Let us now try the machine and learn if it will work. In the first experiment we will remove the condensers temporarily, and setting the discharge balls within 1' of each other, we turn the crank of the machine from left to right. After about twenty turns of the crank the machine will run harder, which shows it is generating, and a stream of sparks will flow between the discharge balls. These may now be separated to about 11/4", and the sparks will still continue to flow. A separation of more than l1/2" will stop the sparks, and what is called the "brush" discharge begins. This consists of a stream of pale blue electricity bursting out from the right-hand discharge ball, and is accompanied by a strong smell of ozone. This discharge is quickly attracted by the approach of any conductor, such as the hand, and the sensation when the brush touches the latter is like the feeling of fine cobwebs.

As the machine is found to generate correctly, we will replace the two condensers and proceed to discharge them. See that the brass rods of the condensers touch the arms, W, leading to the discharging rods, and that the bases of the jars are in good contact with the tin-foil strip on the base. Now turn the machine again, having set the discharge balls about 8" apart. A much larger operation of the machine is necessary in this case; but very soon a decided resistance is felt, and a thick white spark will strike between the balls with a quite startling report, and this, will be repeated about every fifteen turns of the crank as long as the machine is in motion. On cold days I have been able to get as much as five inches of spark from my own machine.

I would say here that care should be taken not to approach the face or hands near the bare metal of the machine, as it is quite possible to get a very powerful and unpleasant shock from it when the condensers are attached. Use the wooden handle shown in Fig. 4 to regulate the length of the spark gap. There are hundreds of experiments which can be performed with this machine, but a description of them is not within the scope of this article, as they can be found in any elementary book on physics. I have appended a list of the prices of the various materials used in building this machine, and have set a maximum cost on each article, to be on the safe side. The list could, no doubt, be scaled down by most amateur workmen by the use of materials to be found in almost every household. I hope that the directions given in this article will enable the aspiring amateur to build the machine to his satisfaction, and that he will have as much pleasure from its use as I have had from mine.

List of Materials.

Wood for frames of glass drill and machine

$

.60

Three-quarter-inch copper tube for drilling glass

.10

Emery powder and turpentine ....

.10

Two 15" glass plates, cut to order

.50

Nine feet of No. 10 brass wire

.10

Sheet brass 10" x 4" No. 26 Stubbs gauge .

.10

One-quarter-inch smooth round-steel bar 10" long

.15

Two hard-rubber tubes 9 1/2|" long ....

.50

Nine 1/2" brass balls

.27

One 3/4" brass ball

,05

Ten sheets 6" x 8" tin foil.....

.75

Shellac varnish (white)

.10

Van Stan's cement......

.05

Two 4" screw pulleys

.30

Iron rod for axle for pulleys

.10

Six feet 1/4" round belt at 10c. ....

.60

Tinsel or sheet copper for brushes

.05

Two pint jars (white glass) for condensers .

.20

Corks for jars

.10

Screws, nails, copper, wire, etc.....

.25

$4.97