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A Leyden Jar is a very simple device for accumulating and storing static electricity. It consists simply of a wide mouthed jar or bottle coated with tinfoil part way up on both the outside and the inside in exactly the same manner as the small test tubes used on the static machine.

Not all glass jars are suitable for making Leyden Jars. The quality of the glass varies considerably and some will be found far superior to the rest.

The glass vessels used by chemists and called "beaker glasses" usually make excellent Leyden Jars.

It is not very difficult to make a good Leyden Jar. After you have selected the jar or bottle you wish to use, clean and dry it very thoroughly. Then give the inside a thorough brushing over with shellac. Cut a strip of tinfoil which is long enough to go all the way around the inside of the jar and about two-thirds its height. Before the shellac is thoroughly dry but is still sticky, insert the tinfoil strip carefully into the jar and press it smoothly against the glass.

FIG. 13.—The Supporting Bar upon which the Collector Rods are mounted. Made of hard rubber so as to be a perfect Insulator.

The outside of the jar should also be given a coat of shellac and covered with tinfoil in exactly the same manner. The tinfoil on the outside of the jar should be the same height as that on the inside. The bottom of the jar should be coated, both inside and out by cutting two circular pieces out of the tinfoil and sticking them on with shellac.

The jar should be provided with a wooden cover which will fit snugly into the top. The wood should be dried and then given a coat of shellac so that it cannot absorb any moisture.

FIG. 14.—The Neutralizers. Two are required. They are bent out of Brass Rod and fitted with a Tinsel Tuft at each end. The centre piece upon which the Rod is mounted should be of Hard Rubber.

It may perhaps be well at this point to emphasize how highly important it is to always keep all static electrical apparatus thoroughly dry and to construct it so that it will not collect or absorb any moisture.

A small hole should be bored through the centre of the cover so as to permit a brass rod to pass through. A piece of spring wire bent into a spiral should be attached to the lower end of the rod. When the cover is in position, the spring wire should make contact with the tinfoil on the inside of the jar.

It is a very good idea to fit the top of the rod with a small brass ball. This will prevent the electricity from "leaking" from the sharp corners on the end of the rod. Static electricity leaks very easily from sharp corners or points, but does not escape so readily from round corners or balls.

FIG. 15.—Details of the Leyden Jars. They are simply small Test Tubes, coated inside and outside with tinfoil for about two-thirds their height and fitted with a Brass Rod connected with the inside coating.

The Leyden jar may be "charged" with electricity from the static machine by connecting a wire from one of the discharge rods to the outside tinfoil coating on the jar. Another wire should be connected from the other discharge rod to the rod on the jar which connects with the inside tinfoil coating.

Turning the handle of the machine rapidly for ten or fifteen seconds will charge the jar. Disconnect the wires as promptly as possible so that the electricity in the jar will not have a chance to leak back into the machine. Be very careful while doing this, however, because if you should happen to touch the tinfoil on the outside of the jar and the rod which connects with the inside coating at the same time you will get one of the surprises of your life.

FIG. 16.—A Large Leyden Jar for experimental purposes.

The shock won't really hurt you any but it will be very uncomfortable and somewhat surprising.

You can discharge a Leyden jar by bringing a piece of wire which is connected to the outside coating, near to the knob on the rod. When the wire is close to the ball the electricity will jump across the space in the shape of a snapping white spark.

The Leyden jar can be used in connection with a number of experiments described later on.

FIG. 17.—Showing how to Discharge a Leyden Jar with a curved piece of stiff wire fitted to a Wooden Handle.

Bottled Lightning. A very pretty effect can be obtained by passing the spark from a Leyden jar or a static machine over a "lightning board." A "lightning board" consists of a pane of glass having a number of small squares of tinfoil stuck on it so that when the electrical discharge is passed over it, sparks take place between the little tinfoil squares and produce an effect something like miniature lightning.

A lightning board suitable for the static machine just described may be made from a strip of ordinary window glass about nine inches long and two inches wide.

Clean the glass thoroughly and then give it a coat of shellac on one side. As soon as the shellac becomes sticky, lay on a strip of tinfoil the same size as the glass and rub it down smoothly. When the shellac has thoroughly dried so that the tinfoil is stuck tightly to the glass, the board is ready to be cut up into squares. This can be best accomplished by means of a sharp knife and a ruler. Use care in doing the work so as not to tear the tinfoil and be sure that the knife cuts all the way through to the glass. Leave two solid strips of tinfoil at each end to which to make connections.

FIG. 18.—The "Lightning Board" is simply a Strip of Glass covered with small Tinfoil Squares. It may be insulated by mounting on a Bottle. The two Wires attached to the wide Tinfoil Strips at the ends of the "Board" are for connection to the Static Machine or Leyden Jar.

The lightning board should be mounted by cementing it in a slot in a cork in a bottle so that the glass bottle serves as an insulated support.

If one of the tinfoil strips left solid at the end of the board is connected to one of the discharge rods on the static machine and the other end is connected likewise to the other discharge rod innumerable little sparks will zig-zag between the tinfoil squares when the machine is set in operation. The effect is quite pretty if the experiment is performed in a dark room.

The Leyden jar can be charged by the static machine and discharged through the lightning board. The sparks produced by the Leyden jar will be much more brilliant than those of the static machine above.

A very pretty effect can be produced by arranging the tinfoil in the form of a pattern or design as for example that illustrated in Figure 19. A strip of glass about the same size as that used for the lightning board may be employed. The glass is coated with shellac and as soon as it becomes sticky, small rectangular pieces of tinfoil arranged in a zig-zag pattern and having small spaces between them, are stuck in position. The end pieces are made larger than the other strips so as to afford means for connecting the wires. The strip should then be insulated and mounted by cementing it in a slot in the cork of a glass bottle.

FIG. 19.—A very pretty effect can be produced by arranging small tinfoil strips on the Glass in a Pattern. Each strip should be separated from the other just far enough for a Spark to pass.

The apparatus shown in Figure 20 is made according to the same plan but the glass in this case is in the form of a square instead of a strip. The tinfoil strips are arranged in the form of a seven pointed star or any other pattern which may be desirable. The two large strips A and B are the ones to which the wires should be connected.

The Electric Parasol is illustrated in Figure 21. It is made by pasting some narrow strips of tissue paper, about three-sixteenths of an inch wide and three or four inches long, to a small cork which has previously been covered with tinfoil. The strips can be made most easily by cutting a small sheet of tissue paper into strips like the teeth of a comb as shown in the upper right hand corner of Figure 21. The tinfoil covered cork should be mounted on the upper end of a stiff copper or brass wire supported in a bottle.

If this wire is then connected to one of the discharge rods on the static machine and the hand held to the other, the paper strips will spread out like a parasol or umbrella, as soon as the machine is set in operation.

FIG. 20.—A very pretty design made by arranging the Strips in the form of a Seven-pointed Star. Flowers, initials or almost any pattern may be made in the same way.

A novel experiment somewhat similar in principle to the "electric parasol" is that shown in Figure 22.

Three small paper birds about the size of that shown at the right hand side of the illustration should be cut out of tissue paper and each one attached to a piece of cotton thread about six inches long. The threads are then tied to one end of a T-shaped frame bent out of copper wire and supported on a bottle.

If the wire frame is then connected to one of the discharge rods and the hand held to the other while the machine is set in operation, the birds will rise in the air and fly around as far as the threads will let them.

FIG. 21.—The Electric Parasol. The upper right-hand corner shows a piece of Tissue Paper cut into Strips. (1) Is the apparatus before the Tissue Paper is fastened to the Cork. (2) Shows the completed "Parasol" and (3), the Parasol when connected to the machine and the latter is set in operation.

Electric Acrobats. The apparatus shown in Figure 23 consists of a circular metal plate about four inches in diameter suspended by a wire from a wire "T" stuck in a cork in a bottle. Another circular metal plate of the same size is laid on the table below the other. The distance between the two plates should be about one inch or an inch and one-half.

Cut three or four little figures, the same size as that shown in the upper right hand part of the illustration, out of tissue paper and lay them on the bottom plate.

FIG. 22.—Electric Birds. The Birds are made of Tissue Paper and should be about the size and shape shown in the lower right-hand corner of the illustration above.

The circular metal plates may be made of sheet tin, copper, brass or galvanized iron. Even cardboard, provided that it is covered with tinfoil, will serve.

The upper plate should be connected to one discharge rod on the static machine and the lower plate to the other. Then as soon as the machine is set in operation the little paper figures will begin to dance up and down, stand on their heads, hang by one foot or hand, turn somersaults and perform all sorts of stunts.

Gunpowder may be ignited by the spark from a Leyden jar. A miniature mortar may be made from a piece of broom handle about an inch and one-half in diameter with a hole one inch deep in one end as shown by C Figure 24. The mortar should be fastened to a small wooden base which will support it in an inclined position as in the illustration.

FIG. 23.—Electric Acrobats. The Acrobats are made of paper. The little figure in the upper right-hand part of the illustration is the proper size.

Bore two small holes through the wall of the mortar, near the bottom and exactly opposite to each other Insert two short pieces of coper wire, W, W, in the holes and fasten them tightly in position. The ends of the wires should be about one-eighth of an inch apart.

A small pinch of gunpowder is then placed in the bottom of the mortar.

Charge the Leyden jar and then discharge it through the mortar by connecting it to the two wires W, W. As soon as the spark passes, the powder will explode. An experiment such as this should be performed cautiously and the face and hands should be kept away from the powder. Do not put more than a pinch of powder in the mortar at a time and by all means keep the reserve supply out of the way so that there will be no danger of exploding it by accident.

An Electric Whirligig is an interesting piece of apparatus which may be built by following the suggestions contained in Figure 25.

FIG. 24.—The Electric Mortar. C is the Mortar, P the Powder, B a Small Ball and W W the two Wires between which the Spark igniting the powder takes place.

Mount four pieces of dowel about three inches long at the corners of a wooden base about eight inches long and two inches wide so that they form four vertical posts as shown by A, B, C, D.

The dowels, as well as the wooden base should be carefully dried and shellaced so that they will not absorb any moisture.

Stretch two pieces of straight stiff wire between the posts A C and B D, near the top. The wires should be perfectly straight and level.

The whirligig itself is made by passing a sewing needle through the axis of a small cork. Four small wires having the ends bent over at right angles should then be stuck in the cork as shown in the upper left hand part of Figure 25. All of the wires should point in the same direction.

FIG. 25.—An Electric Whirligig.

The four wires should all be the same length so that the whirligig is perfectly balanced. The cork is then covered with tinfoil so that there will be an electrical connection between the four small wires and the needle forming the shaft.

The two wires A C and B D are connected together by a wire A B and a piece of flexible wire led to the Wimshurst machine. The opposite side of the Wimshurst machine is then grounded or touched with the hand. If the whirligig is laid on the wires A C and B D as shown in the illustration and it is perfectly balanced it will commence to revolve and roll along the wires just as soon as the Wimshurst machine is set in operation. It is the escape of the electricity from the points of the four wires on the whirligig which causes this.

Other interesting experiments in static electricity may be performed with the aid of a Wimshurst machine and the experimenter who is sufficiently interested to continue farther is referred to any good book on physics or some such volume as "The Boy Electrician".