There is no adjunct of the influence machine that affords a prettier or more striking experimental demonstration of electrostatic attractions and repulsions than an oscillating static motor.

In view of the dependence of the action of all ordinary types of electric motors upon magnetic influences, the curious little machine here illustrated is truly unique; for though an electric motor in the purest sense of the term, yet it derives its motions from forces that are wholly non-magnetic. With the aid of the working drawings and the hints here given, the amateur may easily construct for himself an experimental static motor whose action will be highly gratifying and instructive.

Fig. 197 - Side elevation of the motor.

A horizontally oscillating lever, a, of round vulcanite rod, carrying at its extremities two hollow halls, b and b'. of soft pine, communicates its motion through a slender vulcanite connecting rod, c, to a light flywheel, d, of thin wood. The lever, a, passes tightly through a turned wooden hub, e, into whose lower end is inserted a pivot rod, /, of steel wire, slightly under 1/8 inch in size. The lower portion of f, whose end terminates in a sharp point, turns freely in a vertical socket, g, rising from the wooden base of the instrument. The flywheel is supported in a similar manner by pivot socket g'. These sockets, which are of 5/16-inch round brass rod, soldered into turned brass foot pieces, h, are drilled longitudinally in the lathe with a 1/8-inch twist drill to a depth of 2 3/4 inches. To reduce friction as much as possible, the parts of the pivot rods within the sockets are filed down slightly in their middle so that they may bear against the sides of the sockets for short distances only, near the tops and bottoms of the holes.

Fig. 198 - Plan view of the motor.

A circular polished plate, i, of sheet brass, centrally located on the upper face of the wheel serves to give the latter a finish, and to assist in binding it with small screws upon the turned wooden hub, k. Into the ball, b', is inserted vertically a short pier. l, of 3/8-inch round wooden rod having a rounded top to reduce the friction between itself and the connecting rod whose end it supports. A round-topped conical wooden crank pin, m. rising from the wheel, supports the other end of c. The lower end of m is turned down slightly and glued into a 1/4-inch hole bored through one of the arms of d near the hub. The connecting rod, c, works freely on two slender wire nails which pass loosely through transverse holes in the rod near its ends and enter l and m respectively.

On the base of the machine on opposite sides of g, and at equal distances from it, are erected vertically, and parallel with each other, two rectangular pieces of double-strength window glass, n. each measuring 6 3/8 x 5 3/8 inches, the glasses being held firmly with shellac between the square wooden cleats, o. Upon the upper corners of each glass are cemented with shellac two solid wooden balls, p and p', the balls being slotted to a depth of 3/4 inch to receive the glass. The two balls on each glass are electrically connected with each other through a straight stiff wire passing between them, the exposed portion of the wire being covered for purposes of insulation with lengths of glass tubing, q.

Fig. 199 - The static electric motor.

In each of the balls, p', a little above its horizontal center, a small hole, r, is bored, somewhat slantingly downward, to receive the ends of the conducting cords or wires connecting the two pairs of stationary balls, respectively, to the positive and negative poles of the static machine. The exact distance apart of the holes in c, also the radius of the circle described by the movement of the crank pin, m, are not given on the drawing, as it is best to determine these experimentally. The latter should be such as will give about 3/16-inch clearance space between the stationary and the moving balls at the end of the latter's travel. To determine the former accurately, a temporary experimental rod of flat thin wood should first be made. By a few experiments with differently spaced pairs of trial holes in the wooden rod a distance will be found which will evenly divide the clearance room between the stationary and the moving balls at both extremes of the motion of the lever. When the proper distance is found the vulcanite rod may be marked and drilled from the wooden pattern.

The hollowing out of the moving balls, by reducing the weight, adds considerably to the speed of the motor, and is effected as follows: After being bored to a depth of 3/4 inch, and fitted to receive the lever, a, and the vertical pin, /, the balls are neatly split apart through the centers of the bored sockets by carefully driving into them a thin-bladed case knife, which will open them with very little bruising. With a small, sharp gouge each half is hollowed out until its walls are not more than 1/8 inch thick, removing all of the material that can be spared without cutting away the bored sockets. The halves are then glued together again, Before assembling the parts all of the balls must receive a conducting coating of tinfoil. This may be neatly done in the following manner: The ball is first given a sizing of shellac and allowed to dry thoroughly; it is then well smoothed down with and paper. Next prepare two round pieces of foil about 1 1/2 inch across, slitting each piece inward from its edge for a distance to about 1/3 its diameter. A place upon the ball equal in to that of the foil is now shellacked, as is also one side of the foil itself. Wait a few moments until the varnish has become c|uite "tacky," then lay the foil in position with the varnished side against the varnished place on the ball and press down into place, allowing the slitted flaps to overlap to prevent undue wrinkling. Proceed in like manner with the second piece, locating it as exactly as possible on the opposite diameter of the ball. The uncovered zone around the equator of the ball is now covered, a piece at a time, with strips of foil reaching across it from one end piece to the other, and as wide as can be applied without excessive wrinkling, varnishing only such portion of the ball at a time as will be covered by the strip to be applied. To avoid too much overlapping of each other at their ends the strips are made somewhat narrower at their ends than at their middle. After the ball is covered all loose corners or edges of foil should be carefully shaved off and any wrinkles or rough places nicely burnished down with a lead pencil or some smooth implement. An almost invisible point left projecting might seriously impair the working of the motor by allowing a silent escape of the electricity into the air. All the working joints must be made sufficiently loose to insure perfect freedom of movement without any possibility of cramping or binding, for it must be remembered that the mechanical forces of static electricity are of a very delicate nature. In operating, to get the best effects, some experimentation will be necessary to ascertain the proper degree of electrification; too vigorous excitation will be found as undesirable as too feeble. If the foregoing conditions have been complied with, the motor will run very satisfactorily from a small Holtz or Wimshurst machine. its speed being about 175 revolutions per minute. The completed machine is shown in perspective in Fig. 199. The action of the instrument depends upon the well-known physical principle of attraction between unlike and repulsion between like electrical states. When covered wires are run from the opposite poles of the generator to the two pairs of fixed balls, the latter become charged, respectively, with positive and negative electricities. The movable balls, being as yet uncharged, are attracted and drawn toward the nearest of the electrified stationary halls, until coming close enough, each moving ball receives a spark and becomes identical in polarity with the ball that has attracted it. Attraction is now instantly changed to repulsion, and the lever begins to reverse its movement. The moving balls, now bearing charges opposite in sign to those of the fixed balls they are approaching, are strongly attracted by the latter, while repelled by those they are receding from. This state persists until the moving balls, gaining fresh sparks of opposite sign to those they first received, have their electrification reversed and are again repelled. A continuous oscillation of the lever with rotation of the wheel results. With its crisp-clicking sparks, its general air of brisk activity, and the interesting play of the group of curiously correlated forces visibly demonstrated, the experiment is a most pleasing and attractive one.