Donald M. Bliss.

Four methods of connecting electrical devices cover most of the field in engineering practice. Figs. 5 and 6 show two methods of connection which will be used most frequently by the experimenter. The Fig. 5, known as a series connection, shows the zinc or negative pole of one cell connected to the positive or carbon pole of its neighbor. The cells are all connected up in this manner as shown, leaving an unconnected positive pole at one end of the series and a negative pole at the other. This method of connection has the effect of adding the pressure of the cells together, so that the total pressure of the series is that of one cell multiplied by the number of cells so connected. For instance, if the pressure of the single cell is 21/4 volts, the pressure of the six cells connected in a series will be 131/3 volts. While the pressure.or voltage is thus increased, it should be borne in mind that the total available current in amperes is only that of a single cell.

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Fig. 6.

The amount of current that can be obtained in such a battery depends on the size of the negative and positive elements, and on the electrical resistance of the solution used in the battery. If it is desired to obtain from these cells the greatest amount of current, regardless of voltage, they must be connected in the manner shown in Fig. 6, known as the multiple, or parallel, grouping. Tn this instance it will be noted that all the positive poles are connected together by an independent wire, and all the negative poles by another wire. The difference of pressure or voltage from one of the connected wires to the other is evidently only that of a single cell, say 21/4 volts. As all the positive plates are connected together to one wire, and all the negative plates to the other, the battery then becomes the same in effect as a single large cell, having positive and negative elements, or plates, six times the size of a single cell. The available current is therefore six times as great, and the voltage of pressure one-sixth that of the series connection shown in Fig. 5.

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Fig. 7.

While we are on the subject of connections, it will be well to illustrate the matter still further by reference to the most frequently used methods of connections in electric-lighting circuits. Fig. 7 shows the usual form of connection in series arc systems generally used for street lighting. The circles represent arc lamps in which the connections join one lamp in a series with another, so that the whole group of six lamps are in series connection with each other. If one lamp requires a voltage or pressure of about 50 volts, the six will require a total pressure of 300 volts, to operate them properly. As many as fifty lamps are sometimes connected in a series in this manner, and it will be seen that a total pressure of 2,000 to 3,000 volts may be necessary to operate a large number of arc lamps ; and as the current becomes dangerous at about 500 volts, it can readily be seen why fatal accidents are occasionally met with on street-lighting circuits.

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Fig. 8.

Fig. 8 shows the parallel, or multiple, connection generally used for incandescent lighting. In this case we have six lamps connected together across the main wires, or leads. As the standard incandescent lamp requires about 110 volts to operate properly, this pressure is maintained across the leads A and B. Each 16-candle-power lamp requires a current of approximately one-half an ampere at a pressure of 110 volts. The six lamps will therefore require one-half multiplied by six, or three amperes, to operate the group. As there are frequently many hundred lamps so connected, it will be seen that while the total pressure of such a system may not exceed 110 volts, the current may reach several hundred amperes in each main circuit. As a matter of fact, the total current output of some of the largest stations operating in this system reaches many thousand amperes.

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Fig. 9.

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Fig. 10.

The two methods of connection, series and multiple, cover most of the connections used in electrical engineering.

There are two other arrangements of circuits sometimes used, which are illustrated in Figs. 9 and 10, Fig. 9 showing what is termed a series multiple, or series parallel, method connection. In this arrangement it will be seen that the whole circuit consists of a series of groups of lamps, batteries or instruments, the members of each group being in multiple, while "Fig. 10 shows the multiple series system, in which the devices as a whole are connected in multiple, but divided into groups in which the devices of each group are in series with each other. It is of course understood that these methods of connection may be used with any electrical device, whether it be a battery, lamp or other appliance. In most of the experiments to • be described, the plain series connection will be found the most desirable.

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Figs. 11 and 12.

Figs. 11 and 12 show an electro-magnet of a suitable size to give the best results from the battery described in the previous article. This magnet will be very convenient for making permanent magnets and a variety of experimental work, including a study of magnetism and the magnetic field. The magnet consists of two spools, A and B, of the dimensions shown, securely fastened to a wooden base, C, by means of screws passing through the heads of the coils into the base. It will be noted that the spool-heads are square and thick. This substantial construction is necessary, because the device when completed is quite heavy and is subject to considerable handling. The spool-heads should be sawn from hard wood, and the center holes drilled seven-eighths of an inch in diameter. Two tubes of-several turns of-heavy manilla paper or cartridge paper, formed around a three-quarter-inch rod, should next be made. These tubes should be glued securely into the,. heads of the spool, as shown. Care should be taken to see that the heads are all square with each other and the same distance apart. This alignment may be best secured by fastening the. spool to a strip of wood while the glue is drying The holes for the fastening screws, and all other holes, should be drilled before the spool is wound. When this has been done, the spools may be mounted on a wooden arbor in the lathe, and wound.

Begin winding by inserting one end of the wire through the inner hole in the head E, and wind the wire on smoothly, layer after layer, until half of the wire has been wound on the spool. If the winding is not sufficiently smooth when the last two layers are being wound, a strip of stiff paper may be fitted around the spool and the last layer wound over the paper, making a smooth finish. The ends should be left long enough to connect to the binding screws, F and G, as shown. Connect the inside end of each coil together, and you may then make the core H. This is made from a three-quarter-inch bar of soft iron bent into the U-shape shown. This core, to give the best results, should be annealed by heating it red hot and allowing it to cool slowly. Do not fasten the coils to the base until the iron core has been made, for if the distance between the arms of the core does not come out according to the sketch, the position of the coils on the base will be altered accordingly. The winding may consist of two pounds of No. 18 B. & S. (Brown & Sharpe) gauge single cotton covered magnet wire. After the magnet has been completed, the coils may be given one or two coats of shellac varnish, and when.dry the magnet is ready for use. The iron core should slide freely through the coils, as it will be found necessary to remove it in various experiments. To hold the core firmly in position, when fequired, two wood strips, hollowed out to fit the core, as shown at H, may be used. These strips, if screwed securely to the base, will hold the core firmly in position.

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Fig. 13.

Fig. 13 shows a key, or circuit closer, which will be found most convenient for making and breaking the connection of the battery. It should be made as described on page 16, in the November number of this magazine.

Another device for rapidly interrupting the circuit is shown in Fig. 14. This will be found convenient for giving shocks in connection with the electro-magnet, for experiments with induction coils, and a variety of other uses. It is very easily constructed, and the amateur should not neglect to provide himself with such an interrupter. It consists.simply of a wooden wheel turned in one piece with its shaft. This wheel is mounted between two uprights on the base B. Before the wheel is taken out of the lathe, a circle should be marked on each side of it, and around this circle a number of wire nails should be driven through the wheel, so as to extend equally on each side. Two flat brass springs provided with connection crews may be fastened to the base of opposite ■ides of the wheel, so that they will both bear gently at once on the pin which happens to be at the lower diameter of the wheel, as shown. The wooden shaft on one side of the wheel may be extended through the wooden upright or bearing, F, and provided with a small crank or hand-wheel, so that it may be easily turned. It will now be seen that as the wheel is revolved, the connection between the springs will alternately be made and broken as the device is operated. It will be found convenient to provide the handwheel G with a groove on its edge, so that, if necessary, it may be driven by a belt by any convenient ■ource of power, such as a small motor run from ft battery.

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Fig. 14.

The proper connection for the battery, magnet and key, or circuit closer, is as follows : The wire is run from one pole of the battery to one of the binding posts on the base of the magnet. Another connection is made from the second binding post on the magnet to one of the connections on the key. The remaining connection on the key is connected with the other pole of the battery. In order to preserve the condition of the battery as long as possible, it is important at the conclusion of all experiments that the circuit be left open and the battery plates be removed from the jars.. If this is not attended to, the battery will rapidly lose its strength, and solution will require frequent renewal, and the zincs cleaned and amalgamated; i. e., treated with the mercury as described in the-preceding article.