One of the shanks may be provided with a discharge ball at the end as shown by _D B_ in Figure 44. The other is provided with a hard rubber handle made from a piece of rod. Bore a three-eighths hole directly in the top of each brass ball to receive the quadrant rods forming the spark-gap. [Illustration: Fig. 42.—A Comb or Collector.] The quadrant rods extend over the top of the plates and are three-eighths of an inch in diameter. They are loose in the tops of the balls so that they may be moved about or removed entirely. A small brass ball three-quarters of an inch in diameter should be soldered to the top of one of the quadrant rods and a similar ball two inches in diameter to the other. [Illustration: Fig. 43.—Showing how the Tinsel Brushes are arranged on the "Neutralizer" Rods.] Two large brass balls, two inches in diameter, are fitted over the ends of the axles, which project through the uprights. Bore a one-quarter-inch hole through each ball at right angles to the axle and slip a one-quarter-inch brass rod through and solder it fast. [Illustration: Fig. 44.—The Complete Wimshurst Electric Machine. B B B B, _Brushes_. C C, _Combs_. D B, _Discharge Ball_. I I, _Glass Rods_. H, _Handle_. Q Q, _Quadrant Rods_. S S S S S, _Sectors_. S G, _Spark-Gap_. P P, _Driving-Wheels_. For the sake of clearness, several of the sectors are not shown.] The ends of the rods should be tipped with a bunch of tinsel or fine copper wires and be curved so that the brushes so formed will just touch the sectors on the disks when the latter are revolved. These are the neutralizers and are arranged in the approximate positions shown in Figure 44. The driving-wheels are connected to the bosses by means of small round leather belts. The belt at the rear of the machine is crossed in order to make the plates revolve in opposite directions. If the machine has been properly built it is now ready for operation. It may be necessary to charge the machine the first time that it is used by touching several of the sectors with the charged cover of an electrophorus. Then if the handle is turned the accumulated electricity should discharge across the spark-gap at the top of the machine in the form of bright blue sparks. Experiments with an Electric Machine Many interesting experiments can be performed with an electric machine. The number is almost unlimited. A few of the most instructive ones are described below. Others can be found in almost any text book on physics. *The Leyden jar* consists of a glass jar coated with tinfoil part way up on both the outside and inside. Through the wooden stopper passes a brass rod or a heavy copper wire which connects with the inner coating of tinfoil by means of a small brass chain. The upper and outside end of the rod usually terminates in a brass ball or knob. It is a very simple matter to make a good Leyden jar. [Illustration: Fig. 45.—The Leyden Jar.]