E. II. Williamson, Jr.

Almost the first piece of apparatus which the amateur in electrical experiments wishes to construct is a machine to generate statical electricity. It used to be called "frictional" electricity, and the term was no misnomer. I distinctly remember how my arm used to ache while grinding away at the first machine I constructed, with the amalgamated cushion screwed tightly against the old wine bottle which served as a cylinder. But such a primitive instrument soon ceased to satisfy my ambitions, and, after numerous experiments and failures, I at last succeeded in making a Wimshurst Influence machine which, although crude in appearance, worked well and seldom refused to generate even in the dampest weather. It was built with such tools as are usually to be found in the amateur workroom, and without using a turning lathe. This invaluable accessory to the workroom I did not then possess, and it can be dispensed with in -constructing this electrical machine, although it would simplify the making of some of the parts considerably.

The tools that are absolutely necessary are as follows: a cross-cut saw, compass saw, hack saw for cutting metal, breast drill to hold drills up to 1/4", 1/4" and 1/2" twist drills, square screwdriver, large rough file for wood, small flat file, small vise, a bit brace and one each 3/4", 1/2", 3/8" bits, wire pliers and pincers, shears for cutting thin sheet metal, soldering iron, solder and flux. The directions given here below are for a machine with plates 15" in diameter as, in my opinion, there is no economy in smaller sizes.

I will endeavor to give the reader full detail for each portion of the work, thus avoiding the difficulties which I had to overcome by experiments.

In the first place, hunt up an old cardboard box, such as the tailors use for sending home suits, selecting one with a heavy lid and bottom and at least 15" across. Take a pair of pencil dividers and lay out a circle 15" in diameter on each piece of card, marking the center plainly with a pencil or pen for future reference. Cut out the two circles, following the pencil lines carefully, and, armed with a tube of photo-paste, carry them to the nearest paint and glass store. Select two sheets of clear window glass, lay them on the counter and paste on the cardboard circles, one on each glass. The glass should be of such size as to leave an inch margin at least, around the card pattern. Now get the glazier to cut smoothly around the card with his diamond, and break away the surplus glass. This makes a better job than trying to do it yourself with a steel wheel glass cutter.

A Wimshurst Influence Machine 146

Fig. 1.

Having carried home the plates, we will prepare for the hardest part of the work, that is, cutting the holes in the center of the plates. The best method to accomplish this is that suggested by Mr. George Hopkins in his book "Experimental Science." (Fig. 1.) Set a piece of 3/4" board 18"/ square, also two pieces 4" wide and 6" high, B 13. These are nailed to the ends of A. Two pieces 4" wide, one 16" long, C, and one 18" long, D, are nailed across from B1 to B2, as shown in the figure. In the center of D, bore a perpendicular hole 3/4" diameter, straight down through D and C, but not into A. The board C should be fixed 2" above A. Buy a piece, F, of copper pipe 3/4" diameter and 1' long. File both ends square. Select a broomstick 3/4" thick and from this cut a piece, E, 7" long and cut away one end until it can be forced firmly and square into the end of the copper pipe for half an inch.

A Wimshurst Influence Machine 147

Fig. 2.

This is the drill for the glass, and the best method of revolving it is to put a dull bit in your breast drill and start boring a hole in the center of the upper end of the broomstick standard E. If a breast drill is not available, a bit stock will answer, but much care must be used. Detach one of your cardboard discs from the glass plate and with your compasses strike a 3/4" circle, using the old center. Lift the copper tube F, and slide the cardboard on to A, until the tube rests exactly on the small penciled circle, and fasten the card in that position. Now lay your glass circle upon the card so that the edges coincide exactly, and fasten the glass immovably with small screws at the edge. Get some fine emery powder (No. 80) and turpentine, and having wet glass and tube with the latter, scatter some emery on the glass under the drill, and commence turning the breast drill slowly. Do not press too hard, but let the drill cut slowly and steadily. Renew the turpentine and emery frequently, and, with care, the plate can be perforated in about twenty-five minutes, leaving a smooth round hole a little over 3/4" across. Just before the drill breaks through is the critical moment, and exceptional care must be used at this time.

Cut the second glass the same way, and when both are bored take a small file, and having wet it well with turpentine, cut a little niche on opposite sides of each hole, working very gently. The plates may be put aside now for the present, while we turn our attention to the frame of the machine.

The base, H (Fig. 2), is of 1" white pine, 8" wide and 20" long. The uprights, I1 \\ are of 1" pine, 10" high and 6" wide at the bottom, cut as shown, with sloping sides and a rounded top. The lower ends of these standards] are to be cut perfectly square and are screwed firmly to the base, H, in a central position as to-the length of the base, and 5" apart from between the inside faces, A 3/16" hole, J, is bored in each,. 81/2" from the bottom of each standard. When the latter are screwed in place, the holes should be exactly in line. At each end of the base, H, a 3/4" hole is bored in the center, 1" from the end.