How to Build a Wimshurst Machine.

Static electricity and lightning are the same thing.

A boy can produce static electricity in small quantities by rubbing a glass rod with a piece of flannel or silk.

Rub the rod briskly and then hold it over some tiny bits of paper or specks of dust and watch them jump up to meet the rod, just as if the latter were a magnet attracting small tacks or nails. It is static electricity which gives the rod this wonderful power. If you rub the rod briskly and then hold it close to your cheek, you will feel a slight tickling and hear a faint crackling sound. If this is done in the dark you may be able to see a very faint phosphorescent light or even small sparks.

The quantity of electricity produced in this manner by rubbing a glass rod is extremely limited and while a number of very interesting and instructive experiments may be performed in this manner, the most spectacular ones are only possible with the aid of a "static-machine".

The most practical form of static machine is that known as the "Wimshurst". It consists of two circular plates made of glass or hard rubber arranged so that by turning a crank, they may be revolved in opposite directions. On these plates are a number of small strips of tinfoil. The static electricity is generated on these tinfoil strips and collected by two metal rods having small pins arranged along them in a row.

A simple form of Wimshurst machine which any boy can easily make is illustrated in Figure 1. It will generate considerable static electricity and will make sparks two inches long.

The Plates on these machines are hard rubber. They are illustrated in Figure 2. Glass is usually used for static machine plates, but has the disadvantage of breaking easily. It is also hard for the young experimenter to cut out circular glass plates and drill them. The author has had very good success with hard rubber.

Two plates are required for the machine. They should be in the form of circles seven inches in diameter and be perfectly true. They need to be only one-sixteenth of an inch thick. The rubber should be perfectly flat and not warped at any point.

The Sectors, as the tinfoil strips are called, are wedge shaped pieces having rounded ends as shown in Figure 3. They should be cut of heavy tinfoil. Thirty-two sectors are required, sixteen for each plate. They are seven-sixteenths of an inch wide at the top, one inch long and five-sixteenth of an inch wide at the bottom.

The plates should be very carefully cleaned by rubbing with a dry cloth and then laid on a flat surface all ready to receive the sectors.

The sectors should be stuck to the plates with thick shellac. They should be arranged all on one face, symmetrically and at equal distances apart, with the inner ends resting on a circle four and one-half inches in diameter. Each sector should be carefully pressed down on the rubber so that it sticks smoothly without any air bubbles or creases.

Both plates should be treated in the same manner.

The Pulley illustrated in Figure 4 is one inch in diameter and eleven-sixteenths of an inch thick. Two of these pulleys will be required. The hole through the centre should be about three-sixteenths of an inch in diameter. One pulley should be attached to each of the rubber plates. The large face of the pulley should be against the face of the plate upon which the tinfoil sectors are mounted. The hole in the centre of the pulley should line up perfectly with a hole of the same size in the centre of each one of the plates. The plates are fastened to the pulleys by three small brass nails driven into the wood through small holes in the rubber.

The Base of the machine is a rectangular shaped piece of wood six inches long, four inches wide and three-quarters of an inch thick. A notch, one inch wide and one-half an inch deep is cut in the centre of the front and back as shown in Figure 5. The purpose of these notches is to receive the uprights.

The Uprights are strips of wood, seven inches long, one inch wide and one-half an inch thick. The tipper end of each of the uprights is rounded as shown in Figure 6.

Two holes should be bored through each of the uprights from front to back. The lower hole is three-sixteenths of an inch in diameter and two and one-quarter inches from the bottom. The upper hole is six and one-half inches from the bottom and is between one-eighth and three-sixteenths of an inch in diameter so that a three-sixteenth rod driven into it will fit tightly.

The uprights should be mounted in position in the base and fastened with screws.

The plates are mounted between the upper ends of the uprights in the position shown in Figure 1, by driving a short piece of 3/16 round brass rod through the uprights into the holes in the centre of the pulleys. The rod used to mount the back plate should be one and one-half inches long and that used for the front plate one and five-eighths inches long. The 3/16 hole in the pulleys should be large enough so that the latter will revolve freely.

The plates are revolved by two driving pulleys provided with a crank for turning.

The Driving Pulleys are shown in Figure 8. They are not so easy to make as the small pulleys attached to the plates. They are turned out of wood and should be both alike. The exact shape and dimensions are shown in the illustration. The hole through the centre should be a scant three-sixteenths of an inch so that the pulleys will force onto a 3/16 rod very tightly.

The Crank is bent out of a piece of brass or steel rod about seven inches long. The straight portion, forming the shaft upon which the pulleys are mounted, is three and seven-eighths inches long. The portion at right angles to this, forming what is known as the "throw" of the crank, is one inch and seven-eighths. The part forming the crank handle is one inch and one-quarter long.

The driving pulleys are placed between the two standards with the small projecting portions or "bosses" nearest the uprights. The straight portion of the crank should then be slipped through the hole in the front upright and driven tightly into the driving pulleys. The driving pulleys should fit so tightly onto the shaft that they will not slip. The end of the shaft should project through the pulleys far enough so that is rests in the hole in the rear standard.

The holes in the uprights or standards should be just large enough so that the shaft will turn freely. The driving pulleys should be lined up so that the groove in each comes directly under the groove in the corresponding pulley attached to the plate above.

The Belts consist simply of heavy cotton cord. The rear belt should be crossed so that the rear plate runs in the opposite direction from the front plate when the crank is turned.

The electricity is collected from the sectors on the plates by two

Collectors. These are illustrated in Figure 10 and consists of a piece of 5/32 brass rod, about six inches long, bent into the shape shown. Two small tufts of "tinsel" are soldered to the U-shaped portion of the collector so that when the latter is placed in its proper position on the machine, they will brush against the tinfoil-sectors as they pass when the plates revolve.

The other end of the rod is threaded to fit into a hole in a small brass ball about three-eighths or one-half inch in diameter. Many experimenters may have difficulty in securing a suitable brass ball for this purpose. An ordinary binding post may be used instead. The hole in the bottom of a binding post is usually threaded to fit an 8-32 screw. The end of the rod is just the right size to receive an 8-32 thread and so there should be no trouble in getting the parts to fit. The brass ball is marked "A" in the illustration. The ball is preferable to the binding because it has no sharp corners from which the electricity might leak. Static electricity leaks from sharp edges or corners and they must always be avoided as far as possible in the construction of static apparatus.

The end of the rod where it screws into the ball or binding post should be threaded back for a distance of about three-quarters of an inch and two brass nuts screwed onto the rod. These nuts are marked "C" in the illustration.

The collectors are held in position by the supporting bar illustrated in Figure 13. This bar is made of a strip of hard rubber, five and one quarter inches long, five-eighths of an inch wide and three-sixteenths of an inch thick.

Three holes, each five-thirty-seconds of an inch in diameter, should be bored in the bar. One hole should be exactly in the centre and the other holes seven-sixteenths of an inch back from the end.

The centre hole is slipped over the end of the shaft which projects through the front standard supporting the plate and the bar fastened across the support at right angles like a cross by driving in two small brass nails or screws through holes made in the rubber for that purpose.

The threaded portion of the collector rods should be slipped through the holes near the ends of the hard rubber bar and clamped firmly in position by placing one of the nuts "C" on the back and the other on the front and tightening them up.

The exact position of the collectors is best understood from Figure 1. They are lettered C R in the illustration. The brass balls B are screwed onto the ends of the rods after the nuts have been tightened. Each of these balls should have a hole, one-eighth of an inch in diameter drilled through it at right angles to the collector rod. The hole provided in the binding post for the accommodation of the wire may be used in case binding posts are employed instead of the rods.

These holes are to accommodate the Discharge Rods, which are two round brass rods, one-eighth of an inch in diameter and three and one-half inches long. One end of each of the rods is fitted with a small brass ball.

The other end of each is provided with a small insulating handle. A No. 8003 Electrose Knob is just the thing. These knobs are provided with a threaded bushing so that they may be screwed onto the rod.

The proper position for the discharge rods is shown in Figure 1. By sliding the rods back and forth in the balls on the ends of the collectors, the distance between the balls on the ends of the rods may be varied.

The spark discharge from the machine, when the latter is completed, takes place between these balls.

The machine still remains to be fitted with the "neutralizers" and a set of Leyden jars.

The Neutralizers are illustrated in Figure 14. Two are required. They consist of a piece of one-eighth inch brass rod, six inches long, having the ends bent over at right angles so as to form a shallow U. The distance between the ends when bent should be about three and five-eights inches. A tuft of tinsel should be soldered to the ends of each of the neutralizers.

Each neutralizer rod is supported by a hard rubber washer three-quarters of an inch in diameter and five-sixteenths of an inch thick. In the centre of the washer a hole should be drilled, which will fit snugly onto the rods upon which the plates are mounted and revolve. The neutralizer rod passes through a hole in the upper part of the washer as shown in the illustration.

Before the neutralizers can be put into position it will be necessary to pull out the rods which support the plates so that the plates can be removed. The hard rubber washers supporting the neutralizers are then slipped over the rods so that one will come between each support and plate when the latter is put back into position. The rods should be turned so that the tinsel tufts touch the sectors. The rubber washers should fit snugly on the rods so that the neutralizer will stay in any position in which it is placed. The proper position for the front neutralizer is a little less than half way between vertical and horizontal as shown in Figure 1. The neutralizer behind the rear plate should be at right angles to that in front.

The machine is now all ready for operation. In order for it to operate satisfactorily it is necessary for it to be warm and dry. It is, therefore, a very good idea to thoroughly dry the woodwork and give it a coat of varnish or shellac so that it cannot absorb any moisture. It may be necessary to start the machine by rubbing a glass rod with a piece of flannel or silk and then touching the rod to some of the sectors. The handle of the machine should be turned from left to right, that is, in such a direction that the front plate revolves in the same direction as the hands of a clock.

If the machine is in proper working order a stream of small sparks should flow between the spark balls on the ends of the discharger rods, provided they are not over a half inch apart, when the crank is turned.

The spark can be intensified and lengthened by fitting the machine with two small Leyden jars.

The Leyden Jars are made from small test tubes three inches long. The inside of the tube should be coated with tinfoil to within about one inch from the top. The outside of the tube should be coated in the same manner for the same distance. The tinfoil can be secured to the glass with shellac.

The top of the Leyden jars is closed with an ordinary cork. A piece of heavy brass wire bent into the form of a hook should pass through the cork and make connection with the tinfoil on the inside of the tube. One Leyden Jar should be hung over each of the collector rods by means of the hook. The tinfoil coatings on the outside of the jars should be connected together by a piece of wire running across from one tube to the other.

The machine is now complete and ready for performing a number of very interesting experiments.

Experiments with Static Electrical Apparatus.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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".