Thomas M. St. John

“ The power that a piece of steel has to hold magnetism is called retentivity. Different kinds of steel have different retentivities. A sewing-needle of good steel will retain magnetism for years, and it is almost impossible to knock the magnetism out by hammering it. Soft steel has very little retentivity, because it does not contain much carbon. Soft iron, which contains less carbon than steel, holds magnetism very poorly; so it is not used for permanent magnets. A little magnetism, however, will remain in the soft iron after it is removed from a magnet. ”

“ In our study of magnetism you learned that a magnet can act through the air, and induce a piece of iron to become a magnet. You saw how the iron filings arranged themselves around the magnet, showing that the lines of force reached out from the poles in a very peculiar manner. There is an electric field all around a charged conductor, just as there is a magnetic field about a magnet. The lines of force in the electric field pass from the positively charged body to the negatively charged one, or to some neutral one, which, you will soon see, is practically the same thing. ”

“ Electro-Magnets are absolutely necessary in the construction of most pieces of electrical apparatus. There are several ways of making them at home. To quickly make a good-looking one, a winder (App. 93) is required. We shall divide our electro-magnets into four parts: Core, washers, insulation, and coil.
Of course, you know that when a current of electricity passes through a wire, a magnetic field is produced around the wire. A coil of wire, or helix, has a stronger field than a straight wire carrying the same current, because each turn or convolution adds its field to that of the other turns. ”

“ When a spark of static electricity jumps a long distance, we say that the charge has a high potential; that is, it has a high electrical pressure. Potential, for electricity, means the same as pressure, for water. The greater the potential, or electromotive force (E.M.F.) of a cell, the greater its power to push a current through wires. (See "Study," § 296 to 305, with experiments.) ”

“ Spark. Electrification will easily pass from a place of high potential to one of low potential through a conductor, and when it passes we say we have an electric current, or a current of electricity. Water has no desire to flow on a dead level, and the electric current does not care to flow between two places of equal potential. The potential of the earth and of all neutral bodies is zero; that is, they have no charge, no potential; so it is very easy for a charge to escape into the earth. ”

“ In Dynamotors the motor and dynamo armatures are combined in one, thus requiring a single field only. The primary armature winding, which operates as a motor to drive the machine, and the secondary or dynamo winding, which operates as a generator to produce a new current, are upon the same armature core, so that the armature reaction of one winding neutralizes that of the other. They therefore have no tendency to spark, and do not require shifting of the brushes with varying load. Having but one field and two bearings, they are also more efficient than motor-dynamos. ”

“ Popular Pastimes are numerous, but to many there is nothing more fascinating than photography. The magic of sunshine, the wonders of nature, and the beauties of art are tools in the hands of the amateur photographer. If you want to get a start in this up-to-date hobby, this outfit will help you. You will enjoy the work and be delighted with the beautiful pictures you can make. ”

“ If the potential of a body becomes greater than that of the earth, the body is said to be positively electrified; if the potential of the body is less than that of the earth, it is said to be negatively electrified. If we fill a bottle with sea water, we have a great deal of water when we compare it with the bottle, but a very little water when we compare it with the sea. The earth is so large that small amounts of electrification taken from it or added to it do not affect its potential to any extent. ”

“ When the motorman turns the handle of the controller to the first notch, the current passes through all of the resistance wires placed under the car, then through one motor after the other. The motors being joined in series by the proper connections at the controller, the greatest resistance is offered to the current and the car runs at the slowest speed at this first notch. As more resistance is cut out by turning the handle to other notches, the car increases its speed; but as the resistance wires become heated and the heat passes into the air, there is a loss of energy. ”

“ Every Boy Should Make Electrical Toys.
A MOTOR THAT CAN DO THINGS
The "St J. Motor No. 1" (List No. 2201) is designed for students and others who want a small motor for experimental purposes as well as for all of the work that any small motor can do. We believe this to be the best small motor made, and we know that it can be used in more ways than any other motor of equal cost ever built. It has four binding-posts,—making it possible to energize the field or armature separately,—and so it can be used in circuits with reversers and rheostats for experiments. ”

“ It is harder for a horse to draw a wagon through deep sand than over a smooth pavement. We may say that the sand holds the horse back—that is, it offers a resistance. The electric current does not pass through all sorts of substances with the same ease, and when it succeeds in pushing its way through a circuit of considerable resistance, we cannot expect it to arrive at the end of its journey without being weaker than when it started. ”

“ Each little particle of a piece of steel or iron is supposed to be a magnet, even before it touches a magnet. When these little magnets are thoroughly mixed up in the steel, they pull in all sorts of directions upon each other and tend to keep the steel from attracting outside bodies. When a magnet is properly rubbed upon a bar of steel, the north poles of the little molecular magnets of the steel are all made to point in the same direction. As the north poles help each other, the whole bar can attract outside bodies. ”

“ Chemistry is universally considered to be an interesting subject, even in school, and it is certainly an important one in these days of scientific progress. This outfit starts you at the right place and presents the elements of the subject in a most interesting fashion. The experiments are so enjoyable that you will take pleasure in doing them over and over again, and you will want to do them for your friends. You can have a lot of fun with this set, and even if you have taken advanced courses in the subject you will find something new in these experiments. ”

“ They become charged by chemical action, and not by friction. The zinc is gradually dissolved, and it is this chemical burning of the zinc that furnishes energy for the electric current in the simple cell. The electrification, or charge, on the plates tends to flow from the place of higher to the place of lower potential, just as water tends to flow down hill. If a wire be joined to the two metals, a constant current of electricity will flow through it, because the acid continues to act upon the plates. The simple cell is a single-fluid cell, as but one liquid is used in its construction. ”

“ Electrification is, then, a sort of potential energy.
104. Heat and Electrification. We say that heat passes to or from a body to make it hot or cold. Heat produces the sensation of warmth, but heat isn't warmth. We can force a cold body to become hot; in other words, we can get it into a hot condition in various ways, such as rubbing it, hammering it, or by placing it near or in contact with another hot body.
Electrification is, also, a condition or state into which we can force a body; but electrification isn't electricity. ”

“ An Electric Motor is really a machine. If it be supplied with a proper current of electricity, its armature will revolve; and, if a pulley or wheel be fastened to the revolving shaft, a belt can be attached, and the motor made to do work. There are many kinds of motors, and many simple experiments which aid in understanding them. ”

“ The Electric Motor is a machine for transforming electric energy into mechanical power. The construction of motors is very similar to that of dynamos. They have field-magnets, armature coils, commutator, etc.; in [149] fact, the armature of an ordinary direct current dynamo will revolve if a current be passed through it, entering by one brush and leaving by the other. There are many little differences of construction, for mechanical and electrical reasons, but we may say that the general construction of dynamos and motors is the same. ”

“ Lightning may be produced by the passage of electricity between clouds, or between the cloud and the earth, which, with the intervening air, have the effect of a condenser. If one cloud is charged, it acts inductively upon another, producing in it the opposite kind of electrification. When the attraction between the two electrifications becomes great enough, it overcomes the resistance of the air, and lightning is produced. ”

“ Bubbles of hydrogen gas are formed when zinc is dissolved by an acid. In the ordinary simple cell these bubbles collect on the copper plate, and not on the zinc plate, as might be expected. The hydrogen is not a conductor of electricity, so this film of gas holds the current back. The hydrogen acts like a metal and sets up a current that opposes the zinc to the copper current. ”

“ You have seen that the horseshoe magnet can lift nails, iron filings, etc.; you have used this lifting power to show that the magnet was really a magnet, and not merely an ordinary piece of iron painted red. Can we give some of its magnetism to another piece of steel? Can we pass the magnetism along from one piece of steel to another? ”

“ If a piece of steel or iron, like a stove poker, for example, be held in a north and south line with its north end dipping considerably, it will be in the best position for the magnetism of the earth to act upon it ”

“ We know whether a body is hot or cold by its effects upon us, upon thermometers, and upon other bodies. We can tell, also, whether a body is electrified or not by the way it acts, and, in certain cases, by the sound, heat, and light which accompany the electrification. ”

“ An induced current, produced as in the above experiment, is a momentary one. No current passes when the magnet and coil are still; at least one of them has to be in motion. When the magnet is inserted, the induced current is said to be an inverse one, as it passes in a direction opposite to that which would be necessary to give the magnet its poles, it being considered [180] a core magnetized by the current. A direct current is produced when the magnet is withdrawn from the coil. Rapid movements produce stronger currents than slow ones. ”

“ Force; Resistance; Work; Potential Energy; Electrification. It takes force to raise water into a tank placed on the roof. In raising the water, work has to be done, and we have to do the work; but when we once have the water in the tank we have accomplished something. The water has potential energy; that is, on account of its high position, we can make it do some work by simply turning a stop-cock so that the water can run out and turn a water-wheel, for example.
It takes force to vigorously rub a piece of ebonite with a flannel cloth, for resistance has to be overcome ”

“ A condenser can hold much more electrification at a certain potential than an equal amount of surface can hold when not properly arranged. We might call a condenser a storage battery for static electricity. The capacity of a condenser depends, among other things, upon the area of the conducting surfaces, and upon the thickness and nature of the dielectric. ”

“ There is very little loss of energy in well-made transformers. They consist of two coils of wire on the same core; in fact, an induction coil may be considered a transformer. If the secondary coil has 100 times as many turns of wire as the primary, a current with an E. M. F. of 100 volts can be taken from the secondary coil, when the E. M. F. of the current passing through the primary is 1 volt; but the strength (amperes) of the secondary current will be but one-hundredth that of the primary current. ”

“ The action here was like that in the previous experiment, the difference being that a longer conductor was used. Electrification is always looking for some place to get to the earth, just as water will run from a roof to the ground. You will understand more about it a little later. In our apparatus just described, the only way that the earth could be reached was through the wooden rod S R. Do not get the idea that real messages are sent in any such way, or that electricity flows through a wire as water flows through a pipe. ”