Thomas M. St. John

“ 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. ”

“ 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. ”

“ It is evident, from the last 3 experiments, that lines of force will pass through iron whenever possible, on their way from the N to the S pole of a magnet. When the armature of a horseshoe magnet is in place, most of the lines of magnetic induction crowd together and pass through it rather than push their way through the air. Air is not a good conductor of lines of force; and the magnet has to do work to overcome the resistance of the air, when the armature is removed, in order to complete the magnetic circuit. This work causes a magnet to become gradually weaker. ”

“ 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. ”

“ 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. ”

“ 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? ”

“ 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. ”

“ 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 ”

“ Each has a higher potential than the acid, but their potentials are not the same. This electrification tends to pass from the place of higher to the place of lower potential, and the conducting wire allows this transfer to take place. As the difference of potential is kept up by the continued chemical action, the current is continuous, and not simply instantaneous, as in discharges of frictional electricity. As heat is produced by the burning of coal, so electrification is produced by the chemical burning of zinc. ”

“ Modern machines depend upon the principle of induction. The electrophorus (Exp. 68) is really a very simple form of induction machine. The potential of these machines is very great, as the spark may jump many inches. Thousands of Galvanic cells would be needed to make a spark an inch long. When the spark passes through the air it meets with an extremely high resistance, as air practically insulates ordinary electricity. This high resistance in the circuit reduces the strength of the current. While the potential is very high, the strength of the current is very low. (See Ohm's Law.) ”

“ 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. ”

“ A coil, or helix of wire, has a stronger field than a straight wire carrying the same current, because each turn, or convolution, adds its field to the fields of the other turns. By having a core of soft iron instead of air, wood, or other non-magnetic material, the strength of the magnet is greatly increased. The central core may be permanently fixed in the coil, or it may be removable. (See Apparatus Book, Chapter IX, for Home-made Electromagnets.)
397. Cores of Electromagnets. A strong magnet has more lines of force passing from its N pole through the air to its S pole than a weak magnet. ”

“ 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. ”

“ If a piece of unmagnetized steel be balanced and then magnetized, it will no longer remain horizontal; it will dip. Try this. Compass-needles are balanced after they are magnetized. Can you now see why the needle did not remain horizontal after its poles were changed? A piece of steel first balanced and then magnetized, has to have its S pole slightly weighted, as suggested by the line at S (Fig. 26 x) , to make it horizontal. The magnetic needle does not tend to dip at the earth's equator, because the lines of force of the earth are nearly horizontal at the equator. ”

“ Effects of Polarization. The hydrogen bubbles weaken the current in at least two ways. In the first place, hydrogen is not a conductor of electricity; so it holds the current back, as any other resistance would.
Secondly, acid acts upon hydrogen as it would upon another metal. When the copper plate becomes well covered with hydrogen, the acid cannot touch it; so we really have a hydrogen plate in the cell. Hydrogen acts very much like zinc in the acid; we say that it is more electro-positive than copper. ”

“ The strength of a current of electricity is measured also by the work that it can do, and it depends upon its rate of flow at the point measured. The strength may be determined from its magnetic, heating, or chemical effects. ”

“ To get practical results for commercial purposes we require a proper source of current, proper conductors, and proper apparatus to convert the motions into useful work. The motions given to the parts of the apparatus in the previous experiments are not suitable for commercial purposes, as they are in straight lines. A rotary motion is needed to do good work; and when this is applied to a shaft, belts can be used to run all sorts of machinery. (See Electric Motors.)
Fig. 148.
EXPERIMENT 189. Rotary motion with a hollow coil of wire and a permanent magnet. ”

“ The part spoken to is called the transmitter, and the part which gives the sound out again is called the receiver. Sound itself does not pass over the line. Although the same apparatus may be used for both transmitter and receiver, they are generally different in construction.
Fig. 165. 480. The Bell or Magneto-transmitter generates its own current, and is, strictly speaking, a dynamo that is run by the voice. You have seen, by experiments, that a current can be generated in a coil of wire by moving a magnet back and forth in front of its soft iron core. ”

“ A piece of thin steel can be magnetized more strongly in proportion to its weight than a thick piece, because the magnetism does not seem to penetrate beyond a certain distance into the steel. Thin steel may be magnetized practically through and through. A thick magnet has but a crust of magnetized molecules; in fact, a thick magnet may be greatly weakened by eating the outside crust away with acid. By riveting several thin bar or horseshoe magnets together, thick permanent magnets of considerable strength are made. ”

“ We should know something about iron and steel at the start, because we are to use them in nearly every experiment. The success with some of the experiments will depend largely upon the quality of the iron and steel used.
When we buy a piece of iron from the blacksmith, we get more than iron for our money. Hidden in this iron are other substances (carbon, phosphorus, silicon, etc.) ”

“ Some elements are actually repelled by a powerful magnet; these are called diamagnetic bodies. It is thought that all bodies are more or less affected by a magnet.
16. Practical Uses of Magnets. Many practical uses are made of magnets, such as the automatic picking out of small pieces of iron from grain before it is ground into flour, and the separation of iron from other metals, etc. The most important uses of magnets are in the compass and in connection with the electric current, as in machines like dynamos and motors. (See experiments with electro-magnets.) ”

“ The molecules of steel do not move about or change their relative positions as readily as those of soft iron. When the molecules of hard steel are once arranged, by magnetizing them, for example, they strongly resist any outside influences which tend to mix them up again.
A magnet does not attract a piece of red-hot iron. The particles of the hot iron are supposed to vibrate too rapidly to be brought into line; that is, the iron cannot become polarized by induction. ”

“ The air in the path of the electricity becomes intensely heated; it is this effect, and [85] not the electricity which we see. In hot weather flashes are often seen which light up whole clouds, no thunder being heard. This is called heat lightning, and is generally considered to be due to distant discharges, the light of which is reflected by the clouds.
The potential of the lightning spark is beyond all calculation. The spark jumps through miles of air, which is, really, an insulator. This spark represents billions and billions of volts. ”

“ It seems to pile up at points and corners, and we say that it is denser at such places than at well-rounded parts of a charged conductor. All points and sharp places should be removed from a conductor, if it is desired to keep a charge for any length of time.
Electrification may escape from a point so rapidly that currents are produced in the surrounding air. As the particles of air become charged, they repel each other. The movement of the air particles may be so great that a lighted candle will be affected when placed near the point. This current of air is called electric wind. ”

“ With the game-board are furnished, magic wands, polished steel balls, an "extra strength" horseshoe magnet, and a complete set of illustrated rules and directions for playing.
"Unlike all other games." "Any one can play Hustle-Ball." "Just the thing for progressive parties." "Hustle-Ball games are intensely exciting." "No waiting for some one to play." "You win or lose a point in a few seconds." "By handicapping the best players, all games are made equally interesting and exciting." ”

“ Two substances may be equally good insulators, that is, they may equally well resist the spread of electrification over their surfaces, or the flow of the electric current through them, while one may be, nevertheless, a better dielectric than the other. ”

“ When certain combinations of metals become hotter or colder, a current is produced. Voltaic or Galvanic electricity is produced by chemical action. Batteries give this variety. Induced electricity is produced by other currents, and by combinations of magnets and moving coils of wire, as in the dynamo. This is, by far, the most important variety of electricity, and the dynamo is the most important producer of it.
Each of the above varieties of electricity will be studied experimentally with simple apparatus.
EXPERIMENTS 51–52. To study electrification by friction. ”