone receiver and register as sound.FIG. 10.—A simple receiving arrangement. The detector rectifies the oscillatory currents passing from the aerial to the ground so that they will flow through the telephone receiver and register as sound.
FIG. 10.—A simple receiving arrangement. The detector rectifies the oscillatory currents passing from the aerial to the ground so that they will flow through the telephone receiver and register as sound.
The most prominent type of detector in use to-day is a crystal of silicon, iron pyrites, zincite or certain other minerals. The mineral is placed between two contact points, one or both of which are adjustable so that the most sensitive portion of the mineral may be selected. A telephone receiver is connected across the terminals of the detector. When the electromagnetic waves from the transmitting station strike the aerial of the receiving station, they set up therein a series of high frequency oscillations, corresponding to the Morse signals emitted from the transmitter. The oscillations flow back and forth through the aerial and ground, striking themineral detectoron their journey. The high frequency oscillations arealternating currents, because theyreversetheir direction many thousand times per second. Such a current will not pass through the telephone receiver, because the little magnets contained therein exert a choking action on alternating currents of high frequency and effectually block their passage. The mineral detector acts as a valve, allowing the current to pass through in one direction, but not permitting it to return or go in the opposite direction. The result is a series of impulses flowing in one direction only, and therefore called adirectcurrent. Such a current will flow through a telephone receiver and produce a motion of the diaphragm which imparts its motion to the surrounding air, the result being sound waves audible to the ear. By varying the periods during which the key is pressed and the oscillations are being produced, according to a prearranged code, the sounds in the receiver may be made to assume an intelligible meaning.