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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.

FIG. 1.—A simple Wimshurst Machine which any boy can easily make. P P, Plates; BR, Neutralizes; C R, Collectors; DR, Discharge Rods; J J, Leyden Jars; H H, Insulating Handles; C, Crank; U, Upright; B, Belt.

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".

FIG. 2.—The plates for the Static Machine are made of hard rubber and are 7 inches in diameter. Each plate carries sixteen tinfoil sectors.

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.

FIG. 3.—The details of the Tinfoil Sector. Sixteen are required for each plate. They are stuck to the plates with shellac.

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.

FIG. 4.—Details of the Grooved Pulley, attached to each plate. The Pulleys are turned out of wood.

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.

FIG. 5.—The base of the Wimshurst Machine. All woodwork about the machine should be carefully dried and then shellaced so that it cannot absorb any moisture.

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.

FIG. 6.—Details of one of the Uprights which support the Plates, Driving Pulleys, etc. These, being made of wood, should also be dried and shellaced so that they cannot absorb moisture.

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.

FIG. 7.—Showing the Two Uprights in position on the Base.

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.

FIG. 8.—The Driving Pulleys. These are turned out of wood and mounted on a shaft having a Crank at one end.

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.

FIG. 9.—The Crank is bent out of a piece of 3/16 rod, 7 inches long, into the shape shown.

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.

FIG. 10.—The Collector with the Discharge Rods, etc, in position. A is the Brass Ball forming one terminal of the gap across which the sparks jump. B is another Brass Ball screwed onto the end of the Collector Rod and having a hole in it, through which the Discharge Rod slips. CC are two threaded Washers used to clamp the Discharge Rod in place.

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.

FIG. 11.—Showing how Binding Posts may be substituted for Round Balls on the Collector Rods.

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.

FIG. 12.—Details of the Discharger Rods.

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