  The camera sees things invisible to the human eye. Its most effective work is done with beams which are beyond human perception. The photographer uses the Actinic rays. Ordinary light is composed of the seven primary colors, of which the lowest in the scale is the red, and the highest to violet. Those below the red are called the Infra-red, and they are the Hertzian waves, or those used in wireless telegraphy. Those above the violet are called Ultra-violet, and these are employed for X-ray work. The former are produced by the high tension electric apparatus, which we have described in the chapter relating to wireless telegraphy; and the latter, called also the Roentgen rays, are generated by the Crookes' Tube. This is a tube from which all the atmosphere has been extracted so that it is a practical vacuum. Within this are placed electrodes so as to divert the action of the electrical discharge in a particular direction, and this light, when discharged, is of such a peculiar character that its discovery made a sensation in the scientific world The reason for this great wonder was not in the fact that it projected a light, but because of its character. Ordinary light, as we see it with the eye, is capable of being reflected, as when we look into a mirror at an angle. The X-ray will not reflect, but instead, pass directly through the glass. Then, ordinary light is capable of refraction. This is shown by a ray of light bending as it passes through a glass of water, which is noticed when the light is at an angle to the surface. The X-ray will pass through the water without being changed from a straight line. The foregoing being the case, it was but a simple step to conclude that if it were possible to find a means whereby the human eye could see within the ultra-violet beam, it would be possible to see through opaque substances. From the discovery so important and far reaching it was not long until it was found that if the ultra-violet rays, thus propagated, were transmitted through certain substances, their rates of vibration would be brought down to the speeds which send forth the visible rays, and now the eye is able to see, in a measure at least, what the actinic rays show. This discovery was but the forerunner of a still more important development, namely, the discovery of radium. The actual finding of the metal Radio-activity is a word used to express that quality in metals or other material by means of which obscure rays are emitted, that have the capacity of discharging electrified bodies, and the power to ionize gases, as well as to actually affect photograph plates. Certain metals had this property to a remarkable degree, particularly uranium, thorium, polonium, actinium, and others, and in 1898 the Curies, husband and wife, French chemists, isolated an element, very ductile in its character, which was a white metal, and had a most brilliant luster. Pitchblende, the base metal from which this was extracted, was discovered to be highly radio-active, and on making tests of the product taken from it, they were surprised to find that it emitted a form of energy that far exceeded in calculations any computations made on the basis of radio-activity in the metals hitherto examined. But this was not the most remarkable part of the developments. The energy, whatever it was, had the power to change many other substances if brought into close proximity. It darkens the color of diamonds, quartz, mica, and glass. It changes some of the latter in color, some kinds being Radium has the capacity to redden the skin, and affect the flesh of persons, even at some considerable distance, and it is a most powerful germicide, destroying bacteria, and has been found also to produce some remarkable cures in diseases of a cancerous nature. The remarkable similarity of the rays propagated by this substance, with the X-rays, lead many to believe that they are electrical in their character, and the whole scientific world is now striving to use this substance, as well as the more familiar light waves of the Roentgen tube, in the healing of diseases. It is not at all remarkable that this use of it should first be considered, as it has been the history of the electrical developments, from the earliest times, that each successive stage should find advocates who would urge its virtues to heal the sick. It was so when the dynamo was invented, when the high tension current was produced; and electrical therapeutics became a leading theme when transmission by induction became recognized as a scientific fact. It is not many years since the X-rays were discovered, This was particularly true in the case of radium, but for some reason, after the first tests, all experimenters were thwarted in their theories, because the science, like all others, required infinite patience and experience. It was discovered, in the case of the X-ray, that it must be used in a modified form, and accordingly, various modifications of the waves were introduced, called the m and the n rays, as well as many others, each having some peculiar qualification. In time, no doubt, the investigators will find the right quality for each disease, and learn how to apply it. Thus, electricity, that most alluring thing which, in itself, cannot be seen, and is of such a character that it cannot even be defined in terms which will suit the exact scientific mind, is daily bringing new wonders for our investigation and use. It is, indeed, a study which is so broad that it has no limitations, and a field which never will be exhausted. THE END
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| Acid. | Accumulator material is sulphuric acid, diluted with water. |
| Active Material. | That part of the material in accumulator plates which is acted upon by the electric current. |
| Accumulator. | A cell, generally known as a storage battery, which while it initially receives a charge of electricity, is nevertheless, of such a character, owing to the active material of which it is made, that it accumulates, or, as it were, generates electricity. |
| Aerial Wire, or Conductor. | The wire which, in wireless telegraphy, is carried up into the air to connect the antennÆ with the receiving and sending apparatus. |
| Alarm, Burglar. | A circulating system in a building, connected up with a bell or other signaling means. |
| Alloy. | A mixture of two or more metals; as copper and zinc to make brass; nickel and zinc to form German silver. |
| Alternating Current. | A current which goes back and forth in opposite directions, unlike a direct current which flows continuously in one direction over a wire. |
| Alternation. | The term applied to a change in the direction of an alternating current, the frequency of the alternations ranging up to 20,000 or more vibrations per second. |
| Amber. | A resin, yellow in color, which when rubbed with a cloth, becomes excited and gives forth negative |
| Ammeter. | An instrument for measuring the quantity or flow of electricity. |
| Ampere. | The unit of current; the term in which strength of the current is measured. An ampere is an electromotive force of one volt through a resistance of one ohm. |
| Annunciator. | A device which indicates or signals a call given from some distant point. |
| Anode. | The positive terminal in a conducting circuit, like the terminal of the carbon plate in a battery. It is a plate in an electroplating bath from which the current goes over to the cathode or negative plate or terminal. |
| Arc. | A term employed to designate the gap, or the current which flows across between the conductors, like the space between the two carbons of an arc lamp, which gives the light. |
| Armature. | A body of iron, or other suitable metal, which is in the magnetic field of a magnet. |
| Armature Bar. | The piece which holds the armature. Also one of a series of bars which form the conductors in armature windings. |
| Armature Coil. | The winding around an armature, or around the core of an armature. |
| Armature Core. | The part in a dynamo or motor which revolves, and on which the wire coils are wound. |
| Astatic (Galvanometer). | That which has no magnetic action to direct or divert anything exterior to it. |
| Atom. | The ultimate particle of an elementary substance. |
| Attraction. | That property of matter which causes particles to adhere, or cohere, to each other. It is known |
| Automatic Cut-out. | A device which acts through the operation of the mechanism with which it is connected. It is usually applied to a device which cuts out a current when it overcharges or overloads the wire. |
| Bath. | In electroplating, the vessel or tank which holds the electroplating solution. |
| Battery. | A combination of two or more cells. |
| Battery, Dry. | A primary battery in which the electrolyte is made in a solid form. |
| Battery, Galvanic. | A battery which is better known by the name of the Voltaic Pile, made up of zinc and copper plates which alternate, and with a layer of acidulated paper between each pair of plates. |
| Battery, Storage. | A battery which accumulates electricity generated by a primary battery or a generator. |
| Brush. | A term applied to the conducting medium that bears against the cylindrical surface of a commutator. |
| Buzzer. | An electric call produced by a rapidly moving armature of an electro-magnet. |
| Cable. | A number of wires or conductors assembled in one strand. |
| Candle-power. | The amount of light given by the legal-standard candle. This standard is a sperm candle, which burns two grains a minute. |
| Capacity. | The carrying power of a wire or circuit, without heating. When heated there is an overload, or the capacity of the wire is overtaxed. |
| Capacity, Storage. | The quantity of electricity in a secondary battery when fully charged, usually reckoned in ampere |
| Carbon. | A material, like coke, ground or crushed, and formed into sticks or plates by molding or compression. It requires a high heat to melt or burn, and is used as electrodes for arc lamps and for battery elements. It has poor conductivity, and for arc lamps is coated with copper to increase its conductivity. |
| Cell, Electrolytic. | A vessel containing an electrolyte for electroplating purposes. |
| Charge. | The quantity of electricity on the surface of a body or conductor. |
| Chemical Change. | When a current passes through electrodes in a solution, a change takes place which is chemical in its character. Adding sulphuric acid to water produces heat. If electrodes of opposite polarity are placed in such an acid solution, a chemical change is produced, which is transformed into electricity. |
| Choking Coil. | An instrument in a circuit which by a form of resistance regulates the flow of the current, or returns part of it to the source of its generation. |
| Counter-electromotive Force. | Cells which are inserted in opposition to a battery to reduce high voltage. |
| Circuit, Astatic. | A circuit in an instrument so wound that the earth's magnetism will not affect it. |
| Circuit Breaker. | Any instrument in a circuit which cuts out or interrupts the flow of a current. |
| Circuit, External. | A current flows through a wire or conductor, and also along the air outside of the conductor, the latter being the external circuit. |
| Circuit Indicator. | An instrument, like a galvanometer, that shows the direction in which a current is flowing through a |
| Circuit, Return. | Usually the ground return, or the negative wire from a battery. |
| Circuit, Short. | Any connection between the mains or parallel lines of a circuit which does not go through the apparatus for which the circuit is intended. |
| Coherer. | A tube, or other structure, containing normally high resistance particles which form a path or bridge between the opposite terminals of a circuit. |
| Coil. | A wire, usually insulated, wound around a spool. |
| Coil, Induction. | One of a pair of coils designed to change the voltage of a current of electricity, from a higher to a lower, or from a lower to a higher electro-motive force. |
| Coil, Resistance. | A coil so wound that it will offer a resistance to a steady current, or reduce the flow of electricity. |
| Commutator. | A cylinder on the end of the armature of a dynamo or motor and provided with a pair of contact plates for each particular coil in the armature, in order to change the direction of the current. |
| Compass. | An apparatus which indicates the direction or flow of the earth's magnetism. |
| Condenser. | A device for storing up electro-static charges. |
| Conductance. | That quality of a conductor to carry a current of electricity, dependent on its shape for the best results. |
| Conduction. | The transmission of a current through a rod, wire or conductor. |
| Conductivity. | That quality which has reference to the capacity to conduct a current. |
| Conductor. | Any body, such as a bar, rod, wire, or machine, which will carry a current. |
| Connector. | A binding post, clamp, screw, or other means to hold |
| Contact. | To unite any parts in an electric circuit. |
| Controller. | The handle of a switchboard, or other contact making and breaking means in a circuit. |
| Converter. | An induction coil in an alternating circuit for changing potential difference, such as high alternating voltage into low direct current voltage. |
| Convolution. | To wind like a clock spring. |
| Core. | The inner portion of an electro-magnet. The inside part of an armature wound with wire. |
| Core, Laminated. | When the core is built up of a number of separate pieces of the same material, but not insulated from each other. |
| Coulomb. | The unit of electrical quantity. It is the quantity passed by a current of one ampere intensity in one second of time. |
| Couple, Electric. | Two or more electrodes in a liquid to produce an electric force. |
| Current, Alternating. | A natural current produced by the action of electro-magnets. It is a succession of short impulses in opposite directions. |
| Current, Constant. | A current which is uniformly maintained in a steady stream. |
| Current, Induced. | A current produced by electro-dynamic induction. |
| Current Meter. | An apparatus for indicating the strength of a current. An ammeter. |
| Current, Oscillating. | A current which periodically alternates. |
| Current, Periodic. | A periodically varying current strength. |
| Current, Undulating. | A current which has a constant direction, but has a |
| Decomposition. | The separation of a liquid, such as an electrolyte, into its prime elements, either electrically or otherwise. |
| Deflection. | The change of movement of a magnetic needle out of its regular direction of movement. |
| Demagnetization. | When a current passes through a coil wound on an iron core, the core becomes magnetized. When the current ceases the core is no longer a magnet. It is then said to be demagnetized. It also has reference to the process for making a watch non-magnetic so that it will not be affected when in a magnetic field. |
| Density. | The quantity of an electric charge in a conductor or substance. |
| Depolarization. | The removal of magnetism from a permanent magnet, or a horse-shoe magnet, for instance. It is generally accomplished by applying heat. |
| Deposition, Electrolysis. | The act of carrying metal from one pole of a cell to another pole, as in electroplating. |
| Detector. | Mechanism for indicating the presence of a current in a circuit. |
| Diaphragm. | A plate in a telephone, which, in the receiver, is in the magnetic field of a magnet, and in a transmitter carries the light contact points. |
| Dielectric. | A non-conductor for an electric current, but through which electro-static induction will take place. For example: glass and rubber are dielectrics. |
| Discharge. | The current flowing from an accumulator. |
| Disintegration. | The breaking up of the plate or active material. |
| Disruptive. | A static discharge passing through a dielectric. |
| Duplex Wire. | A pair of wires usually twisted together and insulated from each other to form the conducting |
| Dynamic Electricity. | The term applied to a current flowing through a wire. |
| Dynamo. | An apparatus, consisting of core and field magnets, which, when the core is turned, will develop a current of electricity. |
| Earth Returns. | Instead of using two wires to carry a circuit, the earth is used for what is called the return circuit. |
| Efficiency. | The total electrical energy produced, in which that wasted, as well as that used, is calculated. |
| Elasticity. | That property of any matter which, after a stress, will cause the substance to return to its original form or condition. Electricity has elasticity, which is utilized in condensers, as an instance. |
| Electricity, Atmospheric. | Lightning, and, in short, any current or electrical impulse, like wireless telegraphic waves, is called atmospheric. |
| Electricity, Voltaic. | Electricity with a low potentiality and large current density. |
| Electrification. | The process of imparting a charge of electricity to any body. |
| Electro-chemistry. | The study of which treats of electric and chemical forces, such as electric plating, electric fusing, electrolysis, and the like. |
| Electrode. | The terminals of a battery, or of any circuit; as, for instance, an arc light. |
| Electrolyte. | Any material which is capable of being decomposed by an electric current. |
| Electro-magnetism. | Magnetism which is created by an electric current. |
| Electrometer. | An instrument for measuring static electricity, differing from a galvanometer, which measures a current in a wire that acts on the magnetic needle |
| Electro-motive Force. | (E. M. F.) Voltage, which is the measure or unit of e. m. f. |
| Electroscope. | A device for indicating not only the presence of electricity, but whether it is positive or negative. |
| Electro-static Accumulator. | Surfaces separated by a dielectric for opposite charging of the surface. |
| Element. | In electricity a form of matter, as, for instance, gold, or silver, that has no other matter or compound. Original elements cannot be separated, because they are not made up of two or more elements, like brass, for instance. |
| Excessive Charge. | A storage battery charged at too high a rate. |
| Excessive Discharge. | A storage battery discharged at too high a rate. |
| Excessive Overcharge. | Charging for too long a time. |
| Exciter. | A generator, either a dynamo or a battery, for exciting the field of a dynamo. |
| Exhaustive Discharge. | An excessive over-discharge of an accumulator. |
| F. | The sign used to indicate the heat term Fahrenheit. |
| Fall of Voltage. | The difference between the initial and the final voltage in a current. |
| Field. | The space or region near a magnet or charged wire. Also the electro-magnets in a dynamo or motor. |
| Flow. | The volume of a current going through a conductor. |
| Force, Electro-magnetic. | The pull developed by an electro-magnet. |
| Frictional Electricity. | A current produced by rubbing dissimilar substances together. |
| Full Load. | The greatest load a battery, accumulator or dynamo |
| Galvanic. | Pertaining to the electro-chemical relations of metals toward each other. |
| Galvanizing. | The art of coating one metal with another, such, for instance, as immersing iron in molten zinc. |
| Galvanometry. | An instrument having a permanently magnetized needle, which is influenced by a coil or a wire in close proximity to it. |
| Galvanoscope. | An instrument, like a galvanometer, which determines whether or not a current is present in a tested wire. |
| Generator. | A term used to generally indicate any device which originates a current. |
| German Silver. | An alloy of copper, nickel and zinc. |
| Graphite. | One form of carbon. It is made artificially by the electric current. |
| Grid. | The metallic frame of a plate used to hold the active material of an accumulator. |
| Gravity. | The attraction of mass for mass. Weight. The accelerating tendency of material to move toward the earth. |
| Gutta Percha. | Caoutchouc, which has been treated with sulphur, to harden it. It is produced from the sap of tropical trees, and is a good insulator. |
| Harmonic Receiver. | A vibrating reed acted on by an electro-magnet, when tuned to its pitch. |
| High E. M. F. | A term to indicate currents which have a high voltage, and usually low amperage. |
| Igniter. | Mechanism composed of a battery, induction coil and a vibrator, for making a jump spark, to ignite gas, powder, etc. |
| I. H. P. | Abbreviation, which means Indicated Horse Power. |
| Impulse. | A sudden motion of one body acting against another. |
| Incandescence, Electric. | A conductor heated up by a current so it will glow. |
| Induced Current. | A current of electricity which sets up lines of force at right angles to the body of the wire through which the current is transmitted. |
| Induction, Magnetic. | A body within a magnetic field which is excited by the magnetism. |
| Installation. | Everything belonging to an equipment of a building, or a circuiting system to do a certain thing. |
| Insulation. | A material or substance which resists the passage of a current placed around a conductor. |
| Intensity. | The strength of a magnetic field, or of a current flowing over a wire. |
| Internal Resistance. | The current strength of electricity of a wire to resist the passage. |
| Interrupter. | A device in a wire or circuit for checking a current. It also refers to the vibrator of an induction coil. |
| Joint. | The place where two or more conductors are united. |
| Joint Resistance. | The combined resistance offered by two or more substances or conductors. |
| Jump Spark. | A spark, disruptive in its character, between two conducting points. |
| Initial Charge. | The charge required to start a battery. |
| Kathode, or Cathode. | The negative plate or side of a battery. The plate on which the electro deposit is made. |
| Key. | The arm of a telegraph sounder. A bar with a finger piece, which is hinged and so arranged that it will make and break contacts in an electric circuit. |
| Keyboard. | A switch-board; a board on which is mounted a number |
| Kilowatt. | A unit, representing 1,000 watts. An electric current measure, usually expressed thus: K.W. |
| Kilowatt Hour. | The computation of work equal to the exertion of one kilowatt in one hour. |
| Knife Switch. | A bar of a blade-like form, adapted to move down between two fingers, and thus establish metallic connections. |
| Laminated. | Made up of thin plates of the same material, laid together, but not insulated from each other. |
| Lamp Arc. | A voltaic arc lamp, using carbon electrodes, with mechanism for feeding the electrodes regularly. |
| Lamp, Incandescent. | A lamp with a filament heated up to a glow by the action of an electric current. The filament is within a vacuum in a glass globe. |
| Leak. | Loss of electrical energy through a fault in wiring, or in using bare wires. |
| Load. | The ampere current delivered by a dynamo under certain conditions. |
| Low Frequency. | A current in which the vibrations are of few alternations per second. |
| Magnet. | A metallic substance which has power to attract iron and steel. |
| Magnet Bar. | A straight piece of metal. |
| Magnet Coil. | A coil of wire, insulated, surrounding a core of iron, to receive a current of electricity. |
| Magnet Core. | A bar of iron adapted to receive a winding of wire. |
| Magnet, Field. | A magnet in a dynamo. A motor to produce electric energy. |
| Magnet, Permanent. | A short steel form, to hold magnetism for a long time. |
| Magnetic Adherence. | The adherence of particles to the poles of a magnet. |
| Magnetic Attraction and Repulsion. | That quality of a metal which draws metals. Also the pulling action of unlike poles for each other, and pushing away of like poles when brought together. |
| Magnetic Force. | The action exercised by a magnet of attracting or repelling. |
| Magnetic Pole. | The earth has North and South magnetic poles. The south pole of a magnetic needle is attracted so it points to the north magnetic pole; and the north pole of the needle is attracted to point to the south magnetic pole. |
| Magneto-generator. | A permanent magnet and a revolving armature for generating a current. |
| Maximum Voltage. | The final voltage after charging. |
| Molecule. | Invisible particles made up of two or more atoms of different matter. An atom is a particle of one substance only. |
| Morse Sounder. | An electric instrument designed to make a clicking sound, when the armature is drawn down by a magnet. |
| Motor-dynamo. | A motor and a dynamo having their armatures connected together, whereby the motor is driven by the dynamo, so as to change the current into a different voltage and amperage. |
| Motor-transformer. | A motor which delivers the current like a generator. |
| Needle. | A bar magnet horizontally poised on a vertical pivot point, like the needle of a mariner's compass. |
| Negative Electricity. | Amber, when rubbed, produces negative electricity. |
| Negative Element. | That plate in the solution of a battery cell which is not disintegrated. |
| Normal. | The usual, or ordinary. The average. In a current the regular force required to do the work. |
| North Pole, Electric. | The term applied to the force located near the north pole of the globe, to which a permanent magnet will point if allowed to swing freely. |
| O. | Abbreviation for Ohm. |
| Ohm. | The unit of resistance. Equal to the resistance of a column of mercury one square millimeter in cross section, and 106.24 centimeters in length. |
| Ohm's Law. | It is expressed as follows:
|
| Overload. | In a motor an excess of mechanical work which causes the armature to turn too slowly and produces heat. |
| Phase. | One complete oscillation. The special form of a wave at any instant, or at any interval of time. |
| Plate, Condenser. | In a static machine it is usually a plate of glass and revoluble. |
| Plate, Negative. | The plate in a battery, such as carbon, copper or platinum, which is not attacked by the solution. |
| Plating, Electro-. | The method of coating one metal with another by electrolysis. |
| Polarity. | The peculiarity, in a body, of arranging itself with reference to magnetic influence. |
| Parallel. | When a number of cells are coupled so that their |
| Polarization. | When the cell is deprived of its electro-motive force, or any part of it, polarization is the result. It is usually caused by coating of the plates. |
| Porosity. | Having small interstices or holes. |
| Positive Current. | One which deflects a needle to the left. |
| Positive Electricity. | Any current flowing from the active element, such as zinc, in a battery. The negative electricity flows from the carbon to the zinc. |
| Potential, Electric. | The power whi ch performs work in a circuit. |
| Potential Energy. | That form of force, which, when liberated, does or performs work. |
| Power Unit. | The volt-amperes or watt. |
| Primary. | The induction coil in induction machines, or in a transformer. |
| Push Button. | A thumb piece which serves as a switch to close a circuit while being pressed inwardly. |
| Quantity. | Such arrangement of electrical connections which give off the largest amount of current. |
| Receiver. | An instrument in telephony and telegraphy which receives or takes in the sound or impulses. |
| Relay. | The device which opens or closes a circuit so as to admit a new current which is sent to a more distant point. |
| Repulsion, Electric. | That tendency in bodies to repel each other when similarly charged. |
| Resilience. | The springing back to its former condition or position. |
| Resistance. | The quality in all conductors to oppose the passage of a current. |
| Resistance Coil. | A coil made up of wire which prevents the passage of a current to a greater or less degree. |
| Resistance, Electrolytic. | The counter force in an electrolyte which seeks to prevent a decomposing current to pass through it. |
| Resistance: Internal, External. | The opposing force to the movement of a current which is in the cell or generator. This is called the internal. That opposite action outside of the cell or generator is the external. |
| Resonator, Electric. | An open-circuited conductor for electrically resounding or giving back a vibration, usually exhibited by means of a spark. |
| Rheostat. | A device which has an adjustable resistance, so arranged that while adjusting the same the circuit will not be open. |
| Safety Fuse. | A piece of fusible metal of such resistance that it breaks down at a certain current strength. |
| Saturated. | When a liquid has taken up a soluble material to the fullest extent it is then completely saturated. |
| Secondary. | One of the two coils in a transformer, or induction coil. |
| Secondary Plates. | The brown or deep red plates in a storage battery when charged. |
| Self-excited. | Producing electricity by its own current. |
| Series. | Arranged in regular order. From one to the other directly. If lamps, for instance, should be arranged in circuit on a single wire, they would be in series. |
| Series, Multiple. | When lamps are grouped in sets in parallel, and |
| Series Windings. | A generator or motor wound in such a manner that one of the commutator brush connections is joined to the field magnet winding, and the other end of the magnet winding joined to the outer circuit. |
| Shunt. | Going around. |
| Shunt Winding. | A dynamo in which the field winding is parallel with the winding of the armature. |
| Snap Switch. | A switch so arranged that it will quickly make a break. |
| Sounder. | The apparatus at one end of a line actuated by a key at the other end of the line. |
| Spark Coil. | A coil, to make a spark from a low electro-motive force. |
| Spark, Electric. | The flash caused by drawing apart the ends of a conductor. |
| Specific Gravity. | The weight or density of a body. |
| Static Electricity. | Generated by friction. Also lightning. Any current generated by a high electro-motive force. |
| Strength of Current. | The quantity of electricity in a circuit. |
| Synchronize. | Operating together; acting in unison. |
| Terminal. | The end of any electric circuit or of a body or machine which has a current passing through it. |
| Thermostat, Electric. | An electric thermometer. Usually made with a metal coil which expands through the action of the electricity passing through it, and, in expanding, it makes a contact and closes a circuit. |
| Transformer. | The induction coil with a high initial E. M. F. changes into a low electro-motive force. |
| Unit. | A standard of light, heat, electricity, or of other |
| Vacuum. | A space from which all matter has been exhausted. |
| Vibrator. | Mechanism for making and breaking circuits in induction coils or other apparatus. |
| Volt. | The unit of electro-motive force. |
| Voltage. | Electro-motive force which is expressed in volts. |
| Voltaic. | A term applied to electric currents and devices. |
| Volt-meter. | An apparatus for showing the difference of potential, or E. M. F. in the term of volts. |
| Watt. | The unit of electrical activity. The product of amperes multiplied by volts. |
| Watt Hour. | One watt maintained through one hour of time. |
| Waves, Electric Magnetic. | Waves in the ether caused by electro-magnetic disturbances. |
| X-rays. | The radiation of invisible rays of light, which penetrate or pass through opaque substances. |
| Yoke, or Bar. | A soft iron body across the ends of a horseshoe magnet, to enable the magnet to retain its magnetism an indefinite time. |
| Zinc Battery. | A battery which uses zinc for one of its elements. |
